TITLE PAGE
“MAGDALENA POTAMODROMOUS MIGRATIONS: EFFECTS OF REGULATED
AND NATURAL HYDROLOGICAL REGIMES”
by
Silvia López-Casas, MSc
Presented to the Faculty of the Graduate School
of the University of Antioquia
in partial fulfilment of the requirements
for the degree of
Doctor in Biology
in the Institute of Biology
Faculty of Natural Sciences
UNIVERSITY OF ANTIOQUIA
(Medellín)
December 2015
DEDICATION
To Anil
ACKNOWLEDGEMENTS
I want to thank Fernanda, Angelo, Miguel and Carlos for their unconditional help, support and
friendship, as well as for guide me with care and patience in each instance of this endeavour. I
am very grateful with Daniela Defex, Angela Jaramillo, Juan David Cano, Cintia Moreno, Isabel
Pareja and Mauricio Arias for their assistance and commitment with fish sampling and tagging.
I am also grateful with all my laboratory friends in Colombia, who supported me in times of
despair: thanks for preventing me from running away or from throwing off the balcony all the
otoliths. I also want to thanks Angela Gutierrez, Natalia Lacerda, Bia Almeida, Erick Santana,
Rosimeire Antonio, Karla Agostinho and Ana Clara Agostinho for their teachings, friendship,
companionship and love during my Brazilian days of learning and otolith cutting.
Of course, nothing would have been possible without my family and closest friends who help
me whenever I need, and unwittingly encouraged me to finish, so infinite thanks and deep love
to Mami, Papi, Juanchito, Anil and Lilo, Angélica, Pacho, el Cale and Yodys.
To ISAGEN S.A. for their interest and for funding the project. Especially to the Environmental
Management Department, headed by Claudia Alvarez, and to biologists Clara Perez, Veronica
Duque and the hydrologist team for their commitment to building knowledge for environmental
management of water resources in the country.
To Rainer Wedler who allows me the use of his fish illustrations.
To all La Miel fishermen who participated in the project and taught me new things about rivers
and fish, as well as all artisanal fishermen who reported a tagged fish.
To The World Academy of Sciences - TWAS for my Brazilian fellowship.
Special thanks to Alexandre Godinho, Konrad Gorski and Juan Jacobo Schmitter-Soto, whom
spent a lot of time reading, traveling and thinking to improve the final product of this research.
iv
ABSTRACT
The flood pulse is the most important force determining seasonality in neotropical rivers and
their fisheries. Fish migrations and spawning are highly dependent of water level.
Potamodromous fish sustain fisheries in the Magdalena River Basin. After the construction of
the Pantágoras dam in La Miel River, at Middle Magdalena Basin, flow regimen changed and
local fishermen complained about a catches decrease. To evaluate the effect of water level
fluctuations (hydropeaking) by dam operation on fishery catch and migration, and to determine
the impact of the Miel I hydropower plant on fish movements, mark-recapture experiments were
performed during six migratory periods in La Miel River Basin. The catch- per- unit- effort CPUE was recorded in different sampling sites during different flow scenarios given by the
water discharge of hydropower generation. Additionally, experimental monthly fishing was
performed in one of the main tributaries (Manso River) during three consecutive years.
Fishermen captured 32,727 individuals (56 fish species). The most important species were
migratory Characiformes: Prochilodus magdalenae, Leporinus muyscorum and Ichthyoelephas
longirostris. Both annual upstream migrations are about 30 to 45 days long; after that, with the
onset of the rainy season, fish spawn and remain in the river (resident individuals) or start a
downstream movement (the bajanza) to return to the Magdalena floodplains (nursery, shelter
and feeding grounds). At least P. magdalenae is able to perform consecutively both annual
upstream migrations. To explain the two upstream migrations a new hypothesis is proposed:
Magdalena upstream migrations are performed by the same population but just one fraction is
able to perform both, subienda and mitaca consecutively, due to the energetic costs of this
display, maintaining “migrant” and “non-migrant” individuals in a transitory state (fish will
eventually belong to any of these categories in accordance with their energy reserve). The
generation of hydroelectric power altered habitat features, affecting the effectiveness of fishing
gear, fish density and fish distribution. CPUE between migratory seasons showed a positive
trend with mean discharge during migration. Potamodromous fish interact with the discharge
tunnel and surge chamber of Miel I hydropower plant, but are able to find the exit and usually
start a downstream movement to find an alternative migration route. Additionally, differences
in rainy seasons by ENSO cycles caused differential flooding during the study period, affecting
the migration abundance and size of fish involved in reproductive migrations. These results
evidence that changes in flow and water chemistry due to hydropower generation could change
v
the migration patterns, affecting CPUE; that flow regulation during migration may change the
attractiveness of the river, affecting the total CPUE; that natural flow regimen of the Magdalena
River Basin affects fish length and weight gain and recruitment, affecting CPUE not just during
the migratory season but also in the following years; and that fish do not use the surge tank as
reproductive habitat. Changes in CPUE could affect human populations who depend of fishing
as an economic activity. This project was funded by ISAGEN SA (contract 46/3296).
Keywords: freshwater migratory fish, flow regime, hydropeaking, mark-recapture, migration
pattern, ENSO cycles.
vi
RESUMEN
El pulso de inundación es la fuerza más importante en determinar la estacional en los ríos
neotropicales y sus pesquerías. Las migraciones de peces y el desove son altamente dependientes
del nivel del agua. Las pesquerías en la cuenca del río Magdalena son sostenidas por peces
potádromos. Tras la construcción de la presa Pantágoras en el río La Miel, en el Magdalena
medio, el régimen hidrológico cambió y los pescadores se quejan de una reducción en las
capturas. Para evaluar el efecto de las fluctuaciones del nivel (hydropeaking) por la operación
de la central en la migración y las capturas, y para determinar el impacto de la central
hidroeléctrica Miel I en las capturas de los pescadores y los movimientos de los peces,
experimentos de marca y recaptura fueron realizados durante seis periodos migratorios en la
cuenca del río La Miel. La captura por unidad de esfuerzo-CPUE fue registrada en diferentes
puntos de muestreo durante diferentes niveles del río dados por la operación de la central
hidroeléctrica. Adicionalmente, mensualmente se realizó pesca experimental en uno de los
principales tributarios (río Manso) durante tres años consecutivos. Los pescadores capturaron
32.727 individuos (56 especies). Las especies más importantes fueron Characidos migratorios:
Prochilodus magdalenae, Leporinus muyscorum and Ichthyoelephas longirostris. Las dos
migraciones anuales duran entre 30 y 45 días, después de eso, con la llegada de las lluvias, los
peces desovan y permanecen en el río (individuos residentes) o inician un movimiento
descendente (la bajanza) para retornar al plano inundable del río Magdalena (hábitats de refugio
y alimentación). Al menos P. magdalenae es capaz de realizar consecutivamente dos
migraciones ascendentes anuales. Para explicar las dos migraciones ascendentes se propone una
nueva hipótesis: Magdalena migraciones ascendentes se llevan a cabo por la misma población,
pero sólo una fracción es capaz de realizar tanto, subienda y mitaca forma consecutiva, debido
a los costes energéticos de esta pantalla, el mantenimiento de "migrante" y "no migrantes"
individuos en un estado transitorio (pescado finalmente pertenecerán a ninguna de estas
categorías de acuerdo con su reserva de energía). Estos resultados evidencian que la generación
hidroeléctrica altera las características de hábitat, afectando la efectividad de las artes de pesca,
la densidad y distribución de los peces. La CPUE entre los periodos migratorios mostró una
tendencia positiva con la descarga media durante la migración. Los peces potádromos
interactúan con el túnel de fuga y la caverna de oscilación de la central Miel I, pero son capaces
de encontrar la salida y usualmente inician un movimiento descendente para encontrar una ruta
vii
alterna de migración. Adicionalmente, las diferencias en las estaciones lluviosas por los ciclos
ENSO causaron inundaciones diferenciales durante el periodo de estudio, afectando la
abundancia de las migraciones y el tamaño de los peces involucrados en las migraciones
reproductivas. Concluyo que los cambios en el flujo y la química del agua debidos a la
generación hidroeléctrica pueden cambiar los patrones migratorios, afectando la CPUE; que la
regulación del flujo durante la migración puede cambiar el atractivo del río, afectando la CPUE
total y que el régimen natural de flujo del río Magdalena afecta el incremento en peso y longitud
de los peces y su reclutamiento, afectando la CPUE no sólo durante la estación reproductiva
sino también durante los años siguientes; y que los peces no usan la caverna de oscilación como
hábitat reproductivo. Los cambios en la CPUE pueden afectar a las poblaciones humanas que
dependen de la pesca como actividad económica. Este proyecto fue financiado por ISAGEN
S.A. (contrato 46/3296).
Palabras clave: peces migratorios de agua dulce, régimen hidrológico, hydropeaking, marcarecaptura, patrón migratorio, ciclos ENSO.
viii
PREFACE
As part of the Magdalena River Basin, La Miel River and its main tributaries, the Manso and
Samaná rivers, share the fish species found in Magdalena Basin. As part of the system, is used
as reproductive habitat for potamodromous fish species that swim from the floodplain through
the main channels of the basin during the two annual periods of low water levels.
After the construction of the Pantágoras Dam and the beginning of power generation in the Miel
I hydropower plant in 2002, the hydrological regime in La Miel River changed. With the aim of
preventing or mitigating potential biological effects, in 2009, ISAGEN SA and the University
of Antioquia, through its Research Group of Ichthyology - GIUA, signed the interagency
agreement "Dynamics of the fish community in the Lower Basin of La Miel River, under
different hydraulic scenarios" (contract 46/3296) within which this research proposal is framed.
As part of this project and in partial fulfilment of the requirements for the degree of Doctor in
Biology, in the pages below I will present some results and new information to understand the
effects of the new hydrologic behaviour of La Miel River on potamodromous fish. I will explore
the effects on fish movements in the basin and the interaction with Miel I structures; the impact
of local flow regime and the effects of regional hydroclimatology patterns in fish migrations and
its fisheries.
ix
TABLE OF CONTENTS
TITLE PAGE .............................................................................................................................. i
DEDICATION ..........................................................................................................................iii
ACKNOWLEDGEMENTS ..................................................................................................... iv
ABSTRACT ............................................................................................................................... v
RESUMEN ...............................................................................................................................vii
PREFACE ................................................................................................................................. ix
TABLE OF CONTENTS .......................................................................................................... x
LIST OF TABLES ................................................................................................................... 12
LIST OF FIGURES ................................................................................................................. 14
LIST OF PHOTOGRAPHS ................................................................................................... 17
CHAPTER 1: INTRODUCTION .......................................................................................... 18
HYPOTHESIS ....................................................................................................................... 24
OBJETIVES .......................................................................................................................... 24
GENERAL......................................................................................................................... 24
SPECIFICS ........................................................................................................................ 24
STUDY AREA ...................................................................................................................... 25
CHAPTER 2: POTAMODROMOUS IN MAGDALENA RIVER BASIN: BIMODAL
MIGRATION PATTERN IN NEOTROPICAL RIVERS .................................................. 29
INTRODUCTION ................................................................................................................. 29
MATERIALS AND METHODS .......................................................................................... 31
Fish tagging ....................................................................................................................... 31
Data analysis ...................................................................................................................... 33
RESULTS .............................................................................................................................. 33
DISCUSSION ....................................................................................................................... 43
CHAPTER 3: POTAMODROMOUS FISH IN A SURGE CHAMBER: THE CASE OF
MIEL I HYDROPOWER PLANT ........................................................................................ 50
INTRODUCTION ................................................................................................................. 50
MATERIALS AND METHODS .......................................................................................... 52
Data collection and sampling ............................................................................................ 52
Fish tagging ....................................................................................................................... 53
Ichthyoplankton ................................................................................................................. 55
Data analysis ...................................................................................................................... 55
RESULTS .............................................................................................................................. 55
x
Fish species into the surge chamber .................................................................................. 55
Fish movements ................................................................................................................. 56
DISCUSSION ........................................................................................................................ 61
Fish species into the surge chamber .................................................................................. 61
Fish movements ................................................................................................................. 63
CHAPTER 4: FISHING IN A REGULATED RIVER: HYDROPEAKING EFFECTS
ON CATCH PER UNIT EFFORT......................................................................................... 66
INTRODUCTION ................................................................................................................. 66
MATERIALS AND METHODS .......................................................................................... 68
Data collection and Analysis ............................................................................................. 68
RESULTS .............................................................................................................................. 71
DISCUSSION ........................................................................................................................ 79
CHAPTER 5: ENSO CYCLES EFFECTS IN INLAND FISHERIES AND
POTAMODROMOUS MIGRATIONS IN TROPICAL SOUTH AMERICA.................. 86
INTRODUCTION ................................................................................................................. 86
METHODS ............................................................................................................................ 88
Data collection and analysis .............................................................................................. 88
RESULTS .............................................................................................................................. 90
DISCUSSION ...................................................................................................................... 106
CHAPTER 6: GENERAL CONSIDERATIONS AND IMPLICATIONS FOR
FISHERIES MANAGEMENT ............................................................................................. 113
REFERENCES ...................................................................................................................... 118
ELECTRONIC REFERENCES .......................................................................................... 130
xi
LIST OF TABLES
Table 1. Numerical and biomass abundances during four migratory seasons (August 2010,
February 2011, August 2011 and February 2012), for potamodromous species captured in La
Miel River Basin, number of tagged individuals and recovered data of each species. ............. 34
Table 2. Number of individuals recaptured in each tagging place, distance between release and
recapture sites and time (minimum and maximum) between release and recapture. Zero time
and distance correspond to the time and place of release. * Sites within La Miel River Basin.
................................................................................................................................................... 39
Table 3. Minimum, maximum and mean distance (in km) and estimation of swimming speed
(km/day) of migratory species tagged in La Miel River Basin. ................................................ 43
Table 4. Number of fish caught by species in the surge chamber (CO), discharge tunnel (TF),
and captured in the discharge tunnel and released into surge chamber (TF / CO) for sampling
species. + Migratory species. ..................................................................................................... 56
Table 5. Places of fish tagging and recapture. TF: Discharge tunnel; CO: Surge chamber;
LMRB: La Miel River Basin; MR: Magdalena River; CCC: Floodplain lakes or connection
channels. .................................................................................................................................... 58
Table 6. Distance travelled (km) and time (in days) elapsed between release and recapture of
individuals of migratory species tagged and released in Miel I discharge tunnel and surge
chamber. Time and distance zero corresponds to the moment of release. Negative distances
correspond to downward movements and positive distances to upward movements from their
releasing point. TF = Discharge tunnel, CO = Surge chamber, TF / CO = captured in discharge
tunnel and released in surge chamber, LMRB = La Miel River Basin, MR = Magdalena River;
CCC = Floodplain lakes or connection channels....................................................................... 59
Table 7. Categories for describing submerged and exposed habitat. Scores denote structural
complexity of each of the substrates, where one is the structurally least complex and 10 the most
complex. .................................................................................................................................... 69
Table 8. Mean values, standard errors and 95% confidence intervals of the biomass and catch
per unit effort of fishing sessions at La Miel River Basin, and total number of replicas per
number of turbines and migration period. ................................................................................. 73
Table 9. Eigenvectors, eigenvalues, Broken-stick eigenvectors and percentage explanation of
the axes of axes 1 and 2 of the principal component analysis (PCA) applied to La Miel River
Basin habitat characteristics data matrix. .................................................................................. 74
12
Table 10. Crossed correlations of daily catch per unit effort (dCPUE) between pair of
consecutive sampling days for all the assessed migratory periods. Note that sampling in 2010,
2011 and 2012 were of 15 consecutive days, while 2008 were of 25 consecutive days. .......... 75
Table 11. Abundances and taxonomical classification of the species caught during the six
assessed migratory seasons in the low La Miel River Basin. Species in bold are recognized for
their migratory habits................................................................................................................. 93
Table 12. Proportion of immature (I) and mature (M) individuals for the four most important
potamodromous species during six upstream migrations in La Miel River Basin. ................... 98
Table 13. Percentage of the monthly numerical catches in the Manso River. Bold numbers were
used to calculate the total catch for each migration; highlighted months correspond to subienda
(first semester of the calendar year) and mitaca (second semester of the calendar year). ...... 102
Table 14. Magdalena River hydrological variables, potamodromous fish size variables and
CPUE for each semester: Mean Magdalena River water level and its standard deviation,
minimum and maximum water levels (Mean water level ± SD), number of days under the
minimum level (DUM = number of days<107.36), and over the maximum level (DOM = number
days>108.76). Mean multiannual water level (2002-2012). W = mean total weight (g); L = mean
standard length (mm); K = Fulton’s condition factor (K=W/L3, where W = the weight of the
fish, and L is the standard length in centimetres); and the total CPUE (individuals/throw) of each
assessed reproductive period. .................................................................................................. 105
13
LIST OF FIGURES
Figure 1. Daily flow of La Miel River: 1965 and 1999 prior to the start of the operation of Miel
I hydropower plant, 2004 current scenario (tunnel discharge). Source: IDEAM (1999) and
ISAGEN S.A. ............................................................................................................................ 21
Figure 2. Location of the study area and the six sampling sites on La Miel River Basin (TF=
discharge channel; Pal= La Miel River at Palmera; Man= Manso River; Cac= La Miel River at
La Cachasa; Sam= Samaná River and SM= La Miel River at San Miguel). The Magdalena River
flows from South to North. ........................................................................................................ 26
Figure 3. Miel I underground hydroelectric power plant. Note that the Surge chamber is located
between the powerhouse (machines chamber), and the exit of the water to La Miel River,
through the leakage or discharge tunnel. Modified from ISAGEN S.A (2015). ....................... 28
Figure 4. Potamodromous species captured and tagged in La Miel River during four migratory
seasons (August 2010, February 2011, August 2011 and February 2012). ............................... 35
Brycon rubricauda
Colossoma macropomum
Figure 5. Catches proportions of potamodromous
migrations of
Bryconspecies
rubricauda during the upstream
Brycon rubricauda
Curimata mivartii
Colossoma macropomum
Brycon rubricauda
Colossoma
macropomum
Magdalena
River
Basin
in
La
Miel
River.
P.
magdalenae
is
excluded
but
note
that
the
missing
Brycon
rubricauda
Cynopotamus
magdalenae
Curimata
mivartii
Brycon
rubricauda
Colossoma macropomum
Curimata mivartii
Brycon rubricauda
Colossoma
macropomum
Brycon
rubricauda
Ichthyoelephas
longirostris
Cynopotamus
magdalenae
proportion
100%
corresponds
to this species.
, Curimata
mivartii;
,Colossoma
Ichthyoelephas
macropomum
Curimata for
mivartii
Cynopotamus
magdalenae
Colossoma
macropomum
Curimata
mivartii
Colossoma
macropomumLeporinus muyscorum
Ichthyoelephas
longirostris
Curimata
mivartii
Cynopotamus magdalenae
Ichthyoelephas
longirostris
Curimata
mivartiimuyscorum;
Curimata
mivartii
longirostris;
,
Leporinus
,
Pimelodus
blochii;
,
Pimelodus
grosskopfii;
Cynopotamus
magdalenae
Pimelodus
blochii
Leporinus
muyscorum
Cynopotamus magdalenae
Ichthyoelephas longirostris
Leporinus muyscorum
Cynopotamus magdalenae
Cynopotamus
magdalenae
Ichthyoelephas
longirostris
Pimelodus Ichthyoelephas
grosskopfii
blochii
longirostris
muyscorum
,Leporinus
Pseudoplatystoma
magdaleniatum;
,Pimelodus
Salminus
affinis;
,
Sorubim
cuspicaudus.
Pimelodus
blochii
Ichthyoelephas
longirostris
Ichthyoelephas
longirostris
Leporinus
muyscorum
Pseudopimelodus
bufonius
PimelodusLeporinus
grosskopfii
Leporinus
Pimelodus blochii Leporinus muyscorum
muyscorum
Pimelodus grosskopfiimuyscorum
Pimelodus
blochii
Pseudoplatystoma
magdaleniatum
...................................................................................................................................................
Pseudopimelodus
bufonius
Pimelodus
blochii
Pimelodus
blochii 37
Pimelodus grosskopfii
Pseudopimelodus
bufonius
Pimelodus blochii
Pseudopimelodus bufonius
Pimelodus grosskopfii
Pseudoplatystoma Pseudopimelodus
magdaleniatum bufonius
Salminus affinis
Pseudoplatystoma magdaleniatum
Sorubim cuspicaudus
Salminus affinis
Other non-migratory
speciescuspicaudus
Sorubim
Pimelodus
grosskopfii
Salminus affinis
Pseudoplatystoma
magdaleniatum
Pimelodus
grosskopfii
Pimelodus
grosskopfii
Pseudoplatystoma
magdaleniatum
Pseudopimelodus
Sorubim cuspicaudus
Salminus Pseudopimelodus
affinis bufonius bufonius
Pseudopimelodus bufonius
Salminus
affinis
Pseudoplatystoma
magdaleniatum
Pseudoplatystoma
magdaleniatum
Other non-migratory
species magdaleniatum
Sorubim cuspicaudus
Pseudoplatystoma
Sorubim cuspicaudus
Salminus affinis
Salminus
affinis
Other non-migratory
species
Salminus
affinis
Other
non-migratory
species
Sorubim cuspicaudus
Sorubim cuspicaudus
Sorubim cuspicaudus
Other non-migratory species
Other non-migratory
species
Other non-migratory species
Figure 6. Fish recovery locations, each dot corresponds to one individual. ............................. 38
Figure 7. DistanceOther
travelled
andspecies
elapsed time between release and recapture of P. magdalenae
non-migratory
tagged and released in La Miel River Basin. Time and distance zero correspond to the moment
and place of release. Positive and negative values for distance correspond to upstream and
downstream movements from the tagging place. Note that dots correspond to movements within
La Miel River Basin (group 1), and triangles to movements out of the La Miel River Basin
(group 2). Also, note that the entrance to tributaries occurred during the first 31 days (white
triangles) or after the reproductive period in the lowlands (positive grey triangles). The return
(downstream migration) to Magdalena floodplain occurred after 45 days (negative grey
triangles) as well as the entrance to tributaries in the floodplain (positive grey triangles). The
fish populations have a proportion of individuals that do not undergo migration (black dots),
named as resident individuals, and a proportion that actively migrates, performing two
migrations by year: in February and August (grey dots near the 200 days). ............................. 41
Figure 8. Swimming velocity and size of recaptured individuals of migratory fish species tagged
and released in La Miel River Basin. ........................................................................................ 42
14
Figure 9. Diagrammatic representation of migratory cycles of Magdalena potamodromous fish.
................................................................................................................................................... 45
Figure 10. Recovery locations of fish tagged and released in the discharge tunnel and the surge
chamber of Miel I hydropower plant. Each dot corresponds to one individual. ....................... 57
Figure 11. Distance and time between release and recapture of migratory species individuals
tagged and released in discharge tunnel and surge chamber. Note that + corresponds to the
individual No. 999 captured in Iron Bridge; and * correspond to individuals that after making a
downward movement in the La Miel river basin, and in Magdalena River, performed a posterior
lateral movement, entering through a connection creek to a floodplain-lake. .......................... 60
Figure 12. Daily catch in La Miel River Basin in total dCPUE (daily kg/ daily throws) during
subienda (February) and mitaca (August). ................................................................................ 72
Figure 13. Average values of the first axis of Principal component analysis (PCA1) of sampling
stations in La Miel River Basin during one, two or three turbines flow discharge scenarios. The
vertical bars denote 0.95 confidence intervals. ANOVA: F(10, 667) =21.971; p=0.00. ............... 76
Figure 14. Scatterplot of mean daily discharge from Miel I hydropower generation (turbines
flow) and the total CPUE in La Miel River Basin during six migratory seasons (February and
August of 2008, August 2010, February and August 2011, and February 2012). Log 10 CPUE
= -2.0523 + 0.597·Log 10 Discharge (r2 = 0.63; p = 0.0601). .................................................. 77
Figure 15. Scatterplot of iCPUE and habitat features (first axis of the principal components
analysis: PCA1) during each fishing session during subiendas and mitacas in La Miel River
Basin. ......................................................................................................................................... 78
Figure 16. Mean catch per unit effort (iCPUE) by number of turbines during the fishing activity
in the six sampling stations of La Miel River Basin (see Figure 1: TF, Discharge tunnel; Pal, La
Miel River at Palmera; Man, Manso River; Cac, La Miel River at La Cachasa; Sam, Samaná
River and SM, La Miel River at San Miguel). Vertical bars denote +/- standard errors........... 78
Figure 17. Catch per unit effort (iCPUE) during subiendas and mitacas in La Miel River Basin,
by number of turbines during the fishing. Vertical bars denote 0.95 confidence intervals. Some
means are not estimable. ............................................................................................................ 79
Figure 18. Catch per unit effort for each of the assessed migrations in the lower basin of La
Miel River. ................................................................................................................................. 91
Figure 19. Daily landing proportion of P. magdalenae and all the others species during the six
assessed migratory seasons in the lower basin of La Miel River. February upstream migrations
are called locally subiendas while august migrations are called mitacas.................................. 96
Figure 20. Daily landing proportion of the commercial species during the six assessed migratory
seasons in the lower basin of La Miel River. ............................................................................ 97
15
Figure 21. Catch per unit effort in La Miel River Basin for migratory species and middle
Magdalena River water level (at Middle Magdalena Basin: Puerto Berrío Municipality). Note
that upstream migrations of 2008, 2010-mitaca, 2011 and 2012 subienda correspond to
migratory season assessed daily in the six sampling station of La Miel River Basin, while 2009
subienda and mitaca and 2010 subienda corresponds to monthly sampling of Manso station
during the months of the migratory event. ................................................................................ 99
Figure 22. Precipitation in percentages with respect to multi-year average between January and
December 2010. Well below normal: 0-30%, moderately below normal: 31-60%, slightly below
normal: 61-90 %, normal 91-110%, slightly above normal: 111-140%, rains moderately above
normal: 141-170% well above normal: greater than 170%). Taken from León (2010). ......... 100
Figure 23. Differences in standard length and total weight of potamodromous species in La
Miel River Basin during nine upstream migrations. Note that 2008 subienda and mitaca, 2010
mitaca, 2011 subienda and mitaca, and 2012 subienda correspond to migratory season assessed
daily in the six sampling station of La Miel River Basin, while 2009 subienda and mitaca and
2010 subienda corresponds to monthly sampling of Manso station during the months of the
migratory event (Table 12). ..................................................................................................... 103
Figure 24. Relations between catch-per-unit-effort, mean total weight and mean standard length
of Magdalena potamodromous fish and the standard deviation of Magdalena water level with a
time lag of one year. Thus, 2008-subienda was plotted with SD value of 2007-subienda and so
on. ............................................................................................................................................ 104
Figure 25. Magdalena River water level and and its standard deviation. ............................... 104
Figure 26. Schematic summation of environmental and biological conditions that affects the
size (length and weight) of individuals and the abundance of potamodromous fish performing
each migration in the Magdalena Basin. ................................................................................. 108
16
LIST OF PHOTOGRAPHS
Photography 1. Discharge tunnel view during high and low flows. ........................................ 27
Photography 2. Tagging methodology of potamodromous fish species in La Miel River Basin.
................................................................................................................................................... 32
Photography 3. Potamodromous fish accumulations in the discharge tunnel, and in the surge
chamber of Miel I hydropower plant during the second reproductive migration, mitaca, of 2010.
................................................................................................................................................... 51
Photography 4. Miel I surge chamber under experimental energy generation. ....................... 53
Photography 5. Fishing and fish releasing in the discharge tunnel and surge tank of Miel I
hydropower plant. ...................................................................................................................... 54
Photography 6. La Miel River at Cachasa during high water level (three turbines scenario) and
low water level (one turbine scenario). ..................................................................................... 84
Photography 7. Prochilodus magdalenae mouth (flannel mouth characiform) and mouth-prints
in submersed and exposed pebble-beach. .................................................................................. 84
17
CHAPTER 1: INTRODUCTION
A migration refers to movements resulting in an alternation between two or more separated
habitats (i.e. a movement away from one habitat followed eventually by a return again),
occurring with regular periodicity, and involving a large fraction of the population (Northcote,
1978).
Animal migration should be considered as a strategy for dealing with areas subject to sharp
fluctuations and frequent periods of inadequate conditions, in this way may be simply a more
formalized or exaggerated pattern of behaviour to optimize utilization of basic resources during
feeding or reproductive phases of their life history (Northcote 1978). From an evolutionary
perspective, migration involves specialized behaviours that have arisen through natural selection
(Dingle, 1980). Therefore, individuals behave so as to maximize their reproductive success or,
rather, their inclusive fitness (Krebs and Davies, 1993).
In general, migration is a strategy for optimize resources. Three main strategies can be
considered: optimizing the abundance, size and fertility in a population (food migrations);
minimizing the losses from the occurrence of unfavourable conditions appearance of
unfavourable conditions (migration evasion unfavourable conditions); and to ensure the success
of reproduction accompanied by optimal survival of eggs and larvae (McKeown, 1984).
Migration can simultaneously provide conditions for more than one of these aspects i.e. food,
evasion and/or reproductive migrations (Lucas & Baras 2001).
The best reproductive habitat rarely coincides with the best feeding habitat, particularly for
fishes occupying environments subject to marked seasonal or spatial changes in productivity. In
a sense, the reproductive habitat must be considered the “original” one, and migration as a
strategy to “scape” from its food restrictions, often thereby increasing growth, fecundity,
survival and thus natural production (Northcote, 1978).
Although tropical freshwaters do not have the marked summer and winter seasonality
characteristic of temperate and artic regions, the alternation between dry and wet season produce
effects on fish, which may in some way be similar (Lowe-McConnell, 1987). Conditions during
18
the dry season may induce migrations of young and adults, which in some respects are the
counter parts of wintering migrations of temperate and artic regions. When backwaters, marshes
and tributaries which form rich feeding habitats dry up, fishes are alike forced to move back into
the mainstem river channels, where food resources are probably much more limited (Roberts,
1972).
Most spawning migrations of tropical freshwater fishes are potamodromous movements within
rivers and their floodplains or from lakes to rivers. These seem to be timed so that adults and
young may exploit the rich resources that result from flooding (Northcote, 1978). In these cases,
feeding optimization is a prime strategy to increase abundance via changes in growth, fecundity
or survival. Therefore, it would explain why the important commercial species are migratory:
they are of commercial interest because they are abundant and abundant because they are
migratory (Northcote, 1978). This is also true for fish communities of major river systems in
South America, which contain a high proportion of detritivorous fishes in the families
Prochilodontidae and Curimatidae. These families include important migratory fish stocks that
in some regions comprise over 50 percent of the community ichthyomass (Bowen, 1983).
Consequently, one of the most recognized patterns in potamodromous migrations that take place
in South American rivers is the migration of species of the genus Prochilodus between spawning
and feeding areas (Godoy, 1972; Bayley, 1973; Lucas & Baras, 2001; Carosfeld et al., 2003;
Barletta et al., 2010).
As an adaptation to the aquatic habitat, around the world fish have evolved physiological
adaptations, life history strategies and spawning and feeding behaviour to cope with hydrology
and seasonality of fluctuating flow conditions in rivers (LoweMcConnell, 1987; Junk et al.,
1989; Bunn & Arthington, 2002). Fish have evolved physiological adaptations, life history
strategies and spawning and feeding behaviour to cope with hydrology and seasonality of
fluctuating flow conditions in rivers (LoweMcConnell, 1987; Junk et al., 1989; Bunn &
Arthington, 2002). Through these adaptations, different species are able to respond to changes
in flow in different ways. As a result, the relative abundance of species forming riverine fish
assemblages changes in response to natural variations in flood regimes between years
(LoweMcConnell, 2003).
19
The biology and ecology of fish in large rivers are strongly linked to the annual hydrological
regime in the main channel and the regular flooding of the associated floodplains (Welcomme
1985; Junk et al., 1989). Current pressures on water from other users, notably agriculture and
energy production, means that there is an increasing trend to control hydrological regimes. Such
interventions almost inevitably act to the detriment of living aquatic resources and fisheries
(LoweMcConell, 2003).
The power demand of a city, region or country has a variation throughout the day. The
generation of electrical energy must follow the demand curve, increasing power demand should
increase the power supplied (XM 2010). Temporary changes in supply and demand of energy
of the countries, coupled with changes in the daily schedules of energy production and its
replanning, regulate the flow of dammed rivers. Therefore, changes in water level that naturally
occur between months or seasons due to rain patterns, may occur in one day or in few hours,
generating a pulsing flow pattern known as hydropeaking. This alteration of flow regimes has
been recognized as the most serious and continuous ecological threat to the sustainability of
rivers, their floodplains and associated biota (Ward et al. 1989, 1999). One of the main reasons
for this is that has been documented states that flow is one of the major determinants of physical
habitat in rivers, which in turn is crucial in the distribution, abundance and diversity of
organisms in these systems, at all spatial and temporal scales (Vannote et al., 1980; Junk et al.,
1989; Poff & Ward, 1990; Bunn & Arthington, 2002; Wantzen & Junk, 2003).
The impacts of changing hydrological regimes on fish populations include habitat modifications
and variations in species diversity (Bunn & Arthington 2002), but dragging of early stages of
fish- lacking swimming abilities - (Lucas & Baras 2001), changes in habitat availability (Vocht
& Baras, 2005), and changes in thermal regimes and oxygen (hypoxia or supersaturation), have
also been documented. All these differently affecting each life stage of the fish.
Changes in fish populations and fish assemblages have been well documented as effects of dams
(Bunn & Arthington 2002). Among the most relevant, can be highlighted the decrease in
diversity, abundance, number of species, number of families and biomass through the years
(Agostinho et al., 2007; Sáenz & Solano, 2006); the migration reduction or elimination upstream
of the reservoir (Holden & Stalnaker, 1975; Lucas & Baras, 2001; Valderrama et al., 2006;
Ward & Stanford, 1989); the changes in communities upstream and downstream of the dam
20
(Agostinho et al., 2007; Greathouse et al., 2006; Ponton et al., 2000); and modification of
ecosystem services upstream and downstream of the reservoir (Hoeinghaus et al., 2009).
However, the environmental and ecological variations resulting from changes in the
hydrological profile of a river are complex, varied and multiple. The impact of each project is
unique and dependent not only on the structure and generation regime, of local sediment loads,
geomorphological constraints, and climate and key attributes of the local biota (McCartney et
al. 2000). In addition, little is known about the ecological consequences of reservoirs in tropical
river systems compared to temperate dams (Pringle et al., 2000; WCD, 2000; Greathouse et al.,
2006). While large-scale studies have quantified the effects of dams and flow fluctuations in
temperate systems in tropical regions similar assessments are rare or non-existent.
In La Miel River, after the beginning of the operation of the Miel I hydropower plant in the year
2002, the flow regimen of La Miel River changed. Before the operation of the dam, the river
had two periods with high waters and two with low waters, as is common for rivers of the
Magdalena basin, but after the dam, that pattern disappeared due to hydropeaking (Figure 1).
500
Before dam operation (1965)
Before dam operation (1999)
After dam operation (2004)
3
Daily river discharge (m /s)
400
300
200
100
0
Jan
Feb
Mar
Apr
May Jun
Jul
Aug Sep
Oct
Nov Dec
Month
Figure 1. Daily flow of La Miel River: 1965 and 1999 prior to the start of the operation of Miel
I hydropower plant, 2004 current scenario (tunnel discharge). Source: IDEAM (1999) and
ISAGEN S.A.
21
Thus, it is known that dams and operating system can have multiple effects on migration,
reproductive events and recruitment of migratory species of tropical fish, and that the effect of
each dam is unique and dependent on the life histories of the species that inhabit it. Previous
studies in La Miel River Basin showed that changes in flow due to power generation affect water
quality and habitat availability. Additionally, it was observed that migratory individuals of
Prochilodus magdalenae and Ichthyoelephas longirostris displayed a preference for the nonregulated tributary: the Manso River (Jiménez-Segura et al., 2008). But, (i) Does the changing
in water level by hydropeaking affect water quality and habitat availability for potamodromous
fish in La Miel River Basin? And (ii) Do these changes affect migration of potamodromous
species? That is to say, (iii) How does fish move during the reproductive migration in La Miel
River Basin under different flow scenarios given by the Miel I hydropower generation?; (iv) Do
they enter into non-regulated tributaries as an alternative route after finding the dam?; (v) Are
the preferences of non-regulated tributaries like the Manso River the result of the search for
better environmental conditions than those offered by La Miel River?; (vi) Which individuals
are entering into the surge chamber of Miel I hydropower plant?; (vii) Are those individuals able
to swim out of the surge chamber?, and (viii) how long do they stay there?.
The University of Antioquia in agreement with ISAGEN S.A. (a Colombian Hydropower
producer) signed the project “Dynamics of the fish community in the Lower Basin of La Miel
River under different hydraulic scenarios”. As part of this research, the fundamental questions
above raised the realization of my doctoral thesis, whose results I will present here.
The first chapter corresponds to an introductory part, in which the readers will find the
hypothesis, objectives and project justification, which was initially raised to answer the research
questions above. As well as the description of the study area.
In the second chapter, based on the results of a mark-recapture experiment, I described the
potamodromous migrations in terms of participating species, an approximation of the fish
movements, origin and fate of individuals who undertake such movements, swimming velocities
and the bimodal migratory pattern for the basin, which until now were based on little empirical
evidence or landing information.
22
In the third chapter, as part of the mark-recapture experiment, I described and discussed some
aspects of the entrance of fish into the surge chamber of the hydropower plant (through the discharge
channel) from La Miel River. I was able to determine the composition of the fish and evaluate the
potential effects on migration, the time that fish spend into the structure and the movements of fish
once they return to La Miel River.
The fourth chapter discusses the effects on fish movements and fisheries of water level changes
in La Miel River due to the Miel I hydropower plant generation. Through fishing in different
sampling sites in La Miel River during the reproductive season, and recording of the catch-perunit-effort – CPUE, I answered some of the fundamental questions of this research.
In the fifth chapter, through landing data analysis, inter-annual fluctuations in catch are
associated to El Niño–Southern Oscillation (ENSO), and some of its effects in Magdalena river
hydroclimatology and in inland fisheries and potamodromous migrations are discussed.
Finally, the sixth chapter compiles the main findings and the implications of this new knowledge
in the management of potamodromous fish populations and regulated rivers.
23
HYPOTHESIS
If potamodromous migrations in neotropical rivers are driven by flood pulse and its associated
changes in habitat, then changes in flow regime due to river damming or the occurrence of El
Niño–Southern Oscillation (ENSO) may have effects on the migratory patterns of the species,
and such changes have a negative impact on fish migrations and its associated fisheries.
OBJETIVES
GENERAL
Define the effect of changes in the hydrological regime of La Miel River, due to the operation
of the Miel I hydropower plant, and to regional hydroclimatology, on potamodromous
migrations and its associated fisheries.
SPECIFICS
Infer the migratory routes of potamodromous species within La Miel River Basin, including
some of the structures of Miel I hydropower plant non-regulated tributaries of La Miel River.
Determine if migrant individuals of potamodromous species entering through discharge tunnel
to the surge chamber of Miel I hydropower plant are permanent inhabitants of that place, and if
they are able to get out of this structure.
Describe the impact of changes in flow caused by the operation of Miel I hydropower plant in
the use and occupation of La Miel River Basin by individuals of potamodromous species that
come from the Magdalena River.
Describe the effects of inter-annual fluctuations in water levels due to El Niño–Southern
Oscillation (ENSO) in potamodromous migrations and it fisheries.
24
STUDY AREA
The Magdalena River Basin is the largest in Colombia and the major axis of economic
development in the country. Its basin is intensely populated with nearly 80% of the Colombian
population inhabiting it (Galvis and Mojica, 2007). Additionally, its basin represents 24%
(257,438 km2) of the country’s area (Jiménez-Segura et al., 2010). Due to the Andean geography
and its water production, the Magdalena River Basin has been the focus of many hydroelectric
development, comprising 84% percent of the Colombian reservoirs, most of them with dams
exceeding 15 m height, of which 32% are located between 0-1000 m.a.s.l. (Jiménez-Segura et
al., 2011).
The Magdalena River is located in the north-western region of South American continent, and
has a bimodal hydrological cycle with two rainy and two dry seasons in a single year. The basin
comprises two main drainage areas, the Magdalena and Cauca Rivers. Located on the eastern
slope of the western Andean Cordillera, La Miel River is one of the most important tributaries
of the Magdalena River (Figure 2). It has an average discharge of 359 m3s-1 (2006–2011), which
corresponds to 9.5% of the annual medium discharge of the Magdalena in its middle stretch. La
Miel River originates at 3600 m.a.s.l., it has an approximate length of 110 km, and it is
fragmented by the Pantágoras Dam, which is located 68 km downstream of the headwaters, at
274.5 m.a.s.l.
From the dam, the river flows for 46.7 km until it meets the Magdalena River, at 146 m.a.s.l.
(Figure 1). Downstream of the dam, there are two important tributaries: the Manso (19.6 ± 16.5
m3 s-1) and the Samaná (165.6 ± 130.9 m3 s-1) rivers. To cover the area, six sampling stations
were located in the basin: four in La Miel River including the discharge tunnel (TF) of the Miel
I hydroelectric power plant and its two main tributaries (Figure 2). The nearest floodplain lakes
are 42 km downstream from the mouth of La Miel River.
Fishing activities in La Miel River are independent of the hydrological period, with fishermen
fishing from five to seven days per week during either the high or low water periods. La Miel
River Basin has three major fishing ports: La Habana (13 km downstream of the discharge
channel and 2.6 km upstream of Manso River mouth), San Miguel (SM, downstream of Samaná
River mouth), and Buenavista (near La Miel River mouth in the Magdalena River). The total
25
catch is estimated in 52 t fish/year, being February to March and July to October the months of
peak production (Reínoso-Florez et al., 2010).
Figure 2. Location of the study area and the six sampling sites on La Miel River Basin (TF=
discharge channel; Pal= La Miel River at Palmera; Man= Manso River; Cac= La Miel River at
La Cachasa; Sam= Samaná River and SM= La Miel River at San Miguel). The Magdalena River
flows from South to North.
The Pantágoras Dam is part of the Miel I Hydroelectric plant; it was built over La Miel River
and with a height of 188 metres (the second highest in the world) and length of 340 metres at
the crest, it stems all the water discharge of La Miel River. The hydroelectric plant is
underground and located on the left bank of La Miel River. It returns the water to the river
through the discharge tunnel (TF), 4.5 km downstream of the dam (Photography 1), and thus
leaves a stretch of 4.5 km of riverbed almost dry (called locally Puente Hierro). Flow in this
stretch of the river is caused by local rains and small creeks that discharge from small tributaries.
26
Photography 1. Discharge tunnel view during high and low flows.
The discharge tunnel is 4.1 km long, and 9.1 m diameter that has at the exit a reinforced concrete
structure with two platforms, one on each side. The plant has an installed capacity of 396 MW
(megawatts) in three Francis turbines, with a power rating of 132 WM at 300 rpm. The total
discharge capacity is 250 m3 /s (approximately 74 m3/s for each turbine). The Miel I
hydroelectric power plant has a surge chamber fitted between the powerhouse and the discharge
tunnel to absorb pressure transients caused by the normal operation of the machines due to
sudden changes in pressure and flow. From there, through a restriction orifice located at the
bottom of the chamber as a siphon, the water returns to the river through the discharge tunnel
(Figure 3).
27
Figure 3. Miel I underground hydroelectric power plant. Note that the Surge chamber is located
between the powerhouse (machines chamber), and the exit of the water to La Miel River,
through the leakage or discharge tunnel. Modified from ISAGEN S.A (2015).
28
Magdalena potamodromous migrations
CHAPTER 2: POTAMODROMOUS IN MAGDALENA RIVER BASIN: BIMODAL
MIGRATION PATTERN IN NEOTROPICAL RIVERS1
Abstract: Magdalena Basin potamodromous fish have two annual reproductive seasons: the
subienda in the first semester and the mitaca in the second semester. Both upstream migrations
are about 30 to 45 days long; after that, with the onset of the rainy season, fish spawn and remain
in the river (resident individuals) or start a downstream movement (the bajanza) to return to the
Magdalena floodplain lakes (nursery, shelter and feeding grounds). Due to its particular gonadal
development, at least the bocachico Prochilodus magdalenae and probably the comelón
Leporinus muyscorum are physiologically able to perform two annual migrations. In the
presence of dams or hydropower structures, fish are able to find alternative migration routes.
Some species should be recategorized in their migratory condition.
Keywords: freshwater migratory fish, flow regime, La Miel River, mark-recapture, migration
routes, migration speed and distance.
INTRODUCTION
Freshwater fisheries in the tropics are based on migratory fishes, mainly potamodromous
species. In general, they present highly seasonal spawning migration, associated with the flood
pulse of the rivers (Petrere, 1985; Lowe-McConnell, 1987; Carolsfeld et al., 2003). In fact,
reproduction of fish species in large Neotropical rivers, regardless of the strategy used, is highly
seasonal with spawning usually occurring in rising water level conditions, particularly among
migratory species (Agostinho et al., 2004). Although the elevation of hydrometric levels has an
overarching role, a set of additional factors such as temperature, photoperiod, moon phase and
total suspended solids in water acts as a trigger for gonad development and spawning (Vazzoler,
1996; Jiménez-Segura et al., 2010). The presence of dams and reservoirs intercepting rivers
changes the environmental information available for fish due to regulation of river discharge, as
1
Submitted to Journal of Fish Biology. Under the second revision.
29
Magdalena potamodromous migrations
well as the change in sediment and nutrients input downstream of the dam (Petts, 1984; Stevaux
et al., 2009), and changes the frequency, duration and magnitude of flood pulses (Payne, 1986).
These changes will influence the spawning behaviour, and affect the recruitment success of
some species and, in the long term, the community structure (Agostinho et al., 2001; Agostinho
et al., 2004; Sato et al., 2005).
All large rivers in northern South America show marked seasonality on the hydrograph; most
of them show a unimodal seasonal discharge pattern, but the Magdalena has a more complex
pattern including dual minima (February, October) (Lewis et al., 2006). In association with these
variations in water level, potamodromous fish spawn twice a year (Jiménez-Segura et al., 2010).
In the Magdalena River Basin, before the arrival of the rains, twice a year, potamodromous fish
swim hundreds of kilometres along the main rivers from the feeding grounds of the floodplain
in the lowlands to the Andean foothills, where they penetrate the tributaries until they encounter
obstacles that prevent them from continuing (Dahl, 1971). These species have very high
fecundity and spawn all their eggs at once in the open waters of the river channel when
conditions are suitable. Fertilized eggs are driven downstream by the water, while develop, hatch
and larvae enter the flood plains where they feed (Lucas & Baras, 2001; Sivasundar et al., 2001;
Jiménez-Segura et al., 2010).
Although the general pattern has been described and reproductive migrations undertaken by the
main commercial species of freshwater species are well recognized, information on
approximately 90% of migratory tropical fishes is based on little empirical evidence or landing
information (Lucas & Baras, 2001). The Middle Magdalena Basin has 129 fish species (Galvis
& Mojica, 2007); of these, 31 (24%) support small-scale fisheries (following Lasso et al., 2011)
and in turn 16 of them (12%) undergo reproductive migrations (12 of them listed in Usma et al.,
2009 and in Zapata & Usma, 2013). Until now, there has been no evidence to validate any of of
the two following hypotheses to explain the two spawning periods of large migratory fishes in
the Magdalena River Basin: H1: a fraction of the population of the migratory species may
reproduce during the first hydrological cycle in the year and the rest in the second one; and H2:
the same fish may reproduce twice a year (Jiménez-Segura et al., 2010). We believe that the
possible presence of two groups of one species reproducing separately in the same river would
imply the presence of at least two populations for potamodromous species in the basin, and thus
30
Magdalena potamodromous migrations
could probably indicate the start of a sympatric speciation process. In terms of conservation, the
validation of one of these hypotheses could help in the decision-making and the correct
allocation of resources and management efforts. Additionally, little is known about the distances
travelled, migration speed, origin and fate of individuals who undertake such movements, or the
behaviour of the species in regulated rivers. All this information can be used as a guide to
advance in the protection of migratory fish species and its key habitats for supporting the smallscale fisheries in the Magdalena River Basin.
La Miel River, located on the eastern slope of the western Andean Cordillera, is one of the most
important tributaries of the Magdalena River. It was dammed in 2002 for hydroelectric power,
affecting the hydrological cycles and, as a consequence, the migration, reproduction and
recruitment of large migratory fishes. Due to the presence of several human settlements, fishing
is an important activity throughout the year. To test the hypotheses above, we investigated
migration routes, duration, distances and, swimming velocities for migratory species that swim
up the Magdalena River and enter into La Miel River during the two reproductive periods of the
basin. As potamodromous fish in the Magdalena Basin support artisanal fisheries along the
whole basin, it was expected that tagged fish recoveries could help to approach a general scope
of fish movements, including responses to the dam.
MATERIALS AND METHODS
Fish tagging
Fish were caught from April 2010 to February 2012 at six sampling stations: four in La Miel
River including the discharge tunnel (TF) of the Miel I hydropower plant and its two main
tributaries: the Manso and the Samaná (Figure 1). The mark and release of fishes was carried
out monthly mainly for 15 consecutive days during each of the rising water periods in February
(2011 and 2012) and August (2010 and 2011) that correspond with the two upstream fish
reproductive migrations, called locally subienda and mitaca, and also over five consecutive days
(April 2010–April 2011). Fish were caught by fishermen using cast nets and kept in plastic tanks
with water renewed manually, and a few drops of Eugenol were used as an anaesthetic. When
the fishing activities were over, the fishermen went to one of the three gathering points in La
31
Magdalena potamodromous migrations
Miel River (at the discharge channel, TF; at la Cachasa, Cac; and San Miguel, SM) where the
fish were kept in a cage near the bank, in order to reduce the catching stress while it was marked.
At the gathering point the fish were weighed (g), measured (standard length, mm), tagged and
released. The tag was made of a small plastic tube containing a small piece of numbered rolled
paper with instructions for fishermen. The tag was attached with braided fishing line between
the two last pterygiophores of the dorsal fin. To prevent infections an iodine solution was used
(Photography 2).
fishing
transport
storage
measuring
weighting
piercing
prophylaxis
tag fixing
tagged fish
Photography 2. Tagging methodology of potamodromous fish species in La Miel River
Basin.
32
Magdalena potamodromous migrations
As this was the first study of this type in the Magdalena River Basin, the tags included a ‘reward
for information’ statement and were labelled with a toll-free phone number and the information
necessary to obtain the reward. A headlamp, a jacket or a scholar kit was given to fishermen
reporting low-reward tags. During the telephone interview, the fishermen were asked for the tag
number, fish species, location and date of capture, length, and the fisherman address to send the
reward (hereinafter returned data).
Data analysis
The distance travelled by each individual was estimated using the “routes” tool of Google Earth
version 6.0.3.2197 (2010) and the travel or elapsed time was calculated using the date of the fish
tagging and the recaptured date reported by the fisherman. The swimming velocities were
calculated using the data mentioned above (km/day), and they were graphed in a scatter plot
versus the standard length of fish to evaluate the effect of size on swimming velocities. In terms
of the analysis, time and distance zero correspond to the moment and place of fish release after
tagging. Negative distances correspond to downstream movements, and positive to upstream
movements. Due to tagging method, all distances referred in the document correspond to net
movements.
RESULTS
The upstream migrations of the Magdalena River were composed mainly of Characiformes
(Table I). During the four migratory seasons monitored, the most important species in the
catches were characiforms: bocachico Prochilodus magdalenae (14,727 ind., 87.4%), comelón
Leporinus muyscorum (1,168 ind., 6.9%), pataló Ichthyoelephas longirostris (208 ind., 1.2%)
and viscaína Curimata mivartii (173 ind., 1.02%). Siluriforms just comprised 0.96% of the total
catches and represented 1.8% of the biomass (Table I, Figure 4).
33
Magdalena potamodromous migrations
Table 1. Numerical and biomass abundances during four migratory seasons (August 2010, February 2011, August 2011 and February
2012), for potamodromous species captured in La Miel River Basin, number of tagged individuals and recovered data of each species.
Species
Order
Brycon rubricauda Steindachner, 1879
Colossoma macropomum (Cuvier, 1816)
Curimata mivartii Steindachner, 1878
Cynopotamus magdalenae (Steindachner, 1879)
Ichthyoelephas longirostris (Steindachner, 1879)
Leporinus muyscorum Steindachner, 1901
Pimelodus blochii Valenciennes, 1840
Pimelodus grosskopfii Steindachner, 1879
Prochilodus magdalenae Steindachner, 1879
Pseudopimelodus bufonius Buitrago-Suárez & Burr, 2007
Pseudoplatystoma magdaleniatum Buitrago-Suárez &
Burr, 2007
Salminus affinis Steindachner, 1880
Sorubim cuspicaudus Littmann, Burr y Nass, 2000
Other non-migratory species
Total
Characiformes
Characiformes
Characiformes
Characiformes
Characiformes
Characiformes
Siluriformes
Siluriformes
Characiformes
Siluriformes
Siluriformes
Characiformes
Siluriformes
Abundance
Tagged Recaptured
N
% Biomass %
24
0.1
12.9
0.4
24
0
2
0
0.9
0
2
1
173
1
27.2
0.9
149
1
20
0.1
3.8
0.1
15
1
208
1.2
73.7
2.4
168
1
1,168
6.9 217.2
6.9
785
12
15
0.1
1.5
0
13
84
0.5
18.3
0.6
68
1
14,727 87.4 2647.4 84.7 7,960
157
8
0
1.9
0.1
7
0
14
0.1
20.3
0.7
16
0
73
42
290
16,847
0.4
0.2
1.7
100
36.8
14
50.8
3126.9
1.2
0.4
1.6
100
52
40
3
1
0
9,299
178
34
Potamodromous fish in Miel I surge chamber
Brycon rubricauda
Colossoma macropomum
Cynopotamus magdalenae
Curimata mivartii
Cyphocharax magdalenae
Ichthyoelephas longirostris
Leporinus muyscorum
Pimelodus blochii
Pimelodus grosskopfii
Prochilodus magdalenae
Figure 4. Potamodromous species captured and tagged in La Miel River during four migratory
seasons (August 2010, February 2011, August 2011 and February 2012).
35
Potamodromous fish in Miel I surge chamber
Pseudopimelodus bufonius
Pseudoplatystoma magdaleniatum
Salminus affinis
Sorubim cuspicaudus
Figure 4 (Continuation). Potamodromous species captured and tagged in La Miel River during
four migratory seasons (August 2010, February 2011, August 2011 and February 2012).
The importance of P. magdalenae was similar between the February migrations, subiendas, and
during the August migrations (Chi2(2,3)=1.0463; p=0.593), mitacas (2010 mitaca 84.4%; 2011
subienda 90.0%; 2011 mitaca 83.2%; and 2012 subienda 87.6%). The importance of the other
migratory species changed between seasons (Chi2(2,7)=819.5522; p=0.000), with the
characiforms L. muyscorum, picuda Salminus affinis and siluriforms capáz Pimelodus
grosskopfii, bagre rayado Pseudoplatystoma magdaleniatum and blanquillo Sorubim
cuspicaudus being most important during the subiendas, and I. longirostris, nicuro Pimelodus
blochii and C. mivartii during mitacas (Figure 5).
36
Potamodromous fish in Miel I surge chamber
14
Proportion of catch (%)
12
10
8
6
4
2
0
Aug 2010
Feb 2011
Aug 2011
Feb 2012
Brycon rubricauda
macropomum
Figure 5. Catches proportions of potamodromous
species during theColossoma
upstream
migrations of
Brycon rubricauda
Brycon rubricauda
Curimata mivartii
Colossoma macropomum
Brycon rubricauda
Colossoma
macropomum
Magdalena
River
Basin
in
La
Miel
River.
P.
magdalenae
is
excluded
but
note
that
the missing
Brycon rubricauda
CynopotamusBrycon
magdalenae
Curimata
mivartii
Colossoma macropomum
Curimata mivartii rubricauda
Brycon rubricauda
Colossoma
macropomum
Brycon
rubricauda
Ichthyoelephas
longirostris
Cynopotamus
magdalenae
proportion
100%
corresponds
to this species.
, Curimata
mivartii;
,Colossoma
Ichthyoelephas
macropomum
Curimata for
mivartii
Cynopotamus
magdalenae
Colossoma
macropomum
Curimata mivartii
Colossoma
macropomum
Leporinus muyscorum
Ichthyoelephas
longirostris
Curimata
mivartii
Cynopotamus magdalenae
Ichthyoelephas
longirostris
Curimata
mivartiimuyscorum;
Curimata
mivartii
longirostris;
,
Leporinus
,
Pimelodus
blochii;
,
Pimelodus
grosskopfii;
Cynopotamus
magdalenae
Pimelodus
blochii
Leporinus muyscorum
Cynopotamus magdalenae
Ichthyoelephas longirostris
Leporinus muyscorum
Cynopotamus magdalenae
Cynopotamus
magdalenae
Ichthyoelephas
longirostris
Pimelodus grosskopfii
blochii
longirostris
muyscorum
,Leporinus
Pseudoplatystoma
magdaleniatum;
,Pimelodus
Salminus
affinis;
,
Sorubim
cuspicaudus.
Pimelodus Ichthyoelephas
blochii
Ichthyoelephas
longirostris
Ichthyoelephas
longirostris
Leporinus
muyscorum
Pseudopimelodus bufonius
Pimelodus grosskopfii
Pimelodus blochii Leporinus muyscorum
Pimelodus grosskopfii
Pimelodus blochii
Pseudopimelodus bufonius
Pimelodus grosskopfii
Pseudoplatystoma Pseudopimelodus
magdaleniatum bufonius
Salminus affinis
Pseudoplatystoma magdaleniatum
Sorubim cuspicaudus
Salminus affinis
Other non-migratory
speciescuspicaudus
Sorubim
Leporinus muyscorum
Pimelodus Leporinus
grosskopfiimuyscorum
Pimelodus Pimelodus
blochii bufonius
Pseudoplatystoma
magdaleniatum
Pseudopimelodus
blochii
Pimelodus
blochii
Pseudopimelodus
bufonius
Pimelodus Pimelodus
grosskopfii
affinis
Pseudoplatystoma
magdaleniatum
grosskopfii Salminus
Pimelodus
grosskopfii
Pseudoplatystoma
magdaleniatum
Pseudopimelodus
bufonius bufonius
Pseudopimelodus
Sorubim cuspicaudus
Salminus
affinis
Pseudopimelodus bufonius
Salminus affinis
Pseudoplatystoma
magdaleniatum
Pseudoplatystoma
magdaleniatum
Other non-migratory
species
Sorubim
cuspicaudus
Pseudoplatystoma magdaleniatum
Sorubim cuspicaudus
Salminus species
affinis
Salminus
affinis
Other
non-migratory
Salminus affinis
Other non-migratory
species
Sorubim cuspicaudus
Sorubim cuspicaudus
Sorubim cuspicaudus
Other non-migratory species
Other non-migratory
species
Other non-migratory species
Tags were applied to 9,299 individuals from 13 potamodromous species of Characiformes and
Other non-migratory species
Siluriformes. Overall, there were 196 returned data (2.10% return rate), 18 of them presented
questionable or incomplete data, with the remaining 178 being used for the analysis (Table 2).
Most tags were applied during the upstream migrations (95.5%) and a small proportion out of
migratory seasons, during in the monthly samplings (4.5%). From the 178 recaptured
individuals, 175 were tagged during the upstream migrations, and the other three (1.6%) were
tagged during the downstream migration time (2010-April) so all recaptures are informative for
fish movements during migrations. Tags were recovered throughout the Middle Magdalena
Basin, including La Miel River and its tributaries, some tributaries of the Magdalena River,
floodplain lakes and channels, as in Cauca River tributaries, another big basin of Colombia,
including a recovery from the Chinchiná River, located in the Upper Cauca Basin (Figure 6,
Table 2).
37
Potamodromous fish in Miel I surge chamber
Figure 6. Fish recovery locations, each dot corresponds to one individual.
Most of the returns were in La Miel River Basin, downstream of the dam (130 individuals,
75.0%). Within this basin, most of the tagged fishes (41.5 %) were caught in the last 6 km of La
Miel River before it flows into the Magdalena River and at the end of the discharge tunnel of
the Miel I hydropower plant (12.5%). The other fish were recaptured at other points of the
Magdalena River Basin: 28 returned data (15.9%) came from the main channel of the Magdalena
River, seven (3.9%) from some tributaries of the Magdalena River, seven (3.8%) from ciénagas
(flood plain lakes) or connection channels to floodplain lakes, and two (1.1%) from tributaries
of the Cauca River. The latter reports occurred during 2010 ENSO cold (La Niña) cycle, which
resulted in big and long-lasting floods all over the basin (Table 2).
Individuals recaptured correspond to nine migratory species, including an exotic species (the
cachama Colossoma macropomum). The recovered individuals belong mostly to P. magdalenae
38
Potamodromous fish in Miel I surge chamber
(87.9%), and in decreasing order to L. muyscorum (6.9%), S. affinis (1.7%) and 0.6% of each
one of the other six species (Table 2, Figure 4), so most of the results and conclusions correspond
mainly to P. magdalenae and L. muyscorum.
Most of the captures were downstream of the tagging place (64.3% of returned data), 29.9%
were upstream and a small percentage (5.7% of returns) was captured in the same place as the
tagging occurred. If movements of c. 2 km upstream and downstream of the tagging site are
taken into account, however, 24.1% of the tagged fish were recaptured near the releasing place.
Table 2. Number of individuals recaptured in each tagging place, distance between release and
recapture sites and time (minimum and maximum) between release and recapture. Zero time
and distance correspond to the time and place of release. * Sites within La Miel River Basin.
Site of Recapture
La Miel River Basin (LMR)
Discharge channel*
Manso River*
Samaná River*
last six kilometres*
Magdalena River (MR)
Magdalena River Tributaries (MT)
Floodplain lakes or connections
(FP)
Cauca River (CR)
Cauca River Tributaries (CT)
Total
Recaptures
N
%
130
73.9
21
11.9
7
4
9
5.1
72
40.9
28
15.9
8
4.5
8
4.5
1
3
178
0.6
1.7
100
Time (days)
min
max
0
369
0
185
5
55
0
65
0
369
0
805
1
1015
45
974
Distance (km)
min
Max
0
41.2
0
29.4
0.77
17.5
5.54
22.35
0
41.2
1
283
17.8
130
69.8
902
22
0
410.5
732
902
342
664
0
1223
1223
On a temporal scale, 60.3% (105 individuals) were recaptured during the first month (31 days)
after release, which corresponds to the upstream migratory period; 30.5% (53 individuals) were
captured in the next three months (between 32 days and 122 days) after release, and 9.2% (16
individuals) of the returns occurred in periods up to 123 days.
Based on the recaptured site, tagged fish moved in two main geographic areas: 1) within La
Miel River Basin, including its tributaries, and 2) outside of La Miel River Basin (other points
in the Magdalena Basin) (Figure 3). In turn, using the elapsed time, the movements within La
39
Potamodromous fish in Miel I surge chamber
Miel River Basin (the former first group) can be subdivided into three groups: 1a) catches made
during the first 31 days, corresponding to individuals captured during the migratory period, so
most occurred within La Miel River Basin, either at the upper sampling stations (near the
discharge channel), within the tributaries (Manso and Samaná Rivers) or moving out of the basin
(in the last 6 kilometres, with downstream movements ranging between 2 and 41.2 km from the
site of release), 1b) catches between 32 and 129 days of release, which would be individuals
that after the reproductive season remain in backwater habitats of La Miel River (mouths of
creeks, or secondary river channels with low flow), known as resident individuals, and 1c)
catches >130 days (four months) after release. Within this group, we can find fish recovered
between 130 and 185 days (four to six months), which corresponds to fish tagged during a
migratory event and recaptured during the next upstream migratory season. This latter group
includes fish recaptured in the Magdalena flood plain (ciénagas La Represa and La Victoria),
in Magdalena tributaries (Negrito River), and in La Miel River Basin: in backwaters of La Miel
River and in the discharge channel (TF) of the Miel I hydropower plant. Of the last-named, three
of these reports correspond to fishes tagged in the discharge channel and in the surge chamber
of the Miel I hydropower plant, and recaptured in the discharge channel in the next migratory
season, which can be an evidence that supports the hypothesis that the same fish may migrate
twice a year.
The movements outside La Miel River Basin can be subdivided into two groups: 2a) fish
captured during the first 31 days after tagging (during the migratory season) in Magdalena River
tributaries (Negro River) or tributaries of the Cauca River (Chinchiná River), and 2b) fish
recaptured after 45 days after tagging (during the downstream migration) or more, in flood plain
lakes, channel-floodplain connections or their mouths and tributaries of the Magdalena River
(Nare River) (Figure 7).
Most of the tagged individuals were caught downstream of their tagging site, between zero and
60 days, making trips ranging between 1223 and 664 km for fish recaptured in the Cauca River
tributaries, between 17.8 and 130 km for fish that entered in the Magdalena tributaries (Negro
River and La Malena creeks, respectively) and between 69.8 and 410 km for fish that returned
to the flood plain area (captured in lakes or channels) (Table 2).
40
Potamodromous fish in Miel I surge chamber
150
0 - 31 days
32 - 122 days
> 123 days
0 - 31 days
> 32 days
1200
100
1000
50
0
800
Distance (km)
0
20
40
60
80
100
120
-50
600
-100
400
-150
200
Time (days)
0
0
200
400
600
800
1000
-200
-400
Figure 7. Distance travelled and elapsed time between release and recapture of P. magdalenae
tagged and released in La Miel River Basin. Time and distance zero correspond to the moment
and place of release. Positive and negative values for distance correspond to upstream and
downstream movements from the tagging place. Note that dots correspond to movements within
La Miel River Basin (group 1), and triangles to movements out of the La Miel River Basin
(group 2). Also, note that the entrance to tributaries occurred during the first 31 days (white
triangles) or after the reproductive period in the lowlands (positive grey triangles). The return
(downstream migration) to Magdalena floodplain occurred after 45 days (negative grey
triangles) as well as the entrance to tributaries in the floodplain (positive grey triangles). The
fish populations have a proportion of individuals that do not undergo migration (black dots),
named as resident individuals, and a proportion that actively migrates, performing two
migrations by year: in February and August (grey dots near the 200 days).
P. magdalenae was the species that carried out the longest trips. In 22 days an individual
travelled 1223 km, swimming at 55.6 km per day (Table 3). The species that did the second
longest trips was L. muyscorum with a downstream migration of 199 km to a Magdalena flood
plain lake (Ciénaga Bijá), followed by S. affinis, which travelled 130 km between La Miel River
and La Malena, a small creek of the Magdalena River (Puerto Berrío municipality), with a
swimming speed of 11.8 km per day.
The shortest net displacement was made by S. cuspicaudus. An individual was recaptured 27
days after being tagged, 770 m upstream of the release site, and it was released again by
fishermen (Table 3). An individual of P. grosskopfii was recaptured the day after being tagged;
it had travelled nearly 18 km downstream, leaving La Miel River and being recaptured entering
41
Potamodromous fish in Miel I surge chamber
into the Negro River (in front of the mouth of La Miel), so its travelling speed was 17.8 km per
day.
Finally, it is worth noting the reports of an individual of cachama or black tambaqui (C.
macropomum) that was captured very close to its tagging place (1 km upstream) but 31 days
after being tagged; of an individual of chango Cynopotamus magdalenae, recaptured 7
kilometres downstream of the tagging site, 10 days later (0.03 km per day); and although there
is no information about the capture date, or tag number, a fisherman reported a tagged individual
of I. longirostris caught in the Samaná River at 219 m.a.s.l., swimming upstream the Samaná
River at least 20.8 km from La Miel River. The scatter plot for swimming velocity (km/day)
versus the size of all recovered fish did not show any correlation (Figure 8).
60
Prochilodus magdalenae
Leporinus muyscorum
Saminus affinis
Curimata mivartii
Cynopothamus magdalenae
Swimming velocity (km/day)
50
40
30
20
10
0
140
160
180
200
220
240
260
280
300
320
340
360
Standard length (mm)
Figure 8. Swimming velocity and size of recaptured individuals of migratory fish species
tagged and released in La Miel River Basin.
42
Potamodromous fish in Miel I surge chamber
Table 3. Minimum, maximum and mean distance (in km) and estimation of swimming speed
(km/day) of migratory species tagged in La Miel River Basin.
1
1
1
12
Min.
1
10.9
7.3
0
Distance
Max.
Mean
1
1
10.9
10.9
7.3
7.3
198.6
26.2
1
20.8
20.8
20.8
1
157
3
1
17.8
0
24.4
0.8
17.8
1224
130
0.8
17.8
34.3
62.1
0.8
20.7
Species
N
Colossoma macropomum
Curimata mivartii
Cynopotamus magdalenae
Leporinus muyscorum
Ichthyoelephas
longirostris
Pimelodus grosskopfii
Prochilodus magdalenae
Salminus affinis
Sorubim cuspicaudus
General
Min.
0
0.3
0.7
0
Speed
Max. Mean
0
0
0.3
0.3
0.7
0.7
5.1
0.17
17.8
0
0.2
0
17.8
55.6
11.8
0
17.8
1.4
5.4
0
2.9
DISCUSSION
The recapture rate observed in this study was similar to that reported in literature. Although it
may be smaller than other ones, the period of time of the present work is smaller than those of
Antonio et al. (2007) in the upper Paraná River in Brazil, who obtained a recapture rate of 2.85%
over five years of research; Bonetto et al. (1981) in the Middle Paraná River in Argentina, who
obtained a rate of 2.73% over six years; and Makrakis et al. (2007), who obtained a rate of 5.2%
in the Upper Paraná River in Brazil, Paraguay and Argentina and in the Itaipú Reservoir over
nine years. Our recapture distribution inside La Miel River Basin reflects fishing pressure,
mainly where fish accumulate during migrations at the end of the discharge channel, and in the
last 6 kilometres of the river where small towns of fishermen are located (Reinoso-Flórez et al.,
2010). Nevertheless, recovering data of tagged fishes may be influenced by tag losses, nonreporting of catches and handling that-induced mortality during the tagging procedure.
The observed net movements (distance) during the reproductive seasons showed that during
“subienda” and “mitaca”, the residence time of migrant fish in La Miel River Basin ranged
between 30 and 45 days; after that period the downstream migration captures started. This time
lapse, the duration of the breeding season, must be associated with the final maturation of
43
Potamodromous fish in Miel I surge chamber
gonadal tissue and staging for environmental signals for spawning, which are related to changes
caused by the onset of the rainy season (Kapestky et al., 1978; Jiménez-Segura et al., 2010).
Ichthyoplankton density rises 30–33 days after the beginning of the rains in the Magdalena River
(Jiménez-Segura, 2007). The recaptures of tagged fishes in the lowlands started 45 days after
tagging; therefore, I believe that all tagged fishes recovered before that time may be “migratoryspawning fish”. Fish in this category were staging (tagged fishes recovered in La Miel River –
La Miel River group) or searching (tagged fish recovered outside of La Miel River – the
Magdalena Basin group) for a spawning site.
In the described migratory-spawning pattern, after spawning most potamodromous fish return
to shallow lakes in the flood plain (shelter, nursery and feeding habitats). Individuals of P.
magdalenae, L. muyscorum and S. affinis tagged in La Miel River were caught downstream in
the Magdalena River (between 68.8 and 203 km from the mouth of La Miel River). This
downstream movement (“bajanza”) occurred 45 days after tagging in La Miel River in both the
migratory seasons: first and second semester (Figure 9).
44
Potamodromous fish in Miel I surge chamber
Figure 9. Diagrammatic representation of migratory cycles of Magdalena potamodromous fish.
At least one portion of individuals of P. magdalenae and L. muyscorum is able to perform in the
same year two consecutive upstream migrations. The water flow in the discharge channel of the
Miel I hydropower plant (TF) attracts schools of fish that remain visible, grouped and easily
catchable during the migratory season, and after spawning season the schools disappear and no
fishes are seen. Fish of group 1c were tagged during a migration period in TF and caught in the
same place during the next migration, supporting the statement that the same fish may migrate
45
Potamodromous fish in Miel I surge chamber
twice a year. Even if these fish are residents of La Miel River, they aggregated with the
migratory fish during two consecutive migrations following their reproductive impulse. Due to
their synchronous oocyte development in two groups, P. magdalenae can be induced twice a
year, and after ovulation, individuals of this species kept in captivity require approximately three
months to reach final maturation and be suitable for a new hormonal induction (Atencio et al.,
2013). These findings indicate that the species is physiologically able to reproduce naturally
twice a year, thus supporting partially the second hypothesis proposed by Jiménez-Segura et al.
(2010) to explain the two spawning periods of the basin, and a third hypothesis is proposed.
Taking in mind that the subienda is performed by a greater number of individuals than the
mitaca, even when the species is physiologically able to spawn twice a year, just a fraction of
the population achieve this energetically costs display. Thus, Magdalena upstream migrations
are performed by the same population but just one fraction is able to perform both, subienda and
mitaca, consecutively. Further studies would be necessary to find out whether the other
potamodromous species adjust to the same hypothesis. Neotropical potamodromous fish fauna
typically spawn once a year on the rising limb of the hydrograph (Lewis et al., 2006), while in
the Magdalena River basin, with its dual minima, potamodromous fishes migrate and spawn
twice a year, as corroborated by ichthyoplankton densities reported by Jiménez-Segura et al.
(2010).
The Magdalena River potamodromous fish species may have both migratory and non-migratory
individuals, as reported for other migratory species (Northcote, 1978). Fishes in group 1b (La
Miel River Basin) are individuals that after their breeding season remain in La Miel River for
up to 200 days, using backwaters or slow-flow water habitats and mouths of small streams and
rivers. These individuals support the fisheries of the Lower Basin of La Miel River during the
whole year (Reinoso-Flórez et al., 2010), they are members of the resident population, and are
already recognized by the local fishermen as such. This would be a complementary explanation
of the second hypothesis for clarifying the migratory behaviour of the Magdalena River
potamodromous fish.
P. magdalenae is physiologically able to reproduce twice a year, migrating in the subienda and
the mitaca of the same year. This is only possible if the fish are in appropriate condition, so, if
the fish are underfed and their energy reserves are inadequate, they will not migrate until they
46
Potamodromous fish in Miel I surge chamber
allocate and store enough energy resources that allows them to bear the energy costs of migration
and maturation of gonads for reproduction. Although Northcote (1978) talked about
“populations”, we prefer to use “individuals” because this would be a transitory state, so those
fish will eventually become migrant, in accordance with their energy reserve.
We must highlight the capture of tagged fishes of P. magdalenae in the Upper Cauca River
basin. During the study period a succession of ENSO events occurred: "La Niña" 2008/09, "El
Niño" 2009/10 and again "La Niña" 2010/2011. This last La Niña ended around June of 2011.
The recapture of this individual occurred during the 2010 ENSO cold (La Niña) cycle, which
resulted in big and long-lasting floods all over the basin, with several terrestrial habitats flooded
at the lowlands. We believe that due to these conditions of very high connectivity fish was able
to perform what under different conditions would be a very long (distance and time) travel in a
record time, probably making several shortcuts that we can’t calculate. ENSO events are known
to result in increased dispersion of migratory species, and the increase in connectivity allows
colonization of more patches (Gubiani et al., 2007). For years, Colombian ichthyologists
believed that migratory fish are not able to reach the middle and upper zone of the Cauca River
due to natural barriers in the limits between the lower and the middle zone of the basin,
considering the Cauca (Dahl, 1971) and the Upper Cauca (Usma et al., 2009) as different
populations. Therefore, it was thought that these fish species had separate populations:
Magdalena and Cauca populations. In light of this hypothesis, a reservoir for hydropower
generation in the middle zone of the Cauca River is being constructed (349 km downstream of
the site where the tagged fish was caught). Consequently, the dam, at 225 m high and without
any fish pass facilities, will block the migration routes of, at least, the most important species
for the Colombian fisheries: the bocachico P. magdalenae. Even when the occurrence of these
long movements is probably low, it favours persistence through metapopulation dynamics
(Gubiani et al., 2007).
Although most of the potamodromous species of the Magdalena Basin are middle-sized, the
species showed different swimming distances and speeds. The lack of correlation between
swimming velocity and fish size is explained by the nature of the data, with most fish being
recovered a long time after their release, making the velocity less accurate. Further research is
necessary with radio tags.
47
Potamodromous fish in Miel I surge chamber
P. magdalenae, L. muyscorum and S. affinis are the species that performed the largest
movements. The distances covered by P. magdalenae indicate that the species should be
classified as a long-distance migratory species (migrations over 500 km), as documented for
other species of the genus Prochilodus (Godoy, 1972; Bonetto et al., 1981; Toledo et al., 1986;
Agostinho et al., 1994, among others), and not as a middle-distance migratory species as
reported (Usma et al., 2009; Zapata & Usma 2013). Similarly, L. muyscorum has been
categorized as a short migratory species (Usma et al., 2009; Zapata & Usma 2013); nevertheless,
assuming that individuals exhibit some degree of fidelity to the flood plain and if we estimate
round-trip distances, this species should be categorized as a middle-distance migratory species
as reported for Leporinus obtusidens in the Paraná (Bonetto et al., 1981) and Paraguay Rivers
(Bayley, 1973), performing movements between 100 and 400 km, respectively. Ichthyoelephas
longirostris should be categorized as a migratory species. This species is commonly reported by
fishermen to be able to swim and jump through great waterfalls, not surpassed by the bocachico,
P. magdalenae (Castro & Vari, 2003). However, Colombian ichthyologists have not recognized
this species as migratory (Usma et al., 2009; Mojica et al., 2012; Zapata & Usma, 2013).
Although the maximum speed reported in the present work seems to be very high, P. scrofa in
the Paraná River swims up to 43 km per day as maximum speed (Godoy, 1972), at an average
speed of 5–8 km per day (Godoy, 1972; Toledo et al., 1987), and P. platensis swims at an
average speed of 13.4 km per day (Bonetto et al., 1981). We believe that the swimming velocity
of P. magdalenae must be slower, but due to the hydrological conditions during the travel of
that individual, the fish probably swam very fast downstream from La Miel River, helped by the
high flows of the basin and then in the flooded lowlands made a shortcut between the Magdalena
and the Cauca rivers, making shorter the traveling time. Additionally, later in the Cauca, the
high flows helped in the upstream swimming while the obstacles are reduced.
The results for S. affinis show that the species performs shorter movements than those reported
for Salminus maxillosus Valenciennes 1850, which migrates between 400 and 850 km (Bayley,
1973 and Bonetto et al., 1981, respectively), and has a lower swimming velocity than the 21 km
per day reported by Godoy (1975). It is known that the maximum velocity of fish increases with
the size of the fish (Wootton, 1992) and that as swimming is an energetically costly form of
locomotion, larger fish may be more likely to undertake long-distance migrations than smaller
48
Potamodromous fish in Miel I surge chamber
fish because the former travel more efficiently than the latter (Roff, 1988). Thus, the body size
of both species, combined with the difference in basin areas, the Paraná Basin being bigger and
the Salminus from the Paraná being bigger than the Colombian species, could give as a result
longer distances and a major swimming capacity for S. maxillosus.
49
Potamodromous fish in Miel I surge chamber
CHAPTER 3: POTAMODROMOUS FISH IN A SURGE CHAMBER: THE CASE OF
MIEL I HYDROPOWER PLANT2
Abstract: One of the most obvious impacts of damming a river is the disruption of migratory
routes. However, the characteristics of the dam, the river and its fish fauna make impossible the
generalizations about the possible effects. Since the beginning of the operation Miel I
hydropower plant, it was detected the entrance of fish into the hydropower plant surge chamber
(through the discharge tunnel) from La Miel River. To determine the composition of the fish
and evaluate the potential effects on migration, for one year (April 2010-April 2011) adult
individuals were tagged and released and ichthyoplankton collections were made, both in the
surge chamber and in the discharge tunnel. Individuals of migratory and non-migratory species,
mainly piscivorous and detritus-scrapers were found. Individuals who entered into the surge
chamber were able to find quickly the exit through the restriction orifice and returned to the
main channel of La Miel River. The fish did not spawn in the hydropower plant structures. We
conclude that the surge chamber is not an absolute barrier to migration, but it is a staging habitat
for migrant individuals.
Key words: Hydropower plant, potamodromous fish, migratory routes, Magdalena River, tag
and recapture, ichthyoplankton.
INTRODUCTION
One of the most negative and well recognized environmental impacts caused by damming rivers
is the disruption of migration routes of fish, affecting the free movement between spawning,
early development and feeding areas (Larinier 2001, Ligon et al. 1995). However, the design
characteristics of the dam, the river and its fish fauna make impossible generalizations about
possible impacts of all dams. In general, the most common reports include injuries and fish
mortalities caused by the physical structure of the components of the dam (spillway and
2
Published as: López-Casas, S., L. F. Jiménez-Segura y C. M. Pérez-Gallego. 2014. Peces migratorios al interior
de una central hidroeléctrica: caso Miel I, cuenca del río Magdalena (Caldas-Antioquia), Colombia. Biota
Colombiana 15 (2): 26- 39.
50
Potamodromous fish in Miel I surge chamber
turbines), by the hydrodynamic conditions created during operation of the plant, and attracting
and fish kills by suffocation in the suction duct (Agostinho et al. 2007). The loss of fish in
hydroelectric projects has been little studied in South America, and even in North America
where it is considered a priority, reports are scarce and controversial (Agostinho et al. 2007).
Additionally, information on these events is treated "stealthy", which makes difficult an open
discussion to the understanding and mitigation of the problem.
In January 2003, after the start of the operation Miel I hydroelectric plant (December 2002), it
was detected the presence of fish in the Miel I hydropower plant surge chamber (Figure 3). The
first time this situation was observed, it coincided with the arrival of potamodromous fish from
the main channel of the Magdalena River. Migratory species: Bocachicos (Prochilodus
magdalenae), picudas (Salminus affinis) and moínos (Leporinus muyscorum), entered through
discharge tunnel and after swimming 4.1 km reached the surge chamber where they accumulated
(Ingetec SA 2004) (Photography 3).
Photography 3. Potamodromous fish accumulations in the discharge tunnel, and in the surge
chamber of Miel I hydropower plant during the second reproductive migration, mitaca, of
2010.
The entry of fish into hydropower plant structures was not foreseen neither in the previous
ichthyologic studies nor in the environmental impact studies. The baseline studies had
51
Potamodromous fish in Miel I surge chamber
contemplated that migratory fish would swim upstream through La Miel River to La Palmera
(11 km downstream of the dam), established as the natural limit of subienda, and eventually
some fish would swim and surpass that point and accumulate in the discharge tunnel
(Photography 3). Under no circumstances it was contemplated that fish would penetrate through
the discharge tunnel, nor that would swim into the surge chamber due to the water velocity and
lack of light, which added to the physical and chemical properties of water, especially for the
low dissolved oxygen concentration and presence of H2S, would be adverse to fish (Mojica &
Jiménez-Segura, 2001).
The fish passage through the discharge channel it had not been reported in Colombia for any
hydropower plant (Ingetec SA 2004). Therefore, at the time it was assumed that fish into the
surge chamber would not evacuate this place, as its instinct would lead them to remain there,
and in no case they would return to La Miel River, so fish would stay inside the chamber until
die (Mojica & Galvis, 2003).
To test the former hypotheses, fishing and mark-recapture experiments were performed. The
results presented above seek to answer the following questions: What is the composition of fish
species in the surge chamber of Miel I hydropower plant? There are individuals of migratory
species? What are the sizes, weights, condition factor the assemblage of these species within the
chamber? Are those individuals able to swim out of the surge chamber? How long do they
remain there? Do these species spawn within the structure?
MATERIALS AND METHODS
Data collection and sampling
Monthly samplings of fishing for mark-recapture were conducted from April 2010 until April
2011. Ichthyoplankton samples were taken from April 2010 to September 2011. For security
reasons, from October to December 2010 fishing and data collection were no possible. Due to
safety conditions of the hydropower plant, the sampling within the surge chamber was
performed in a maximum of three hours, in which the plant generated energy under experimental
conditions, with one turbine operating at minimum power (Photography 4). Sometimes, by order
52
Potamodromous fish in Miel I surge chamber
of the Centro Nacional de Despacho- CND, the period was lower, since the plant was required
for operation. During these periods, observed species within the cavern were registered.
Photography 4. Miel I surge chamber under experimental energy generation.
Fish tagging
Cast nets, gillnets and surrounding nets of different mesh openings, electrofishing and hooks
with live and dead bait were used into the surge chamber. Additionally, laser attraction was used
to maximize the effectiveness of different gear. Cast nets were used only for fishing in the exit
of the discharge tunnel (TF), (see Figure 2 and Photography 1). The fishing effort was restricted
to the time given by the hydropower generation.
Fish caught were kept in plastic tanks with an anaesthetic solution, water was renewed manually
and a few drops of Eugenol were dissolved in water to anaesthetized fish for weighting (g),
measuring (standard length, mm) and tagging. The tag was made of a small plastic tube
containing a small piece of numbered rolled paper with instructions for fishermen. The tag was
53
Potamodromous fish in Miel I surge chamber
attached with braided fishing line between the two last pterygiophores of the dorsal fin. To
prevent infections an iodine solution was used
Due to the security and availability of access to the surge chamber, the tagged fish received three
treatments: 1) To determine whether individuals entering the chamber were able to swim out
and return to La Miel River, fish caught into the surge chamber were tagged and released into
the chamber (April to September 2010). 2) Subsequently, due to poor results from January to
April 2011, individuals caught and tagged in the exit of the discharge tunnel (TF), were
transported to the surge chamber in plastic bags with water, Eugenol and oxygen. Once there,
fish were placed in a plastic bucket and “placed” in the water of the chamber, waiting until fish
were acclimated and swim out of the bucket on their own. 3) In order to verify if accumulated
fish in the discharge tunnel entered into the surge chamber, individuals caught in the discharge
tunnel were released in the discharge tunnel after tagged.
Fishing in discharge tunnel
Fishing in surge chamber
Fish releasing in surge chamber
Photography 5. Fishing and fish releasing in the discharge tunnel and surge tank of Miel I
hydropower plant.
Tags included a ‘reward for information’ statement and were labelled with a toll-free phone
number and the necessary information to obtain the reward. A headlamp, a jacket or a scholar
kit was given to fishermen reporting low-reward tags. During the telephone interview, the
54
Potamodromous fish in Miel I surge chamber
fishermen were asked for the tag number, fish species, location and date of capture, length, sex
and maturity of fish, and the address to which to send the reward.
Ichthyoplankton
For collecting ichthyoplankton, a conic net with an attached flow meter (General Oceanics 2030
mechanical flowmeter) was used. The net was 4 micrometres mesh size and 0.38 m in diameter
at its mouth. In both the discharge tunnel and the surge chamber, backflow filtering for one
minute at each sampling time, was performed. The sample was fixed and preserved with 96%
alcohol and transported to the laboratory.
In the laboratory, samples were revised with the stereoscope in order to detect the presence of
eggs or larvae.
Data analysis
With the information reported by fishermen for each individual, distance and elapsed time from
tagging to recapture was calculated. Releasing was assumed to be time and distance zero;
negative distances correspond to downward movements (downstream) and positive to upward
movements (upstream) from the point where individuals were released.
RESULTS
Fish species into the surge chamber
For the three fishing treatments, 943 individuals of eight species, five of which are migratory,
were captured in the surge chamber and the discharge channel (Table 1). Of the total, 13
individuals (five species) were captured and released into the surge chamber; 808 individuals
(three species) were captured and tagged in the discharge tunnel and released in the surge
chamber and 122 individuals (six species) were tagged and released in discharge tunnel (Table
4).
55
Potamodromous fish in Miel I surge chamber
Table 4. Number of fish caught by species in the surge chamber (CO), discharge tunnel (TF),
and captured in the discharge tunnel and released into surge chamber (TF / CO) for sampling
species. + Migratory species.
Species
Brycon rubricauda Steindachner, 1879 +
Ichthyoelephas longirostris (Steindachner, 1879) +
Leporellus vittatus (Valenciennes, 1850)
Leporinus muyscorum Steindachner, 1901 +
Prochilodus magdalenae Steindachner, 1879 +
Rhamdia quelen (Quoy y Gaimard, 1824)
Salminus affinis Steindachner, 1880 +
Trichomycterus sp
Total
Vernacular name
Mueluda
Pataló
Filipino, Corunta
Moíno
Bocachico
Guabina
Picuda
CO
2
7
TF
2
8
112
1
2
1
13
TF/CO
1
6
2
256
542
1
122
808
Total
3
15
2
264
654
1
3
1
943
During the six months in which fishing was performed into the surge chamber, five species of
fish, of which just one (Trichomycterus sp) is of small size, were recorded. The remaining four:
mueluda (Brycon rubricauda), pataló (Ichthyoelephas longirostris), guabina (Rhamdia quelen),
and picuda (Salminus affinis) species correspond to medium and large size.
Although they were not captured, many individuals of bocachico (P. magdalenae) were
observed within the surge chamber. During the migratory season, individuals of moíno (L.
muyscorum) and occasionally individuals of the family Pimelodidae, which for their
morphology could correspond to nicuro (Pimelodus blochii) or capáz (Pimelodus grosskopfii),
were observed.
Of all the species caught and observed, permanent visual presence of mueludas, picudas, patalós
and bocachicos were recorded.
Fish movements
In total, of the 943 individuals captured both in the discharge tunnel and in the surge chamber,
839 individuals were marked and 24 reports of recaptures were obtained, which corresponds to
2.8% of the total tagged fish. Most reports came from downstream of the discharge tunnel in the
La Miel River and Magdalena River. There was no recapture on the surge chamber (Figure 10,
Table 5).
56
Potamodromous fish in Miel I surge chamber
Figure 10. Recovery locations of fish tagged and released in the discharge tunnel and the surge
chamber of Miel I hydropower plant. Each dot corresponds to one individual.
Of recaptured individuals, 18 (75%) were bocachicos (P. magdalenae); five (20.8%) moínos (L.
muyscorum) and one was a corunta or filipino (L. vittatus); (Table 5). All released individuals
in both, the surge chamber and the discharge tunnel were recaptured downstream from their
place of release, with two exceptions: a bocachico (individual 999), and a moíno (individual
1179), which after leaving the chamber, performed an upstream movement to the dam, and
recaptured in La Miel river at Puente Hierro, upstream of the discharge tunnel.
57
Potamodromous fish in Miel I surge chamber
Table 5. Places of fish tagging and recapture. TF: Discharge tunnel; CO: Surge chamber;
LMRB: La Miel River Basin; MR: Magdalena River; CCC: Floodplain lakes or connection
channels.
No.
Tagging
Station
L. muyscorum
1179
TF/CO
P. magdalenae
999
TF/CO
P. magdalenae
P. magdalenae
P. magdalenae
P. magdalenae
P. magdalenae
P. magdalenae
L. muyscorum
P. magdalenae
P. magdalenae
P. magdalenae
P. magdalenae
L. muyscorum
P. magdalenae
L. muyscorum
1851
1875
3398
3238
3438
1762
4675
1016
3203
3429
3438
3173
3299
3199
TF
TF
TF
TF
TF
TF
TF/CO
TF/CO
TF
TF
TF
TF
TF/CO
TF
P. magdalenae
3242
TF
P. magdalenae
3374
TF
L. vittatus
P. magdalenae
1343
3133
TF
TF
P. magdalenae
1848
TF
L. muyscorum
4852
TF
P. magdalenae
P. magdalenae
4772
4816
TF/CO
TF/CO
Species
Recapture
Lugar
Station
La Miel River, between the dam and TF, upstream of
LMRB
TF
La Miel River, between the dam and TF, upstream of
LMRB
TF
La Miel River, 2 km downstream of TF
TF
La Miel River, 100 m downstream of TF
TF
La Miel River, 1 km downstream of TF
TF
La Miel River, 8 km downstream of TF
LMRB
La Miel River, 2 km downstream of TF
TF
La Miel River, 2 km downstream of TF
TF
La Miel River in TF
TF
La Miel River 41,2 km downstream of TF
LMRB
La Miel River, 6km downstream of TF
LMRB
La Miel River, 8 km downstream of TF
LMRB
La Miel River, 2 km downstream of TF
TF
La Miel River, 4 km downstream of TF
TF
La Miel River, 2 km downstream of TF
TF
La Miel River, 100 m downstream of TF
TF
La Pardo Creak, where it flows to La Miel River, 13
LMRB
km downstream of TF
Caño Vasconia, connection channel to the floodplain
CCC
lake Ciénaga de Palagua, in Puerto Boyacá (Boyacá)
La Miel River, 100 m downstream of TF
TF
La Miel River, 2 km downstream of TF
LMRB
Caño de la Vuelta Acuña, connection channel to a
CCC
floodplain lake or ciénaga, Cimitarra (Santander).
Magdalena River at Estación Pita, Puerto Triunfo
MR
Municipality
La Miel River, 2 km downstream of TF
LMRB
Magdalena River at Puerto Wilches (Santander)
MR
Most recaptures occurred near the discharge tunnel: 13 occurred within 3.5 km of the discharge
tunnel in La Miel River; seven between 3.5 and 40 km downstream from the site of release and
the other four over 40 km away from the release place (Table 6).
58
Potamodromous fish in Miel I surge chamber
Table 6. Distance travelled (km) and time (in days) elapsed between release and recapture of
individuals of migratory species tagged and released in Miel I discharge tunnel and surge
chamber. Time and distance zero corresponds to the moment of release. Negative distances
correspond to downward movements and positive distances to upward movements from their
releasing point. TF = Discharge tunnel, CO = Surge chamber, TF / CO = captured in discharge
tunnel and released in surge chamber, LMRB = La Miel River Basin, MR = Magdalena River;
CCC = Floodplain lakes or connection channels.
Species
Tagging
Recapture
No.
Station
Station
Distance
Time
L. muyscorum
1179
TF/CO
LMRB
5.1
0
P. magdalenae
999
TF/CO
LMRB
4.6
1
P. magdalenae
1851
TF
TF
-2
0
P. magdalenae
1875
TF
TF
-0.7
6
P. magdalenae
3398
TF
TF
-1
0
P. magdalenae
3238
TF
LMRB
-8
1
P. magdalenae
3438
TF
TF
-0.33
1
P. magdalenae
1762
TF
TF
-0.88
12
L. muyscorum
4675
TF/CO
TF
-4.1
0
P. magdalenae
1016
TF/CO
LMRB
-45.3
34
P. magdalenae
3203
TF
LMRB
-16.2
32
P. magdalenae
3429
TF
LMRB
-13.5
37
P. magdalenae
3438
TF
TF
-2
1
L. muyscorum
3173
TF
TF
-4
18
P. magdalenae
3299
TF/CO
TF
-1.5
0
L. muyscorum
3199
TF
TF
-0.33
26
P. magdalenae
3242
TF
LMRB
-13.5
32
P. magdalenae
3374
TF
CCC
-69.8
41
Leporellus vittatus
1343
TF
TF
-0.1
0
P. magdalenae
3133
TF
LMRB
-0.88
35
P. magdalenae +
1848
TF
CCC
-183.5
85
L. muyscorum +
4852
TF
MR
-60.9
70
P. magdalenae
4772
TF/CO
LMRB
-6.1
149
P. magdalenae
4816
TF/CO
MR
-283
805
In the temporal scale, almost half of the individuals (10 ind.) were recaptured the same day of
their release after traveling less than 4.6 km (Table 6).
The residence time of the individuals released into the surge chamber was between zero and one
day (Table 6), indicating that once there, migratory fish quickly find the restriction orifice and
quickly move up to the tunnel exit where usually start a downward movement (downstream).
Most individuals (11) released into the discharge tunnel, stayed close to their place of release
59
Potamodromous fish in Miel I surge chamber
(so it was considered that it was recaptured within that sampling station, up to 5 km) for periods
ranging between 0 and 35 days (individual 3133). Additionally, four individuals moved
downstream without leaving the River La Miel, for periods between 13 and 37 days (individuals
3242, 3429, 3203 and 1016).
In April and May of 2011, four individuals were recaptured in the Lower Magdalena Basin.
Recaptures came from floodplain-lake-connection-channels and from Magdalena River (No.
3374, No. 1848, No. 4852 River and No 4816). These individuals showed longer distances and
higher times intervals from its release (69.8, 183, 60.9 and 283 km respectively); (Figure 11,
Table 6), reaching Puerto Wilches municipality (Santander) 283 km downstream from the surge
chamber.
50
0
+
0
Distance (Km)
-50
Time (days)
50
100
150
750
800
850
*
-100
-150
*
-200
-250
-300
Figure 11. Distance and time between release and recapture of migratory species individuals
tagged and released in discharge tunnel and surge chamber. Note that + corresponds to the
individual No. 999 captured in Iron Bridge; and * correspond to individuals that after making a
downward movement in the La Miel river basin, and in Magdalena River, performed a posterior
lateral movement, entering through a connection creek to a floodplain-lake.
In ichthyoplankton sampling into the surge chamber and the discharge tunnel neither fish eggs
nor larvae were captured, indicating that fish do not use the surge tank as spawning habitat.
60
Potamodromous fish in Miel I surge chamber
DISCUSSION
Fish species into the surge chamber
Inside the surge chamber fishing gear presented low efficiency, this is due to the surge chamber
features. The chamber is 44.5 m height and when the hydropower plant operates just with one
turbine has a minimum depth of 28 m, so the fishing gear (cast nets and gillnets) do not reach
the bottom, which is a necessary condition for proper operation. Additionally, it is a
homogeneous environment where electrofishing and surrounding nets were useless, since these
fishing gears based its effectiveness in "paralize" and surround fish from shelter habitats, so in
the absence of environmental heterogeneity, proved ineffective.
Effectivity of fishing gears affected the results of species composition. Thus, the number of
species captured inside the surge chamber was low if compared with the total number of species
reported for the basin ensembles (100 species; Jimenez-Segura et al. 2014). Because of this, it
was not possible to determine the proportion of the populations present in the chamber in relation
to that reported from the basin, as well as other aspects of assemblage structure (size and weight
distribution).
Eight fish species were captured associated to Miel I hydropower plant structures (surge
chamber and discharge tunnel, five of which are migratory, all previously reported for La Miel
River Basin fish ensemble. Except Trichomycterus sp. All fish species in the surge chamber are
species medium and large sized, and with some economic importance, being the pataló, the
moíno and picuda the species of greatest commercial importance in the basin (Reinoso-Florez
et al. 2010), and guabina a species for subsistence. Draws attention the size of individuals
captured in the chamber, being higher than the minimum regulatory capture sizes, as well as the
average size for each species reported for the Lower La Miel River Basin (Reinoso-Flórez et al.,
2010). These individuals have reached reproductive age, and regardless of its size, in that
environment, whether temporary or permanently, there are resources that allow meet their
energetic requirements, which in turn should be higher than those of smaller fish.
Fish that inhabit permanently the Miel I surge chamber are piscivorous and detritivory-scrapers,
so it can make use of the limited resources available within the hydropower structure (detritus biofilm- from the walls, insects and fish). In general, according to the literature, the fish species
61
Potamodromous fish in Miel I surge chamber
found in surge chamber can be categorized mainly into two trophic guilds: (i) detritivorous with
scraper strategy, and (ii) piscivorous. Surge chamber trophic resources are limited and, as noted,
restricted to Diptera larvae and macroalgae (collected in ichthyoplankton net trawls), fish and
biofilm (e.g. fungi, bacteria) growing on the walls and other structures (gates) of the chamber,
in which it was possible to observe fish feeding.
Surge chamber may be a hostile habitat due to its low oxygen concentrations (unpublished data),
high hydraulic variability, absence of solar radiation and high environmental homogeneity
(Mojica & Jimenez-Segura 2001). For this reason, it seems strange that even in these conditions,
the fish remain inside the chamber and during the reproductive migrations may be permanently
observed at high densities. Although we can list now some of the fish species within the
chamber, we do not know what factor or factors limit the presence of the species in the chamber.
Several questions about the reasons that lead the fish to enter or remain there are now open:
what is the main obstacle for the entrance of fish species into the structure? Once inside, why
do the fish stay there? Are the food resources a limiting factor in the chamber? In the case of
piscivorous, could be the high density of prey an incentive to stay there? and what about other
trophic guilds? Although we did not make an analysis of stomach contents of captured fish, we
believe that the food resources could limit the residence time of the different species, so below
there are some statements and approaches that could guide future research and explain the
present findings.
Agostinho et al. (2007) state that in structures associated with hydropower plants where
migratory fish accumulation occurs, such as stairs, ramps and other transposition facilities,
migrant fish are vulnerable to predation. High environmental homogeneity and the state of
exhaustion of individuals, ensures favourable conditions for piscivorous species such as
Salminus and Brycon (Agostinho et al., 2007a; Agostinho et al., 2007b). However, an inspection
of stomach contents of fish found in the surge chamber would be necessary to confirm this
hypothesis.
The guabina (R. quelen) had also been reported associated with the discharge tunnel during
samplings in the hydropower plant in 2008, when it was captured through a ventilation shaft
that allow access the tunnel in its middle reaches (Jimenez-Segura et al., 2008 ). This species
has nocturnal habits (Maldonado-Ocampo et al., 2005), is an omnivore species with a tendency
62
Potamodromous fish in Miel I surge chamber
to carnivory (Rivas-Lara et al., 2010) and with a great plasticity in its diet (Maldonado-Ocampo
et al., 2005). The combination of these factors could explain the presence of this fish species in
the surge chamber. Insects, plant seeds and shellfish are part of the moíno diet (L. muyscorum)
and pimelodids (P. blochii and P. grosskopfii), which have been categorized as omnivores with
tendency to herbivory (Jimenez et al., 2010), and opportunistic omnivores (López-Casas &
Jimenez-Segura, 2007; Villa-Navarro, 2010), respectively. These food preferences could be
limiting the presence of these species, as these resources were not observed in the structure.
Fish movements
Although the rate of recaptures reported in this paper is low, it is similar to the reported by other
studies in larger time intervals. Thus, in the Parana River recaptures they were obtained 2.85%
of various species within five years (Antonio et al., 2007) and 5.2% for assembly, Pterodoras
granulosus over a period of nine years (Makrakis et al., 2007). These recaptures rates reflect the
high intensity of fishing, which is probably higher, as would be biased due to errors associated
with tag loss, the absence of reports of tagged individuals and possibly manipulation-induced
mortality.
Given the particular design of Miel I hydropower plant, differently from other dams, fish
accumulation does not occur downstream of the dam, since the turbinated water outlet
(discharge tunnel) is located 4.5 km downstream of the dam. The surge chamber constitutes the
most upstream points that potamodromous Magdalena River fish can reach. Fish enter into the
chamber attracted by water flow. Once inside the chamber fish cannot go any further. However,
time in the surge chamber can be short, as confirmed by the recapture of individuals at the Lower
La Miel River Basin and in the discharge tunnel. Fish, migratory and non-migratory, found
quickly the exit through the restriction orifice, returning to the main channel of La Miel River.
Since greater influx of individuals in surge chamber is associated with the two periods of
potamodromous migration registered for Magdalena Basin, and that they are associated with
spawning of these species (Jiménez-Segura et al., 2010), we believe that: 1) fish enter the surge
chamber attracted by water flow as in other structures of hydropower plants (Agostinho et al.,
2007). 2) Migratory individuals accumulate in the surge chamber due to its impossibility to
63
Potamodromous fish in Miel I surge chamber
continue their upstream movement (Ingetec S. A. 2004). 3) During low water in the Magdalena
River, corresponding to the period of reproductive migration, it is possible that the specimens
observed inside the chamber spend short periods of time making a "pause", for their later return
to La Miel main channel in search of the closest tributaries (Manso and Samaná rivers), which
have been identified as spawning grounds (University of Antioquia-Isagen, 2012). During
reproductive migration, the use of "staging areas" has been reported in natural environments
(Godinho & Kinard, 2006), in these areas migrant individuals (pre-spawning fish) remain near
potential spawning habitats. Although this behaviour has not been reported to hydropower
structures, the surge chamber could be used in this way, becoming a temporary stop area during
the reproductive period, with fish entering and leaving the structure permanently, however
further investigation would be required to test these hypotheses. Monitoring the fish density
inside the chamber, may be done with equipment for counting fish ("fish counters") and the use
of radio tags, to obtain data of the exact movements of fish once they are outside the structure.
In addition, studies of ichthyoplankton densities in La Miel River Basin and its main tributaries
concluded that downstream of the dam, in Puente Hierro (where riverbed is almost dry, flowing
just with rain and discharge from small tributaries), in the discharge tunnel and in Cachasa
(CAC) are not spawning habitats for the Magdalena potamodromous species. In the other hand,
the non-regulated tributaries, both Manso and Samaná rivers are reported as the main spawning
areas of the basin (Moreno et al., 2013), showing that after blocking migratory routes fish are
able to find alternative routes and thus the importance of non-regulated rivers for maintaining
populations (Antonio et al. 2007).
The recapture of fish tagged in the surge chamber after the reproductive migration period
occurred in two main areas: within La Miel River Basin and outside La Miel River Basin this is
in floodplain lakes or connection channels, between the Magdalena River and the lakes. In
general, for fish two non-spawning grounds have been identified in rivers: feeding habitats and
shelter habitat (Lucas & Baras, 2001). Recaptures of individuals in connection channels,
between the Magdalena River and the floodplain lakes (in April and May), correspond to the
downstream migration, the bajanza. After the reproductive season, fish return to the floodplains
in the Middle and Lower Magdalena Basin, where their shelter and feeding habitats are located
(Kapestky, 1978; Jimenez-Segura et al., 2010), so those individuals report longer times and
64
Potamodromous fish in Miel I surge chamber
travelled distances from the moment of their release. According to the reproductive patterns
reported for Magdalena potamodromous species in the previous chapter and in Kapestky (1978)
and Jiménez-Segura et al. (2010), after spawning, most individuals return to the floodplain lakes,
however some remain in La Miel River, so for those individuals, once the reproductive season
ends, La Miel River could be considered as a feeding habitat. Due to the little floodplain
development, it is unlikely that can be considered a shelter habitat similar to those found in the
Lower Magdalena Basin.
Jiménez-Segura et al. (2008) report to have observed within the surge chamber fish activities
associated with Characiformes courtship and spawning behaviour. However, according to
ichthyoplankton sampling results, fish are not spawning in neither the surge chamber nor the
discharge tunnel. Additionally, Moreno-Arias et al. (2013) reported that under the dam, in the
stretch between TF and Manso River mouth there is no drift of eggs and larvae.
In conclusion, associated to Miel I hydropower plant discharge tunnel and surge chamber mainly
migratory species of both detritivorous-scraper and piscivorous behaviour, which can make use
of limited resources available into the hydropower plant (detritus -biofilm- from walls, insects
and fish), such as observed. The food availability and the absence of shelter habitats, may be
limiting factors for species entering into the chamber. Migratory fish and non-migratory entering
the chamber are able to quickly find the exit through the restriction orifice and return to the main
channel of La Miel River. Consequently, fish accumulation in that structure cannot be
considered as an entrapment, it is potentially short, and it seems to be associated with the length
of the migratory season, as well as waiting for the appropriate spawning and oocytes fertilization
conditions, despite which, the fish are not reproducing in the chamber nor in the discharge
tunnel. Additionally, it was concluded that shelter habitats of P. magdalenae and L. muyscorum
tagged in La Miel River, are downstream of Puerto Triunfo municipality, from Puerto Boyacá
(Boyacá) to Puerto Wilches (Santander) 283 km downstream of the surge chamber.
65
Hydropeaking effects in potamodromous fish based fisheries
CHAPTER 4: FISHING IN A REGULATED RIVER: HYDROPEAKING EFFECTS ON
CATCH PER UNIT EFFORT
Abstract: The flood regime is the most important force determining seasonality in Neotropical
rivers and their fisheries. Fish migrations and spawning are highly dependent on water level.
Potamodromous fish sustain fisheries in the Magdalena River Basin. After the construction of
the Pantágoras dam in La Miel River, at Middle Magdalena Basin, flow regimen changed and
local fishermen complained about a catches decrease. To evaluate the effect of water level
fluctuations (hydropeaking) by dam operation in the fishery catches, during six migratory
periods, the catch- per- unit- effort - CPUE, was recorded in different sampling sites in La Miel
River during different flow scenarios given by the water discharge of hydropower generation.
Fishermen captured 31,893 individuals (56 fish species). The most important species were
migratory Characiformes: Prochilodus magdalenae (87.0 %), Leporinus muyscorum (5.4%) and
Ichthyoelephas longirostris (2.5 %). Except for P. magdalenae, species composition and
abundance change through reproductive seasons. The generation of hydroelectric power altered
habitat features, affecting the effectiveness of fishing gear, fish density and fish distribution.
Differences between migratory seasons evidenced a positive trend with mean discharge during
migration. We conclude that changes in flow and water chemistry due to hydropower generation
could change the migration patterns, affecting CPUE; that flow regulation during migration may
change the attractiveness of the river, affecting the total CPUE not just during the migratory
season but also in the following years; thus affecting human populations that depends of fishing
as an economic activity.
Key words: Fisheries, flow regulation, dams, fishing gear efficiency, Magdalena Basin.
INTRODUCTION
In different systems worldwide, it has been recognized that flow is a major determinant of
physical habitat in streams, which in turn is a major determinant of biotic composition (Bunn
and Arthington, 2002). In the tropics, seasonality is mainly determined by wind patterns and
fluctuations in rainfall, and the largest seasonal change in inland waters is given by changes in
water level due to the sequence of wet and dry periods (Lowe-McConnell, 1987; Wootton,
1999). The biology and ecology of fish in large rivers are strongly linked to the annual
66
Hydropeaking effects in potamodromous fish based fisheries
hydrological regime in the main channel and the regular flooding of the associated floodplains,
affecting directly the use that fish make of available habitats and thus the fisheries (Welcomme,
1985; Junk et al., 1989).
Additionally, aquatic biota has developed life history strategies in direct response to natural flow
regimes (Bunn and Arthington, 2002). The reproduction of the fish species in large neotropical
rivers, regardless of the strategy used, is highly seasonal, with spawning occurring in rising
water conditions, particularly among potamodromous migratory species (Lucas & Baras, 2001;
Carolsfeld et al., 2003; Agostinho et al., 2004; Jiménez-Segura et al., 2010). Although the
elevation of hydrometric levels has a determinant role, a set of additional factors such as
temperature, photoperiod, moon phase and total suspended solids in water acts as a trigger for
gonad development and spawning (Vazzoler, 1996; Jiménez-Segura et al., 2010).
Since the abundance of long-distance migratory species it has been positively related to the
duration of floods and to connectivity in some South American rivers, extreme ENSOs (El Niño
Southern Oscillation) or a delay in the rains mainly affects the species with greater dependence
on the flooded habitats of the floodplain. These changes causes a reduction in the abundance of
long-distance migratory species (Fernandes et al., 2009). River flow regulation during the
migratory period may alter the seasonal and daily dynamics of migration, thereby altering the
population dynamics of involved fish species (Carolsfeld et al., 2003). Additionally, reduction
of the river discharge below the historic minimum discharge during the migratory period can
reduce the attractiveness of the river, and thus the number of spawning individuals entering into
it (Larinier, 2001). Consequently, changes in water level due to hydropower plant operation are
expected to influence migratory patterns during reproductive seasons, affecting the catch-perunit-effort-CPUE in river systems downstream the dams.
As in other tropical basins, fisheries in the Magdalena River Basin are sustained by
potamodromous fishes that undergoes reproductive migrations (Lucas & Baras, 2001;
Carolsfeld et al., 2003). La Miel River is one of the tributaries of the Magdalena, and, like this
basin, has a bimodal hydrological cycle. After the beginning of the hydropower plant Miel I
operation in 2002, the flow regime of La Miel River changed. Before the operation of the
hydropower plant, the river had two periods with high waters and two with low waters. After
the dam construction, the natural seasonal fluctuations has disappeared, and fluctuations that
67
Hydropeaking effects in potamodromous fish based fisheries
took place between seasons now can occur in one day or few hours. In 2007, artisanal fishermen
of La Miel River complained about a reduction of their catches due to the changes in the water
level.
To evaluate the impact caused in the fishery catches by water level fluctuations (hydropeaking),
due to the operation of Miel I hydropower plant, during six reproductive migratory periods
artisanal-fishery landing data were obtained downstream the Pantágoras dam along La Miel
River. Obtained data were analysed to answer the following questions: (i) Is there a relationship
between changes in water level by hydropeaking and the fishing CPUE?; (ii) Does hydropeaking
affect water quality and habitat availability for potamodromous fish in La Miel River Basin?, if
so, (iii) Does this changing affect the CPUE via changes in migratory patterns?
MATERIALS AND METHODS
Data collection and Analysis
The fishery landing data were obtained during six reproductive migratory periods: February and
August of 2008, August 2010, February and August 2011, and February 2012 that correspond
to the two annual spawning migrations, called locally subienda and mitaca. Fishery landing data
were from six sampling stations: four in La Miel River including the discharge tunnel (TF) of
the Miel I hydropower plant and its two main tributaries: the Manso and the Samaná (Figure 1).
We registered landing data for 25 consecutive days in 2008, and 15 consecutive days during all
other years. A team of two fishermen fished in each of the six sampling sites during different
flow levels (determined by the operation of Miel I hydropower plant). Fishing was carried out
using three cast nets of different mesh size according to the fishermen criteria. For each fishing
session we registered the species, weight, standard length, the fishing effort (number of cast net
throws), as well as the time spent at the fishing session.
For experimental design, we were advised of the water discharge for every hour of the day, thus
fishing was carried out according to the operation of Miel I hydropower plant: fishing and
landing data record was just performed if the flow remained stable for at least four consecutive
hours (4 h) to avoid flow fluctuations during fishing. Additionally, as Miel I power plant has
three Francis turbines, each one with a maximum discharge of 74 m3∙s-1, fishing events were
68
Hydropeaking effects in potamodromous fish based fisheries
categorized according to the discharged flow by the number of turbines. According to that,
fishing sessions that occurred on discharges until 74 m3∙s-1 were assigned to one turbine events;
fishing events between 75 and 148 m3∙s-1 were assigned to two turbines and events above 149
m3∙s-1 corresponded to three turbines. Hereinafter the fishing at each sampling station during
these periods of flow stability and known discharged flow are considered as a fishing sessions.
At each sampling station and at each fishing session we quantified the habitat heterogeneity
availability (if it was exposed or submersed) by assigning values to the type and size of
substrates and to the vegetation type at each sampling station (Table 7). At minimum flows,
when the river bed was exposed, negative values were given depending on the categories present
at each sampling station, and at maximum flows, when the river channel was all submersed,
positive values were given to the considered categories. Positive values were assumed to the
increase in the number of available habitat for fish and negative to the decrease, and were
summed to obtain a unique value. We also measured water level, wetted width of the river
(Stanley TLM 300 laser distance measurer), water deep (Garmin Fishfinder 250C), water
velocity taken as a single measure, in the middle of the river channel, 25 cm from the surface at
the point of maximum flow (General Oceanics 2030 mechanical flowmeter), and physical and
chemical variables (oxygen concentration, conductivity, temperature and pH).
Table 7. Categories for describing submerged and exposed habitat. Scores denote structural
complexity of each of the substrates, where one is the structurally least complex and 10 the most
complex.
Category
Mud
Sand
Shingle
Cobble
Boulder
Bedrock
Vegetation
Vegetation (roots)
Vegetation (tree trunks)
Vegetation (bamboo trunks)
Vegetation (shrubbery)
Vegetation (branches)
Dead vegetation
Description
Silts and clays (0.0006-0.0625 mm)
(0.0625-2 mm)
(4-20 mm)
(20-256 mm)
(256-4000 mm)
(bedrock)
Herbs, small creeping vegetation on the banks
Roots of trees, vines, shrubs, etc.., on the banks
Base of the trunk of trees located on the banks
Bamboo trunk bases on the banks
Trees lower than 2 m high
Tree branches falling over the river and submerged
Woody debris
Score
1
2
4
5
6
3
7
7
7
8
9
9
10
69
Hydropeaking effects in potamodromous fish based fisheries
These values were used as main matrix for a Principal Components Analysis – PCA in PcORd
5.0. As axes significance and retaining criteria for PCA we used the broken-stick distribution.
PCA axes with larger percentages of (accumulated) variance in relation to the broken-stick
variances are significant (Legendre and Legendre, 1998).
For individual fishing sessions yield was presented as iCPUE per fisher (kg per fisher·castnet
throw-1) and for daily or seasonal periods as total daily dCPUE (kg per day·total daily cast net
throws-1), and total seasonal sCPUE (kg per season·total seasonal cast net throws-1).
To test for differences in habitat characteristics along the basin at different flow events, the
scores of first axis of PCA (PCA1) were used in a two-way ANOVA as a the response
(dependent) variable, considering the flow (as a categorical variable: number of turbines given
by the discharged flow) and the sampling stations as factors or independent variables.
Subsequently, the scores of first axis of PCA were used as an independent variable to test for
differences in fishing sessions between seasons and sampling stations. Even when fishing
occurred in consecutive days, we considered fishing sessions as independent because La Miel
River is an open system and due to the nature of the upstream migrations, new fish arrive every
day into the river. Additionally the catches volume is small when compared with La Miel River
landings (estimated in 52 tons per year) and Magdalena River stock volume, thus it cannot affect
the next day catches. Nevertheless crossed correlations analysis were performed for daily and
seasonal catch per unit effort (dCPUE) to test this effect. To evaluate the relation between
changes in habitat due to Miel I hydropower plant operation and CPUE in each one of the fishing
sessions (iCPUE) we use PCA1 as independent variable.
We characterized the fishery at La Miel River Basin in terms of changes in yield and sCPUE
along the years studied and of the species that contributed most to the landings. We calculated
the frequency of occurrence (FO) of all species in each fishing session for each migration season
(number of times the species appeared in each migration/total number of fishing session for each
migratory season), and the daily frequency (DF) of the four most important species in the catches
(number of days the species were captured/number of working days). With these frequencies,
we examined differences in catches between different migratory seasons, and between days of
each migratory season.
70
Hydropeaking effects in potamodromous fish based fisheries
To evaluate the difference in sizes (standard length) of individuals of the most important
commercial species, we performed a nonparametric analysis of variance - Kruskal-Wallis
ANOVA using the STATISTICA 7.0 software.
To assess differences in CPUE between different flow scenarios grouped by the categories of
number of turbines, data were transformed (Log10 x +1) and tested the differences in iCPUE as
dependent variable, and the number of turbines in each session as categorical or grouping
variable using a one-way analysis of variance (ANOVA), and for test differences in iCPUE as
dependent variable, and the number of turbines and the sampling sites we performed a two-way
ANOVA using the STATISTICA 7.0 software.
RESULTS
During the six migratory seasons, fishermen captured 31,893 individuals of 56 fish species. The
main species caught in order of decreasing abundance were bocachico, Prochilodus magdalenae
Steindachner, 1879 (87.0 %), moíno Leporinus muyscorum Steindachner, 1901 (5.39 %), pataló
Ichthyoelephas longirostris (Steindachner, 1879) (2.48 %), viscaína Curimata mivartii
Steindachner, 1878 (0.9%), capáz Pimelodus grosskopfii Steindachner, 1879 (0.8%) and picuda
Salminus affinis Steindachner, 1880 (0.7%), which together composed approximately 97% of
the landings, all of them are migratory, and except the capáz (Siluriform), all are Characiforms.
Bocachico (P. magdalenae) was dominant during the whole study period, with values between
72.1% and 90.0%. All migratory seasons were different in its magnitude and abundance, and
showed daily fluctuations in biomass abundances and CPUE along the sampling period (Figure
12), being always higher in the subiendas than in the mitacas. The species composition changed
trough reproductive seasons.
71
Hydropeaking effects in potamodromous fish based fisheries
0.8
0.8
February 2008
August 2008
dCPUE (daily kg/trhow)
0.7
August 2010
February 2011
August 2011
February 2012
0.7
0.6
0.6
0.5
0.5
0.4
0.4
0.3
0.3
0.2
0.2
0.1
0.1
0.0
0.0
-1
1
3
5
7
9
11 13 15 17 19 21 23 25
0
1
2
3
4
5
6
7
8
9 10 11 12 13 14 15 16
Sampling days
Figure 12. Daily catch in La Miel River Basin in total dCPUE (daily kg/ daily throws) during
subienda (February) and mitaca (August).
We registered a total of 685 fishing sessions. Due to the differences in sampling duration in
which we registered the landings, and due to the variations in electric power production, the
number of fishing sessions with one, two or three turbines was different in each one of the
migratory sessions, whereby we obtained an unbalanced design: 295 (43%) sessions with one
turbine flow, 100 (15%) sessions with two turbines flow, and 290 (42%) sessions with three
turbines flow (Table 8). Standard error of yield (total kg per fishing session) was high when
compared with standard error of standardized landings of catch per unit effort (kg/cast net throw)
especially when the number of measurements was low (Table 8).
72
Hydropeaking effects in potamodromous fish based fisheries
Table 8. Mean values, standard errors and 95% confidence intervals of the biomass and catch
per unit effort of fishing sessions at La Miel River Basin, and total number of replicas per
number of turbines and migration period.
Migration
sub08
mit08
mit10
sub11
mit11
Turbines
Biomass (g)
iCPUE (kg/throw)
Mean
Std.Err.
-95%
95%
1
16.76
1.05
14.71
2
13.41
1.07
11.30
3
11.82
1.29
1
6.89
2
N
Mean
Std.Err.
-95%
95%
18.81
0.29
0.016
0.258
0.322
64
15.51
0.204
0.017
0.172
0.237
61
9.29
14.36
0.197
0.02
0.157
0.236
42
0.95
5.03
8.75
0.115
0.015
0.086
0.144
78
5.44
2.52
0.48
10.39
0.078
0.039
0.001
0.155
11
3
4.04
1.11
1.86
6.21
0.073
0.017
0.04
0.107
57
1
3.75
0.87
2.04
5.45
0.09
0.013
0.064
0.117
93
3
3.66
2.42
-1.08
8.41
0.088
0.038
0.014
0.161
12
1
11.50
2.42
6.76
16.25
0.209
0.038
0.135
0.282
12
3
13.86
0.96
11.97
15.74
0.22
0.015
0.191
0.249
76
1
6.44
1.21
4.07
8.81
0.096
0.019
0.059
0.133
48
2
7.93
1.75
4.50
11.35
0.108
0.027
0.055
0.162
23
3
8.31
1.97
4.43
12.18
0.118
0.031
0.057
0.178
18
2
13.14
3.74
5.79
20.49
0.222
0.058
0.108
0.336
5
3
9.57
0.91
7.79
11.35
0.145
0.014
0.117
0.173
85
2
2
1
sub12
Application of PCA to the habitat data showed that the first axis presented eigenvalue greater
than the Broken-stick eigenvalue: 3.02 (λ=3.387), therefore was retained and used for
interpretation. The spatial distribution of the scores of the PCA1 (30.79% explained variance)
revealed that habitat characteristics differed between flow scenarios and sampling site, with flow
related variables (water level, habitat availability, depth, oxygen concentration, etc.) in the
negative zone of the axis, and water chemistry variables (dissolved oxygen, pH and
conductivity) in the positive zone (Table 9). Nevertheless, regardless of the sampling site, the
habitat characteristics were different between flow scenarios (1, 2 or 3 turbines; F(0,05;10;
667)=5.4837;
p>0.001), except for Sam (Samaná River: tributary) and SM (San Miguel, lower La
Miel River channel), where the catches were independent of the Miel I hydropower plant
operation (Tukey HSD: p>0,05) mainly because Samaná River discharge eliminates the effect
of the hydroelectric (Figure 13).
73
Hydropeaking effects in potamodromous fish based fisheries
Table 9. Eigenvectors, eigenvalues, Broken-stick eigenvectors and percentage explanation of
the axes of axes 1 and 2 of the principal component analysis (PCA) applied to La Miel River
Basin habitat characteristics data matrix.
Eigenvector
Power
Turbines
Water level
Habitat
Oxygen concentration
Depth
Wetted width
Velocity
Temperature
Conductivity
pH
Eigenvalue
Broken-stick eigenvalue
Explanation percentage
Axis 1
-0.8466
-0.7989
-0.6794
-0.6505
-0.5449
-0.5358
-0.4236
-0.3641
0.2339
0.304
0.3233
3.387
3.02
30.794
Axis 2
0.0926
-0.0396
-0.3584
-0.0774
0.5108
-0.5174
0.4071
0.277
0.5208
0.197
-0.4774
1.454
2.02
13.214
The crossed correlations for seasonal and daily catch per unit effort (dCPUE) showed in general
positive trends, most of them showed no relation (r2<0.5), and most of them were not significant
(p>0.05), but some were significantly correlated (r2>0.5 and p<0.05; Table 10).
We did not found a relationship between the river flow during each of the fishing sessions and
catch per unit effort (kg·throw-1) even when considered separately by sampling site, or between
catch per unit effort and turbine discharge flow during the fishing session. There was also no
relationship between the water level nor river flow in each sampling site during each of fishing
sessions with the daily frequency of the most important species (DF) neither for frequency of
occurrence of all species (FO) in the catches (r2 <0.1).
74
Hydropeaking effects in potamodromous fish based fisheries
Table 10. Crossed correlations of daily catch per unit effort (dCPUE) between pair of consecutive
sampling days for all the assessed migratory periods. Note that sampling in 2010, 2011 and 2012
were of 15 consecutive days, while 2008 were of 25 consecutive days.
Day
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
r2
0.1069
0.1159
0.1076
0.0781
0.3249
0.1029
0.0909
0.0406
0.2512
0.3764
0.6670
0.1181
0.3457
0.2461
0.6052
0.6166
0.0888
0.0890
0.9283
0.5721
0.1409
0.2577
0.0488
0.1850
P
0.05160
0.04220
0.05080
0.09880
0.00030
0.05640
0.07400
0.23870
0.00180
0.00007
0.00000
0.04020
0.00020
0.00210
0.00290
0.00250
0.34690
0.34630
0.00000
0.00440
0.22920
0.09210
0.49000
0.16290
Equation
Day2 = 0.0938+0.2512*x
Day3 = 0.0924+0.3095*x
Day4 = 0.0759+0.2314*x
Day5 = 0.0815+0.4008*x
Day6 = 0.0681+0.7311*x
Day7 = 0.0933+0.2528*x
Day8 = 0.0991+0.2669*x
Day9 = 0.0993+0.2856*x
Day10 = 0.0939+0.3792*x
Day11 = 0.0491+0.8967*x
Day12 = -0.0157+1.1906*x
Day13 = 0.0933+0.1193*x
Day14 = 0.0186+0.6989*x
Day15 = 0.059+0.638*x
Day16 = 0.0348+0.4473*x
Day17 = 0.0191+0.9389*x
Day18 = 0.0589+0.3375*x
Day19 = 0.1246+0.4905*x
Day20 = -0.017+0.9593*x
Day21 = 0.0605+0.6898*x
Day22 = 0.0499+0.1046*x
Day23 = 0.0321+0.5328*x
Day24 = 0.0664+0.6272*x
Day25 = 0.0714+0.2908*x
75
Hydropeaking effects in potamodromous fish based fisheries
Figure 13. Average values of the first axis of Principal component analysis (PCA1) of sampling
stations in La Miel River Basin during one, two or three turbines flow discharge scenarios. The
vertical bars denote 0.95 confidence intervals. ANOVA: F(10, 667) =21.971; p=0.00.
However, we found that mean daily discharge from hydropower generation (turbines flow)
during the migration showed a positive trend with the total CPUE (tCPUE) during the entire
sampling period (Figure 14). Although the relationship was not significant (p> 0.05), when data
was linearized, the relationship accounts 63% of the data variation (r2 = 0.63).
76
Hydropeaking effects in potamodromous fish based fisheries
Figure 14. Scatterplot of mean daily discharge from Miel I hydropower generation (turbines
flow) and the total CPUE in La Miel River Basin during six migratory seasons (February and
August of 2008, August 2010, February and August 2011, and February 2012). Log 10 CPUE
= -2.0523 + 0.597·Log 10 Discharge (r2 = 0.63; p = 0.0601).
We found a relationship between yield (kg) and catch per unit effort (iCPUE: kg·throw-1) of
each of the fishing sessions and the scores of the first axis of the principal component analysis
(PCA1). In the ordination graph, fishing sessions showed a gradient across the PCA1 according
with the number of turbines that were operating during the fishing activity (Figure 15). These
differences in iCPUE were significant for the interaction between the sampling site and the
number of turbines (F
(10, 667)
= 2.5293; p = 0.005; Figure 16). The interaction significance is
mainly based in differences between sampling stations (F (5, 667) = 3.7012; p = 0.002).
77
Hydropeaking effects in potamodromous fish based fisheries
Figure 15. Scatterplot of iCPUE and habitat features (first axis of the principal components
analysis: PCA1) during each fishing session during subiendas and mitacas in La Miel River
Basin.
0.35
0.30
1 turbine
2 turbines
3 turbines
F(10, 667)=2.5293; p=0.0054
iCPUE (kg/throw)
0.25
0.20
0.15
0.10
0.05
0.00
-0.05
TF
Pal
Man
Cac
Sam
SM
sampling station
Figure 16. Mean catch per unit effort (iCPUE) by number of turbines during the fishing activity
in the six sampling stations of La Miel River Basin (see Figure 1: TF, Discharge tunnel; Pal, La
Miel River at Palmera; Man, Manso River; Cac, La Miel River at La Cachasa; Sam, Samaná
River and SM, La Miel River at San Miguel). Vertical bars denote +/- standard errors.
78
Hydropeaking effects in potamodromous fish based fisheries
Catch per unite effort (iCPUE) differed among migratory seasons (F
(2, 670)
= 40.4909,
p<0.0001). We observed that the mean catch per unit effort (kg/throw) during the migrations of
2008 and subienda of 2012, showed a negative trend with the number of turbines, resulting in
higher average catches in one turbine fishing sessions, and lower in the two and three turbines
respectively. By contrast, during the migrations of 2011 the average catches showed a positive
relationship, reporting higher biomass in the three turbines fishing sessions (Figure 17), there
were no significant differences for the interaction between the number of turbines and migration
season (F (14, 1338) = 1.1772, p = 0.28645; Figure 17).
0.4
F(14, 1338)=1,1772; p=0,28645
iCPUE (kg/throw)
0.3
0.2
0.1
0.0
1 turbine
2 turbines
3 turbines
-0.1
sub08
mit08
mit10
sub11
mit11
sub12
migratory seasson
Figure 17. Catch per unit effort (iCPUE) during subiendas and mitacas in La Miel River Basin,
by number of turbines during the fishing. Vertical bars denote 0.95 confidence intervals. Some
means are not estimable.
DISCUSSION
The assessment of habitat features and CPUE during six migratory seasons allowed the
identification of the effects of the hydrological regulation on the fish catches in La Miel River
Basin. The catches (CPUE) was related to the operation of Miel I hydropower plant. These
79
Hydropeaking effects in potamodromous fish based fisheries
variations can be attributed to changes in the effectiveness of fishing gear used by fishermen,
being more effective at low flows, and to a reduction on the attractiveness of the river for
migrating fish, affecting the total CPUE.
Operation of Miel I hydropower plant and the amount of energy it produces (generation with
one, two or three turbines), during fishing activity affected habitat features, mainly in its features
related to flow. Hydropower discharge directly affects the river volume, leading to changes in
water level (hydro-peaking), flow velocity, depth and wetted width of the river, which in turn
affected directly fish habitat availability. During low energy production (low water levels) the
flow of the river through its main channel is slow, exposing woody debris, sandy and pebble
bars and beaches, leading the fish to concentrate in a low number of suitable habitats (Murchie
et al., 2008; García et al., 2011), increasing in this way the fish density. On the contrary, during
high-energy production water levels are high, the river is deeper and flows faster, it spills out of
the main channel and it floods bars and lateral beaches, causing lower fish densities.
Cast nets are the main fishing gear used in La Miel River Basin. These nets, cast from the shore
or boat, catch the fish by falling and closing on them, reason why their use is usually restricted
to shallow waters (Nédélec and Prado, 1990). Thus, when used in high water level scenarios
(deeper habitats), the cast nets cannot reach the bottom, being lifted by the force of water,
leading to a decrease in the effectiveness of the fishing gear.
In the Magdalena River Basin potamodromous fish upstream movements are related to
reproductive migrations. Twice a year, fish migrate from the lower floodplains of the basin,
swimming upstream throughout the main river channel; entering into the tributaries in the
middle and upper basin searching for suitable spawning areas; reproduce at the beginning of the
flooding season to assure that their larvae enter into the floodplain when the river spill-out; and
their larvae drift to the floodplain lakes for feeding and growing (Kapestky et al., 1978;
Valderrama & Zarate 1989; Jiménez-Segura et al., 2010).
From an evolutionary perspective, evolution of many migratory patterns may also be the result
of reproductive adults placing their eggs in habitats in which the early survival and growth of
their offspring are maximized (Dodson, 1997). In river – floodplain systems, water level is a
proximal spawning factor (Jiménez-Segura et al., 2010), and the dynamics of flowing water are
80
Hydropeaking effects in potamodromous fish based fisheries
fundamental to oocyte fertilization, floatability and drifting, by the time water levels rise,
hydrated eggs drift along the river and spill onto the floodplain, where they complete its
development (Godoy, 1975). Added to that, spawning is coordinated in time and space with
conditions that favour early life history stages, so stochastic fluctuations in these conditions may
generate variations in reproductive success among individuals, as well as causing variations in
population size (Dodson, 1997), which can explain why it has been reported that large migratory
fishes do not spawn when the river water level is stable or decreasing (Godoy, 1975).
Nevertheless, fish can visit their spawning grounds independently of river discharge (Godinho
& Kynard, 2006). Changes in species composition added to annual variations in abundance
through migrations could be the result of differential spawning flow requirements.
Even when some crossed correlations were positive significant correlations for dCPUE we
believe that these correlations are spurious and they do not indicate pseudoreplication but are
related with the nature of upstream migrations. As mentioned above, Magdalena upstream
migrations are pulsating and abundance in the river seems to be related to the attractiveness of
the river for migrant individuals coming from Magdalena River. In reproductive migrations, fish
response to stimuli and these stimuli modulate the number of fish in La Miel River, so if the
stimuli are adequate, the fish input into La Miel River may be high, on the other hand, if the
stimuli aren’t appropriated may be low. Thus, the exhibited correlations among dCPUE of
consecutive days are the result of similar conditions (stimuli) for fish: when a bad fishing day
occurs, it is highly possible that the next day be also a bad fishing day. On the other hand, when
a good fishing day happens, it is highly probable that the next day behave in the same way,
causing correlations. Additionally, due to the nature of Magdalena River fish migrations and the
size of Magdalena stock, in greater or lesser extent, new fish arrive every day to La Miel River
from the Magdalena River, nullifying the possible effect in the catch caused by the catch of the
day before. This is also evidenced by the absence of a negative trend in the catches over sampling
time. Summarizing, we believe that the correlations have a biological meaning and not a
statistical (pseudo-replication) interpretation. However, it would not hurt to say that the
independence of fishing sessions is a ghost that has to be always in mind when ecological
research is made and that could be minimized for further research with a new sampling design,
for example with samples with a day in between.
81
Hydropeaking effects in potamodromous fish based fisheries
The operation of hydropower plant to attend energy demands during the whole migration season
affects the total CPUE in La Miel River Basin. Water releasing by high energy production during
this period means sustained high water levels (high average discharge) throughout the month,
and vice versa, water retention (low energy production) during the season means sustained low
water levels (low average discharge). Taking in mind that migratory - spawning fish were
dominant in La Miel River Basin fisheries, accounting nearly the 98% of landings, the
fluctuation of the river discharge dependent on the energy demand promoted non-natural
variation which reflex on the attractiveness of the river, and thus the number of spawning
individuals entering into it from the Magdalena, as it has been probed for other riverine systems
(Larinier, 2001), affecting the CPUE.
Energy production and increasing in the river discharge were related to the positive axis of
PCA1, indicating changes in chemical features of the river, mainly on pH, conductivity and
temperature, as well as changes in water level. For Magdalena potamodromous fish it is known
that small variations in the interaction of variables such as conductivity, water level,
temperature, between others, act as triggers for physiological and behavioural processes related
to reproduction (Jimenez-Segura et al., 2010). Consequently, changes in the chemical
characteristics of the water associated with the operation of the power plant could turn La Miel
River and/or its tributaries, more or less attractive to migrant individuals, effecting fish
migrations patterns and the CPUE in La Miel River Basin.
The catch per unit effort - CPUE fluctuated spatially and temporally during the six migratory
periods. In temporal scale, variations are related to the pulsing fluctuations proper of migratory
events. In Magdalena River, during low water levels, fish comes out from the floodplains in
several groups or schools, called locally “puntas”, which swim upstream and enter into
Magdalena tributaries (i.e. La Miel River Basin). Depending on the advance and movements of
these groups along the river and its tributaries the catches can fluctuate from one day to the next
one, as well as between sampling sites during the same fishing day. Thus, the “puntas” leave
the floodplains and swim up through the river, eventually one “punta” or part of one, enters into
La Miel River, and continues its upstream swimming, increasing the CPUE while crossing
through a sampling site, but decreasing the CPUE once it is gone.
82
Hydropeaking effects in potamodromous fish based fisheries
The spatial variation in the CPUE along the river basin is related to habitat variability, caused
by the water discharge of Miel I, and depends on peculiarities of sampling sites, which affects
the effectiveness of fishing gear and fish density. Thus, during both, mitaca and subienda, the
fishing sessions in sampling sites where the change in water level is not influenced by the turbine
flow (one, two or three turbines), that is Manso and Samaná rivers, are grouped by sampling site
along the first axis of the principal component analysis PCA1. While those sites that are
influenced by turbines discharge and located in La Miel River are scattered along the first
principal component axis, and all are grouped according to the number of turbines during each
fishing session. This trend is associated in the six sampling periods mainly with water velocity,
water level, changes in the habitat availability (emerged habitats are not available for fish),
conductivity, temperature and pH.
Because of the interaction of habitat variability and sampling sites features, it is not possible to
generalize about the optimal conditions for fisheries activities in the whole basin and it must be
taken into account for improvement of river management practices. The discharge tunnel (the
ending point for fish migration in La Miel River), is a deep habitat with strong and constant
current, where the cast nets are almost useless. Nevertheless, during the three turbines
discharges, the water level is so high that floods the exit platforms, turning these areas in a
highly suitable shallow slow running water habitat where the cast nets are very effective, and
where fish accumulates in high numbers and where are easily fished. Opposite situation occurs
in Samaná River, where the best fishing scenario occurs when the river has a low water level.
While in La Miel River at Palmera, Cachasa and San Miguel, and in Manso River it seems to be
the two turbines scenario: when the river spill out of its box and flood some shallow habitats
(Photography 6) that are used by fish to rest or feed (personal observations, Photography 7).
Nevertheless, if the flooding is higher, these habitats turn deeper, the river increases its width,
the fish dispersion is higher, the water velocity increases and the cast nets are less effective. This
idea reinforce how wrong is the assumption that rivers exist as a continuous gradient of physical
habitat, and that species will respond in a predictable and continuous manner (Vannote et al.,
1980), that is still commonly overlooked in some studies in regulated rivers (Murchie et al.,
2008).
83
Hydropeaking effects in potamodromous fish based fisheries
Photography 6. La Miel River at Cachasa during high water level (three turbines scenario) and
low water level (one turbine scenario).
Photography 7. Prochilodus magdalenae mouth (flannel mouth characiform) and mouth-prints
in submersed and exposed pebble-beach.
We can summarize the observed pattern in La Miel River Basin catches in two main effects: (i)
The operation of Miel I hydropower plant has a direct effect on fishing (CPUE), as it modifies
the physical characteristics of the habitat (mainly level, water depth and velocity), and thus,
changing the effectiveness of fishing gear used by fishermen (more effective at low water
levels), that together, with fish density modifies the iCPUE. (ii) Changes in water levels,
conductivity and pH, affect the river attractiveness for migratory fish, reducing the entry of
"puntas" or schools of fish when, during migration, the hydropower plant maintains a low flow
regimen.
Spatial and temporal change in habitat use by aquatic species in response to changes in discharge
and water level is typical in river systems (De Vocht & Baras, 2005). Taking in mind that small
84
Hydropeaking effects in potamodromous fish based fisheries
variations in the interaction of variables such as conductivity, water level, temperature, between
others, have been reported as triggers for physiological and behavioural processes related to
reproduction (Jimenez-Segura et al., 2010 ), and that potamodromous migratory-spawning fish
were dominant in La Miel River Basin fisheries, as its usual in South American basins (Castro
& Vary, 2003), we can conclude that: (i) changes in flow and water chemistry due to hydropower
generation could change the migration patterns, affecting iCPUE. (ii) Flow regulation (low
water levels) increases the schools access by fishing gears, but during migration reduces the
attractiveness of the river, and thus the number of spawning individuals entering into it, affecting
the total fish stock and consequently the sCPUE. (iii) Human riverine populations, which depend
on fishing as an economic activity and as a source of food, can be affected.
These effects are very interesting and deserve further analysis, especially if considering that dam
design features, the river, and its fish fauna make impossible the generalizations about possible
effects in fish habitat requirements and fisheries. Understanding these effects is essential for the
improvement of river management practices, especially if a balance is to be met between
supporting the economic interests of humans – energy producers and riverine livelihoods – and
the ecological requirements of fish (Gibbins & Acornley, 2000). As well as in rivers where
generation levels can simulate adequate conditions for both, human and fish.
85
ENSO cycles and potamodromous migrations
CHAPTER 5: ENSO CYCLES EFFECTS IN INLAND FISHERIES
POTAMODROMOUS MIGRATIONS IN TROPICAL SOUTH AMERICA
AND
Abstract: Tropical freshwater fisheries are based on migratory fish, manly potamodromous
species. In the Magdalena Basin, as in all the large basins of South America, they present highly
seasonal spawning migrations associated with the flood pulse of the rivers. Little effort has been
made to understand the relationship between artisanal fisheries and upstream migrations. To
explain some of the inter-annual fluctuations in catch associated with the ENSO effects in
fisheries, catches data were obtained in La Miel River, a middle size basin that belongs to the
Magdalena Basin, during six migratory periods between 2008 and 2012. Additionally, monthly
data of migratory fish abundance from the Manso River (tributary of La Miel River) from 20092012 were analysed. Our results points that fisheries in Magdalena River and its tributaries are
sustained by potamodromous species that arrive twice a year from the Middle and Lower
Magdalena Basin, the Prochilodus magdalenae being the most important species for fisheries.
Inter-annual fish abundance, fish biomass and migratory timing were related to regional rain
patterns and the changes in the hydrological conditions imposed by ENSO cycles. Additional to
the component of variance in catches explained by the inter-annual fluctuations in magnitude
and duration of flooding, the difference in abundance between the migrations of the same year,
i.e. subiendas and mitacas, can be explained by a physiological feature that allows that at least
one fraction of Prochilodus magdalenae population migrate twice per year, and modulate in this
way the magnitude of the Magdalena fish migrations.
Key words: Migratory species, artisanal fisheries, Prochilodus magdalenae, La Miel River,
ENSO cycles effects, potamodromous migrations.
INTRODUCTION
Freshwater fisheries in the tropics are based on migratory fish, mainly on potamodromous
species. In general, they present highly seasonal spawning migration, associated with the flood
pulse of the rivers (Petrere, 1985; Lowe-McConnell, 1987; Carolsfeld et al., 2003). Although
cyclical changes in day length and temperature are slight within the tropics compared with those
in temperate regions, periodic changes in wind and rainfall regimes do cause seasonality in most
86
ENSO cycles and potamodromous migrations
tropical ecosystems, in which seasonality is induced mainly by water level changes and the
subsequent expansion and contraction of the aquatic environment (Lowe-McConnell, 1987).
With the elevation of the water level, the newly flooded habitat offers extra space and food
(Goulding, 1980) which is usually reflected in growth (Lowe-McConnell, 1987) and recruitment
(Agostinho et al., 2004).
The hydroclimatology of tropical South America is strongly coupled with low-frequency largescale oceanic and atmospheric phenomena occurring over the Pacific and the Atlantic Oceans.
El Niño–Southern Oscillation (ENSO), in particular, affects climatic and hydrologic conditions
on timescales ranging from seasons to decades. With some regional differences in timing and
amplitude, tropical South America exhibits negative rainfall and streamflow anomalies in
association with the low–warm phase of the Southern Oscillation (El Niño), and positive
anomalies with the high–cold phase (La Niña) (Poveda & Mesa, 1997).
Impacts of ENSO-induced changes on various marine fisheries are well known, and include
among others changes in migration routes, recruitment and weight of some species (see for
example Mysak, 1986). On the other hand, despite the flow regime being regarded by many
aquatic ecologists to be the key driver of river and floodplain wetland ecosystems (Bunn and
Arthington, 2002), few studies explore the impact of the changes in hydrography associated with
ENSO and tropical fish populations (i.e. Smolders et al. 1999, Swales et al. 1999, Mol et al.
2000). These authors report strong effect on riverine fish production for migrating fish that have
their nursery grounds in the floodplains of undisturbed river systems (Smolders et al. 1999);
these include reduced catches due to El Niño-induced droughts (Swales et al. 1999), death of
some taxa, changes in landings, and failure to reproduce, or decreased reproductive success of
some species during El Niño years (Mol et al. 2000). Even in subtropical South American
lagoons and estuaries, where ENSO phenomenon has an inverse effect in hydroclimatology
(positive anomalies with El Niño, and negative anomalies with La Niña), similar effects have
been also reported for La Niña and El Niño, such as, having a strong influence on fish population
dynamics and assemblage structure of fish species living within and adjacent to estuarine
habitats (Garcia et al., 2001, 2003).
One of the most recognized patterns in potamodromous migrations that takes place in South
American rivers is the migration of species of the genus Prochilodus (Godoy 1972; Bayley
87
ENSO cycles and potamodromous migrations
1973; Lucas & Baras 2001; Carosfeld et al. 2003; Barletta et al. 2010). In the Magdalena basin,
potamodromous fish, such as Prochilodus species, have two annual reproductive seasons: the
subienda in the first semester and the mitaca in the second semester. Before the arrival of the
rains, potamodromous fish swim hundreds of kilometres along the main rivers from the feeding
grounds of the floodplain in the lowlands to the Andean foothills, and then move to the
tributaries until encountering obstacles that prevent them from continuing (Dahl 1971). These
species have very high fecundity and under appropriate conditions spawn all their eggs at once
in the open waters of the river channel. Fertilized eggs are driven downstream by the water,
where they develop and enter into the floodplains where the larvae feed (Lucas & Baras, 2001;
Sivasundar et al., 2001; Jiménez-Segura et al., 2010).
In Colombia, the present knowledge recognizes 106 freshwater migratory fish, 13 of them
inhabiting Magdalena Basin (Usma et al., 2009; Zapata & Usma, 2013). These species supports
local fisheries (Lasso et al., 2011), and perform upstream migrations twice a year: the first,
known locally as the subienda, is undertaken around December to March, while the mitaca takes
place from approximately July to September, (Dahl, 1971). Although, Magdalena River Basin
is the principal fluvial system of Colombia and is one of the basins with the highest number of
ichthyologic studies, little effort has been made to understand the relationship between the main
natural events that rule the artisanal fisheries in all the basin: the upstream migrations. Due to
the influence of ENSO cycles in precipitations and river discharge, may be expected to affect
catches via changes in fish population dynamics and ensembles structure. Our results show that
in Northern South America exists a strong relationship between artisanal fisheries and upstream
migrations, and that ENSO cycles have a major impact on migratory fish fauna, being
responsible for some of the inter-annual fluctuations in total catches, therefore affects fisheries
across the Magdalena Basin.
METHODS
Data collection and analysis
Fishing data were obtained downstream the Pantágoras dam during six reproductive migratory
periods (rising waters): February and August of 2008, August 2010, February and August 2011,
and February 2012 that correspond to the two annual fish spawning migrations, called locally
88
ENSO cycles and potamodromous migrations
subienda and mitaca. During those periods the catches of fishermen were registered for 25
consecutive days in 2008, and for 15 consecutive days during all other years. A team of two
fishermen fished using cast nets (three different mesh sizes) in each of the six sampling sites
during different flow levels (determined by the operation of Miel I hydropower plant). For each
fishing session we registered the species, weight, length (standard length), sex and maturity of
fish (immature or mature). As the determination was performed by fishermen, immature
individuals include undeveloped ovaries not containing visible maturing or mature eggs as well
as ripening individuals, and mature individuals include ripe and spawned individuals. Fishermen
were requested to register their fishing effort (number of cast net throws).
We characterized the experimental fishery at La Miel River Basin in terms of changes in CPUE
along the assessed years.
To corroborate the impact of migratory fish in the catches of La Miel River Basin, and its
dependence on these cyclical movements of Magdalena River fish, data of fishing on a monthly
basis (February-2009 to March-2012) of one of the sampling sites of La Miel River Basin
(Manso River), with constant effort (90 cast net throws with three different mesh sizes) was
used. With these data we plotted the total catch of migratory species in Manso River with the
mean monthly water level of Magdalena River at middle Magdalena Basin (Puerto Berrío
Municipality), and to determine the portion of the annual catches that is provided by catches
during the upstream migration periods, we calculated monthly percentage of catches, both
numerical and in biomass (kg), relative to the total catch for each year.
To evaluate the difference in sizes (standard length and total weight) of individuals performing
each migration, we performed a nonparametric analysis of variance - Kruskal-Wallis ANOVA
using the STATISTICA 7.0 software.
The mean multiannual (2002-2012) water level and standard deviation of Magdalena River was
calculated, and these values were used to calculate for each semester the minimum and
maximum water levels of the river (Mean water level ± SD), the number of days under the
minimum level, and over the maximum level.
89
ENSO cycles and potamodromous migrations
Finally, to test the effect of hydrological variations due to ENSO cycles in size and weight of
migratory individuals, we correlated the former values with the mean standard length (mm);
mean total weight (g); and of the Fulton’s condition factor (K=W/L3, where W = the weight of
the fish, and L is the standard length in centimetres) as an approximation to energetic reserves
measure; and the total CPUE (individuals/throw) of each assessed reproductive period. The
regressions were made without time lag, and with a time lag of six months and one year.
RESULTS
During the six migratory seasons, in a total of 685 fishing sessions, fishermen captured 31,893
individuals (11,500 individuals in 2008-subienda; 3636 individuals in 2008-mitaca; 1430
individuals in 2010-mitaca, 7338 individuals in 2011-subienda; 3598 individuals in 2011mitaca, and 4778 individuals in 2012-subienda) of 56 fish species (28 species in 2008-subienda
and 2010-mitaca; 27 species in 2008-mitaca and in 2011-subienda; 33 species in 2011-mitaca,
and 23 species in 2012-subienda).
The total yield was 6.556 t of fish represented in 2.561 t and 863.6 kg in the subienda and mitaca
of 2008 respectively, 392 kg caught during the 2010-mitaca, 1.2 t and 642 kg caught during
2011 subienda and mitaca, and 879 kg during the 2012-subienda (Figure 18). The highest catch
per unit effort in number of individuals was registered in the 2011-subienda, while the 2008subienda was the most important in biomass because even when in 2011 the fishermen reported
28.3% more catches than in 2008, the individuals of those migration were smaller (H ( 5, N= 31977)
=2516,734 p =0,000) and lighter (H ( 5, N= 31880) =2655,410 p =0,000) than those ones caught in
2008, this difference was clearly observable because due to the small size of the 2011 migrants
lots of them were able to escape thorough the cast nets.
From the total data sets analysed we registered 38,588 individuals of 51 species, from these, 21
species (38095 individuals) are commercial or have some economic profit, and 16 species
(38,034 individuals) are potamodromous species, being Characiformes the most common
species. In order of decreasing abundance were bocachico, Prochilodus magdalenae
Steindachner, 1879 (88.0 %), moíno Leporinus muyscorum Steindachner, 1901 (4.58 %), pataló
Ichthyoelephas longirostris (Steindachner, 1879) (2.47 %), viscaína Curimata mivartii
90
ENSO cycles and potamodromous migrations
Steindachner, 1878 (0.77%), capáz Pimelodus grosskopfii Steindachner, 1879 (0.68%) and
picuda Salminus affinis Steindachner, 1880 (0.59%), which together composed approximately
97.65% of the catches (Table 11). Bocachico (P. magdalenae) was dominant during the whole
study period, fluctuating between 86.53% and 90.91% among years (Figure 19). All migrations
were different in its magnitude and abundance, and showed daily fluctuations in biomass
abundances and CPUE along the sampling period, being always higher in the subiendas than in
the mitacas.
1.4
1.4
Numerical
Biomass
1.2
1.2
1.0
1.0
0.8
0.8
0.6
0.6
0.4
0.4
0.2
0.2
0.0
0.0
Feb08
Aug08
Aug10
Feb11
Aug11
Biomass (kg/throw)
Numerical (Ind/throw)
CPUE
Feb12
migration
Figure 18. Catch per unit effort for each of the assessed migrations in the lower basin of La
Miel River.
The number of migratory species present in the landings of each upstream migration was similar
over time and ranged between 11 and 13 species, totalling 16 potamodromous species of the 51
species caught by fishermen (Table 11).
Thus not just the potamodromous species composition varies over time, also the importance of
the migratory species was different between migratory seasons, being notorious the catch
91
ENSO cycles and potamodromous migrations
fluctuations of some of the commercial species such as L. muyscorum, I. longirostris, S. affinis
and C. mivartii (Figure 20).
92
ENSO cycles and potamodromous migrations
Table 11. Abundances and taxonomical classification of the species caught during the six assessed migratory seasons in the low La Miel
River Basin. Species in bold are recognized for their migratory habits.
Species
Vernacular name
Order
Family
Abundance
(n)
(%)
11
0.03
Acestrocephalus anomalus (Steindachner, 1880)
Chango
Characiformes
Characidae
Andinocara latifrons (Steindachner, 1878)
Mojarra azul
Perciformes
Cichlidae
3
0.01
Andinocara pulcher (Gill, 1858)
Mojarrita
Perciformes
Cichlidae
7
0.02
Apteronotus sp (Lacepède, 1800)
Yumbila
Perciformes
Apteronotidae
1
0.00
Astyanax fasciatus (Cuvier, 1819)
Sardina,tota coliamarrilla
Characiformes
Characidae
25
0.06
Astyanax magdalenae Eigenmann y Henn, 1916
Sardina, tota
Characiformes
Characidae
3
0.01
Astyanax spp
Tota coliroja
Characiformes
Characidae
5
0.01
Brycon moorei Steindachner, 1878
Dorada
Characiformes
Bryconidae
53
0.15
Brycon rubricauda Steindachner, 1879
Mueluda
Characiformes
Bryconidae
53
0.14
Bunocephalus colombianus Eigenmann, 1912
Matacaiman
Siluriformes
Aspredinidae
1
0.00
Caquetaia kraussii (Steindachner, 1879)
Perciformes
Cichlidae
9
0.02
Perciformes
Cichlidae
48
Chaetostoma spp
Mojarra amarilla
Mojarra negra o azul, mojarra
voladora
Cucha getona
Siluriformes
Loricariidae
89
0.23
Chaetostoma fischeri Steindachner, 1879
Cucha blanca o pintada
Siluriformes
Loricariidae
101
0.26
Chaetostoma leucomelas Eigenmann, 1918
Cucha getona
Siluriformes
Loricariidae
1
0.00
Chaetostoma milesi Fowler, 1941
Cucha getona
Siluriformes
Loricariidae
25
0.06
Cichlidae
Mojarrita
Perciformes
Cichlidae
3
0.01
Colossoma macropomum (Cuvier, 1816)
Cachama
Characiformes
Serrasalmidae
3
0.01
Creagrutus magdalenae Eigenmann, 1913
Tota
Characiformes
Characidae
1
0.00
Crossoloricaria variegata (Steindachner, 1879)
Cucha pitera
Siluriformes
Loricariidae
1
0.00
Curimata mivartii Steindachner, 1878
Vizcaína
Characiformes
Curimatidae
291
0.77
Cynopotamus magdalenae (Steindachner, 1879)
Chacha, cháchango
Characiformes
Characidae
30
0.08
Cyphocharax magdalenae (Steindachnner, 1878)
Campaniza
Characiformes
Curimatidae
3
0.01
Dasyloricaria filamentosa (Steindachner, 1878)
Cucha pitera
Siluriformes
Loricariidae
8
0.02
Dasyloricaria seminuda (Eigenmann & Vance, 1912)
Cucha pitera
Siluriformes
Loricariidae
1
0.00
Caquetaia umbrifera (Meek y Hildebrand, 1903)
0.12
93
ENSO cycles and potamodromous migrations
Geophagus steindachneri Eigenmann y Hildebrand, 1910
Mojarra jacho o lora
Perciformes
Cichlidae
Abundance
(n)
(%)
58
0.15
Hoplias malabaricus (Bloch, 1794)
Moncholo, ñaco, perro
Characiformes
Erythrinidae
13
0.03
Hypostomus spp Lacépède, 1803
Siluriformes
Loricariidae
1
0.00
Siluriformes
Loricariidae
48
Ichthyoelephas longirostris (Steindachner, 1879)
Cucho
Coroncoro, cucho Ramirez, cucho
sarco
Pataló, besote
Characiformes
Prochilodontidae
794
2.47
Lasciancistrus caucanus Eigenmann, 1912
Cucha Barbuda
Siluriformes
Loricariidae
2
0.01
Leporellus vittatus (Valenciennes, 1850)
Corunta, filipino, rallado, bonito
Characiformes
Anostomidae
23
0.06
Leporinus muyscorum Steindachner, 1901
Comelón, moíno
Characiformes
Anostomidae
1724
4.58
Loricariidae
Corroncho, cucha
Siluriformes
Loricariidae
20
0.05
Oreochromis niloticus (Linnaeus, 1758)
Tilapia
Perciformes
Cichlidae
1
0.00
Parodon suborbitalis Valenciennes, 1850
Mazorco
Characiformes
Characidae
5
0.01
Pimelodella spp Eigenmann & Eigenmann, 1888
Rengue
Siluriformes
Heptapteridae
1
0.00
Pimelodella chagresi (Steindachner, 1877)
Capitán
Siluriformes
Heptapteridae
1
0.00
Pimelodus blochii Valenciennes, 1840
Nicuro
Siluriformes
Pimelodidae
41
0.11
Pimelodus grosskopfii Steindachner, 1879
Capáz
Siluriformes
Pimelodidae
260
0.68
Pimelodus spp Lacépède, 1803
Pujón
Siluriformes
Pimelodidae
1
0.00
Potamotrygon magdalenae (Duméril, 1865)
Raya
Myliobatiformes
Potamotrigonidae
3
0.01
Prochilodus magdalenae Steindachner, 1879
Bocachico
Characiformes
Prochilodontidae
27827
88.57
Pseudopimelodus bufonius (Valenciennes, 1840)
Pseudoplatystoma magdaleniatum Buitrago-Suárez &
Burr, 2007
Rhamdia wagneri (Günther, 1868)
Bagre sapo
Siluriformes
Pimelodidae
8
0.02
Bagre, Pintado
Siluriformes
Pimelodidae
25
Guabina
Siluriformes
Heptapteridae
4
0.01
Salminus affinis Steindachner, 1880
Picuda
Characiformes
Bryconidae
225
0.59
Sorubim cuspicaudus Littmann, Burr y Nass, 2000
Blanquillo
Siluriformes
Pimelodidae
88
0.23
Spatuloricaria gymnogaster (Eigenmann & Vance, 1912)
Alcalde, cucha pitera, colaecaiman Siluriformes
Loricariidae
9
0.02
Sternopygus macrurus (Bloch & Schneider 1801)
Caloche
Gymnotiformes
Sternopygidae
4
0.01
Sternopygus aequilabiatus (Humboldt, 1805)
Caloche, yumbila
Gymnotiformes
Sternopygidae
7
0.02
Species
Hypostomus hondae (Regan, 1912)
Vernacular name
Order
Family
0.12
0.07
94
ENSO cycles and potamodromous migrations
Species
Vernacular name
Order
Family
Abundance
(n)
(%)
3
0.01
Sturisoma panamense Eigenmann 1889
Cucha pitera
Siluriformes
Loricariidae
Sturisomatichthys leightoni (Regan, 1912)
Cucha pitera
Siluriformes
Loricariidae
2
0.01
Trachelyopterus insignis (Steindachner, 1878)
Rengue
Siluriformes
Auchenipteridae
1
0.00
Triportheus magdalenae (Steindachner, 1878)
Arenca, tolomba
Characiformes
Triportheidae
6
0.02
Xyliphius magdalenae Eigenmann, 1912
Matacaiman
Siluriformes
Aspredinidae
2
0.01
31983
100.00
Total
95
ENSO cycles and potamodromous migrations
120
120
Capture ratio (%)
February 2008
100
80
80
60
60
40
40
20
20
0
0
0
5
10
15
20
25
0
August 2010
Capture ratio (%)
5
10
15
20
25
120
120
February 2011
100
100
80
80
60
60
40
40
20
20
0
0
0
1
2
3
4
5
6
7
8
0
9 10 11 12 13 14 15 16
120
1
2
3
4
5
6
7
8
9 10 11 12 13 14 15 16
7
8
9 10 11 12 13 14 15 16
1.2
February 2012
August 2011
Capture ratio (%)
Prochilodus magdalenae
Other species
August 2008
100
100
1.0
80
0.8
60
0.6
40
0.4
20
0.2
0
0.0
0
1
2
3
4
5
6
7
8
9 10 11 12 13 14 15 16
0
1
2
3
4
5
6
Sampling days
Figure 19. Daily landing proportion of P. magdalenae and all the others species during the six
assessed migratory seasons in the lower basin of La Miel River. February upstream migrations
are called locally subiendas while august migrations are called mitacas.
It was also notorious that L. muyscorum, S. affinis, P. grosskopfii, Pseudoplatystoma
magdaleniatum and Sorubim cuspicaudus were more important during the first semester
upstream migrations, the subiendas. On the other hand, I. longirostris was more important
96
ENSO cycles and potamodromous migrations
during the second semester upstream migrations, the mitacas. P. blochii and C. mivartii do not
showed a clear pattern but were frequent and abundant in the mitacas, with the maximum catch
value in the 2011 mitaca. It is important to remark that S. affinis and Brycon rubricauda, two
large-size and high value commercial species showed a decreasing trend throughout the studied
period.
60
60
Brycon moorei
February
Brycon rubricauda
Curimata mivartii
Ichthyoelephas longirostris
Leporinus muyscorum
Pimelodus blochii
Pimelodus grosskopfii
Pseudoplatystoma magdaleniatum
Salminus affinis
Sorubim cuspicaudus
Capture ratio (%)
50
40
30
20
2008
40
30
20
10
10
0
0
35
0
5
10
15
20
25
Capture ratio (%)
35
0
5
10
15
20
25
February 2011
August 2010
30
30
25
25
20
20
15
15
10
10
5
5
0
0
0
1
2
3
4
5
6
7
8
0
9 10 11 12 13 14 15 16
35
1
2
3
4
5
6
7
8
9 10 11 12 13 14 15 16
35
August 2011
30
Capture ratio (%)
August 2008
50
February 2012
30
25
25
20
20
15
15
10
10
5
5
0
0
0
1
2
3
4
5
6
7
8
9 10 11 12 13 14 15 16
0
1
2
3
4
5
6
7
8
9 10 11 12 13 14 15 16
Sampling days
Figure 20. Daily landing proportion of the commercial species during the six assessed
migratory seasons in the lower basin of La Miel River.
97
ENSO cycles and potamodromous migrations
The monthly catches in the Manso River showed strong pulsing changes in the abundance of
the most commercial migratory species, which seems to be related to the water level of the
Magdalena River (Figure 21,
98
ENSO cycles and potamodromous migrations
Table 13). The lowest value of CPUE occurred during the 2010-mitaca and the 2008-mitaca,
both after the lowest levels of Magdalena River water level caused by the warm phase of the
Southern Oscillation – El Niño of 2006-2007 and 2009-2010 (Figure 22). In the other hand, the
highest values of CPUE were registered in the first migration of 2011, 2009 and 2008 (in
decreasing order), all these years characterized by high Magdalena River water levels caused by
the cold phases of the Southern Oscillation – La Niña 2007-2009 and 2010-2011 (Figure 22).
The proportion of mature and immature individuals performing the upstream migrations of
Magdalena River Basin changed over the study period, with a greater proportion of mature fish
during 2008-subienda and 2010-mitaca, and a greater proportion of immature fish during 2008mitaca, 2011-subienda and 2011-mitaca (Table 12).
Table 12. Proportion of immature (I) and mature (M) individuals for the four most important
potamodromous species during six upstream migrations in La Miel River Basin.
Species
sub08
mit08
mit10
I
M
I
M
I
Curimata mivartii
17.9
82.1
56.8
43.2
Ichthyoelephas longirostris
42.8
57.2
95.2
4.8
21.4
Leporinus muyscorum
18.9
81.1
92.0
8.0
Prochilodus magdalenae
18.1
81.9
67.5
Total
19.2
80.8
72.2
M
sub11
mit11
I
M
I
0.0
100.0
78.6
66.7
33.3
100.0
61.1
38.9
92.2
7.8
32.5
26.3
73.7
80.0
27.8
27.2
72.8
80.6
M
sub12
I
M
100.0
0.0
0.0
50.0
50.0
65.0
35.0
71.4
28.6
20.0
71.8
28.2
58.0
42.0
19.4
71.6
28.4
58.3
41.7
99
ENSO cycles and potamodromous migrations
1.4
CPUE (ind/throw)
1.2
109.5
1.0
109.0
0.8
108.5
0.6
108.0
0.4
107.5
107.0
0.2
0.0
07
Water level (m)
110.0
All migratory species
Magdalena River water level
Monthly Manso River data set
La Miel Basin upstream migrations data sets
07
08
08
09
106.5
106.0
09
10
10
11
11
12
Year
Prochilodus magdalenae
110.0
1.2
109.5
1.0
109.0
0.8
108.5
0.6
108.0
0.4
107.5
107.0
0.2
0.0
Water level (m)
CPUE (ind/throw)
1.4
Magdalena River water level
Monthly Manso River data set
106.5
La Miel Basin migrations data set
106.0
07
07
08
08
09
09
10
10
11
11
12
Year
CPUE (ind/throw)
0.30
110.0
Magdalena River water level
Monthly Manso River data set
Leporinus muyscorum
109.5
La Miel Basin migrations data set
0.25
109.0
0.20
108.5
0.15
108.0
0.10
107.5
0.05
107.0
0.00
106.5
Water level (m)
0.35
106.0
07
07
08
08
09
09
10
10
11
11
12
Year
0.05
110.0
Ichthyoelephas longirostris
Magdalena River water level
Monthly Manso River data set
109.5
La Miel Basin migrations data set
109.0
108.5
0.03
108.0
0.02
107.5
Water level (m)
CPUE (ind/throw)
0.04
107.0
0.01
106.5
0.00
07
106.0
07
08
08
09
09
10
10
11
11
12
Year
Figure 21. Catch per unit effort in La Miel River Basin for migratory species and middle
Magdalena River water level (at Middle Magdalena Basin: Puerto Berrío Municipality). Note
that upstream migrations of 2008, 2010-mitaca, 2011 and 2012 subienda correspond to
migratory season assessed daily in the six sampling station of La Miel River Basin, while 2009
subienda and mitaca and 2010 subienda corresponds to monthly sampling of Manso station
during the months of the migratory event.
100
ENSO cycles and potamodromous migrations
Figure 22. Precipitation in percentages with respect to multi-year average between January and
December 2010. Well below normal: 0-30%, moderately below normal: 31-60%, slightly below
normal: 61-90 %, normal 91-110%, slightly above normal: 111-140%, rains moderately above
normal: 141-170% well above normal: greater than 170%). Taken from León (2010).
The monthly percentage of catches in biomass, showed that, the timing of migratory season was
different between years. Thus the “subienda” may occur from January to March, but if the
101
ENSO cycles and potamodromous migrations
conditions are appropriate can extent until may (see 2009-subienda and Magdalena water level;
Figure 21), while the “mitaca” may occur from July to October (
102
ENSO cycles and potamodromous migrations
Table 13). The graphical analysis shows that these variations in timing may be related to the
hydrological conditions of the basin i.e. timing of flooding, as well as to the occurrence of the
El Niño and La Niña Southern Oscillation during the studied period.
In general, the analysis of the Manso River experimental fishing showed the same pattern of
abundance and CPUE exhibited by the data of fishing during the upstream migrations: the first
semester of the year exhibited higher catches. The greatest abundances occurs especially from
January to March, corroborating that the magnitude of the subienda is higher than the mitaca (
103
ENSO cycles and potamodromous migrations
Table 13). Depending on the year, the monthly percentage of catches in number of individuals
was between 9.74% and 28.03% during the subiendas, while during the mitacas it was between
5.31% and 11.40%, On the other hand, the values of the percentages of catches in biomass were
between 8.06% and 27.14% during the subiendas and between 4.21% and 11.29% during the
mitacas. These percentages, depending on the year, totalized around 37-51% of the annual
numerical catches for the subienda, around 7-23% for the mitaca, and around 35-67% of the
annual biomass catches for the subienda and between 4 to 24% for the mitaca. Thus, in the study
period in Manso River, both upstream migrations contributed about 62% of the annual catches
(
104
ENSO cycles and potamodromous migrations
Table 13).
105
ENSO cycles and potamodromous migrations
Table 13. Percentage of the monthly numerical catches in the Manso River. Bold numbers were
used to calculate the total catch for each migration; highlighted months correspond to subienda
(first semester of the calendar year) and mitaca (second semester of the calendar year).
Month
January
February
March
April
May
June
July
August
September
October
November
December
Subienda
Mitaca
Total
2009
14.04
13.09
7.97
16.13
8.35
5.69
8.35
5.31
10.06
4.55
6.45
37.76
23.72
61.48
2010
21.32
17.26
13.2
10.15
7.61
6.09
7.11
2.54
2.54
1.02
4.06
7.11
51.78
7.11
58.88
Numerical (%)
2011
9.74
13.54
28.03
5.7
6.41
0.48
6.89
5.46
11.4
0.71
6.65
4.99
41.57
23.75
65.32
2012
40
25
35
-
Total
9.39
15.1
19.67
7.02
10.37
4.73
5.96
5.88
6.61
4.73
4.9
5.63
44.16
18.45
62.61
Individuals were significantly different in size among of the monitored migratory periods
(standard length H(8, N=32727) = 2800.652, p =0.000; χ2=(8, N=32727)= 1937.026, p=0.000 and weight
H(5, N= 32586) = 2846.737, p =0.000; χ 2=(8, N= 32586) = 2361.966, p=0.000). This was also verified
for individuals of the most abundant species: P. magdalenae (standard length H(8, N= 28480) =
2564.341, p =0.000; χ 2=(8, N=
28480)=
1673.848, p=0.000 and weight H(5, N= 28480) =2765.696, p
=0.000; χ 2=(8, N= 28480) =1961.276, p=0.000), L. muyscorum (standard length H(8, N= 1764) =
346.1062, p =0.000; χ 2=(8, N=1764)= 205.4170, p=0.000 and weight H(5, N= 1754) = 389.3696, p
=0.000; χ 2=(8, N= 1754) = 277.7647, p=0.000) and I. longirostris (standard length H(8, N= 796) =
0.0000, p =0.000; χ 2=(8, N= 796)=, p=0.000 and weight H(5, N= 796) =0.000, p =0.000; χ 2=(8, N= 796)
= 133.8958, p=0.000). A similar pattern was observed for Siluriformes species, except P.
bufonius (χ 2=16.06; p<0.04) and C. mivartii (χ2=7.3777; p<0.04). In average the biggest
individuals captured during both migrations of 2008 and 2010, and the smallest during the
second migration of 2009 (2009 mitaca) and first migration of 2011 (2011 subienda). It is also
106
ENSO cycles and potamodromous migrations
noticeable that individuals of 2010 subienda exhibited a wider range of size than the other
assessed migrations (Figure 23).
Figure 23. Differences in standard length and total weight of potamodromous species in La
Miel River Basin during nine upstream migrations. Note that 2008 subienda and mitaca, 2010
mitaca, 2011 subienda and mitaca, and 2012 subienda correspond to migratory season assessed
daily in the six sampling station of La Miel River Basin, while 2009 subienda and mitaca and
2010 subienda corresponds to monthly sampling of Manso station during the months of the
migratory event (Table 12).
Additionally, even when it wasn’t significant, we found positive trend between the CPUE
(r2<0.5; p>0.05) of each migration with the standard deviation of the Magdalena water level
when a time lag of one year was considered. A negative trend between fish size and the standard
deviation of the Magdalena water level was also observed when a time lag of one year was
considered but it wasn´t significant (r2<0.5; p>0.05) (Figure 24, Figure 25, Table 14). There
were no clear relations between any other hydrological variable and the fish migrations or the
fish size without time lag, nor with six-months-time lag (r2<0.2; p>0.05).
107
ENSO cycles and potamodromous migrations
Figure 24. Relations between catch-per-unit-effort, mean total weight and mean standard length
of Magdalena potamodromous fish and the standard deviation of Magdalena water level with a
time lag of one year. Thus, 2008-subienda was plotted with SD value of 2007-subienda and so
on.
migratory season
sub07
mit07
sub08
mit08
sub09
mit09
sub10
mit10
sub11
mit11
sub12
110.0
109.5
109.5
Water level (m)
108.5
108.5
108.0
108.0
107.5
107.5
107.0
107.0
Mean ± SD
Water level
106.5
106.0
Jan07
Mean water level (m)
109.0
109.0
106.5
Jul07
Jan08
Jul 08
Jan09
Jul09
Jan10
Jul10
Jan11
Jul11
Jan12
month
Figure 25. Magdalena River water level and and its standard deviation.
108
ENSO cycles and potamodromous migrations
Table 14. Magdalena River hydrological variables, potamodromous fish size variables and CPUE for each semester: Mean Magdalena
River water level and its standard deviation, minimum and maximum water levels (Mean water level ± SD), number of days under the
minimum level (DUM = number of days<107.36), and over the maximum level (DOM = number days>108.76). Mean multiannual water
level (2002-2012). W = mean total weight (g); L = mean standard length (mm); K = Fulton’s condition factor (K=W/L3, where W = the
weight of the fish, and L is the standard length in centimetres); and the total CPUE (individuals/throw) of each assessed reproductive
period.
Semester
sub07
mit07
sub08
mit08
sub09
mit09
sub10
mit10
sub11
mit11
sub12
2002-2012
Mean
107.85
108.13
108.36
108.45
108.24
107.44
107.48
108.42
108.43
108.14
107.80
108.1
Magdalena River levels
SD
Min.
Max.
DUM
0.85 107.00
108.70
55
7
0.57 107.56
108.71
0.55 107.82
108.91
4
0.63 107.82
109.08
6
0.45 107.79
108.69
3
0.36 107.08
107.79
78
0.80 106.69
108.28
86
0.69 107.73
109.11
10
0.79 107.64
109.21
16
0.85 107.29
108.99
35
0.46 107.34
108.26
23
0.70 107.36
108.76
DOM
32
32
42
51
29
0
9
48
54
46
1
Potadromous fish migrations
W
L
K
CPUE
223.2
241.1
202.8
146.5
281.8
277.7
165.0
181.0
197.9
225.0
236.9
227.7
196.3
254.6
237.2
207.5
211.1
218.8
1.842
1.639
1.675
1.988
1.737
1.935
1.816
1.881
1.835
1.011
0.369
1.183
0.889
0.567
0.277
1.296
0.583
0.658
109
ENSO cycles and potamodromous migrations
DISCUSSION
Timing of migratory events is related to regional rain patterns and the hydrological conditions
of the main basin (Magdalena River Basin), with a high component of variance related with the
El Niño Southern Oscillation, both its cold – La Niña – and its warm – El Niño – phases.
Additionally, even when correlations of abundance and CPUE were not significant, we observed
a trend that could be explained partially by the succession of ENSO events occurred during the
study period: "La Niña" 2007/2009, "El Niño" 2009/2010 and again "La Niña" 2010/2011, this
last La Niña ended around June of 2011. Thus, it occured a transition from La Niña to El Niño
in June 2009, subsequently gave a quick change back to a La Niña event in mid-2010 (León,
2010).
Accordingly, in the Magdalena River Basin from the last half of 2009 until the end of March
2010 due to the El Niño, the dry season was longer and more pronounced than usual
(precipitation well below normal; León, 2010), which was reflected in the lowest levels
registered for the Magdalena river, which were insufficient to split over and flood the floodplain,
affecting in turn the recruitment and the number of migratory spawning-fish. This is reflected
in the size of individuals performing the 2010 migrations, especially the subienda, since due to
the lack of young-of-the-year, the mean standard length and weight of the individuals was the
maximum recorded (minimum catch size of P. magdalenae was 17.5 cm). These fish may
mainly belong to cohorts of 2008 and 2009, which grew under "La Niña" conditions, i.e.
abundance of nursery habitats and food. At the same time also increases food availability and
rapid growth for adults and juveniles as it has been reported (Gomes & Agostinho, 1997,
Agostinho et al., 2004). Thus, "La Niña" had two observed effects during assessed migratory
seasons: greater size and weight of the individuals involved in 2010-mitaca, probably caused by
increased growth of individuals during the first half of 2008; and greater recruitment during the
second half of 2008, first half of 2009 and second half of 2010 observable during 2009-mitaca
and both migrations of 2011, as stated earlier, involving a large number of small juvenile fish
(minimum catch size for P. magdalenae was 10 cm).
A similar phenomenon must be observed during 2009-mitaca, which was dominated by small
young fish. These fish may mainly belong to cohorts of 2008, which grew under "La Niña"
110
ENSO cycles and potamodromous migrations
conditions. Although “La Niña” of 2009 was of short duration, it had a strong impact on patterns
of tropical convection and winds in north of South America: precipitation in Colombia showed
excesses between 40% and 70% during the first quarter of 2009, especially in the Andean region
(León, 2010). These rain excesses, strong flooding and abundant resources cause fish to grow
rapidly and /or a little more than usual, as has been reported for other species of the same genera
in the Parana River in Brazil, which present condition factors and values of visceral-somatic
relationship positively related to high water levels (Gomes & Agostinho, 1997), with higher
recruitment in years of longer duration of floods (Gomes & Agostinho, 1997; Agostinho et al.
2004). Thus, these two phenomena together ("El Niño" and "La Niña") and its impact on
migratory fish stocks, explain migration pattern observed in La Miel River.
As Magdalena River potamodromous fish has two annual possibilities to reproduce, the size
(length and weight) of individuals and the amount of fish performing each migration depend on
a summation of environmental conditions, which affects fish simultaneously in the floodplains
and in the river, at each stage of their life cycle. Prochilodus magdalenae kept in captivity
reaches its sexual maturity at one year of age (Atencio-García, personal communication, June
19, 2015). Under variable environmental conditions, however the sexual maturity can be
delayed if unfavourable conditions persist. Conversely, the fish may be precocious if the
conditions are optimal. Consequently, the prevailing environmental conditions affect the youngof-the-year participation during next migrations. As the migrations are an energy-demanding
behaviour, fish must have minimal reserves to perform the trip and synthetize gonadal tissue.
Thus, for adult fish the prevalent conditions before the migratory periods, while they are feeding
in the floodplain lakes, are crucial, affecting the number and size of migratory fish performing
each migration. Additionally, the environmental conditions during the spawning period affect
the reproductive success and recruitment, affecting the number of migrants during next years.
All these situations highlights a complex pattern due to the bimodal hydrological pattern of the
basin and the reproductive success of at least P. magdalenae (Figure 26).
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ENSO cycles and potamodromous migrations
Figure 26. Schematic summation of environmental and biological conditions that affects the size (length and weight) of individuals and
the abundance of potamodromous fish performing each migration in the Magdalena Basin.
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ENSO cycles and potamodromous migrations
Fisheries in La Miel River are sustained by potamodromous species that arrive twice a year from
the Middle and Lower Magdalena Basin, being the bocachico, Prochilodus magdalenae the main
resource. A similar pattern can be observed in other rivers of northern South America, where most
commercially important taxa are large fish that become especially vulnerable during long annual
migrations in the river channel (Lewis et al. 2006). In South American basins in which genera
Prochilodus is distributed its species are always economically important (Castro & Vari 2003,
Larinier 2001). For example, it has been estimated that in Amazon and Orinoco basins two
genera, Colossoma and Prochilodus probably constitute more than 50% of the total catch (Lewis
et al. 2006), and approximately ten of the most important species account for about 93% of the
catch in the Amazon (Junk, 1984). In Colombian rivers historically Prochilodus magdalenae
has been the mainstay of fisheries (Valderrama et al., 2011) and it has been considered as the
most economically important species in Colombian rivers (Ortega-Lara et al., 2000), fact that is
supported by our results.
All large rivers of northern South America show marked seasonality in the hydrograph, most of
them show a unimodal seasonal discharge pattern, but the Magdalena has a more complex
pattern including dual minima (Lewis et al. 2006) (February, August). Related with the low
water levels, potamodromous fish leave the lakes in the floodplain to start an up stream
spawning migration, with spawning of the fish fauna typically occurring one per year on the
rising limb of the hydrograph (Lewis et al. 2006). Synchronization of spawning of migratory
species with periods of rain, when water levels rise, is frequently mentioned in the literature
(Lowe-McConnell, 1987, Vazoler, 1996, Agostinho et al., 2007), for example Godoy (1975)
reports that during the reproductive season Prochilodus spawns every time the rains cause an
increment in water level. Thus, in monomodal rivers, fish migrate once a year independently of
the geographical variation in the timing (months of the year). Thus Prochilodus magdalenae in
the middle Atrato undergoes subienda from December to April and spawning between April and
May (Jaramillo-Villa and Jiménez-Segura 2008); in the Sinú River spawning season occurs
between March and September, with a reproductive peak in May and June (Olaya-Nieto et al.,
2003); in the Andean piedmont of western Venezuela “Ribazons” of Prochilodus mariae occurs
from mid-November until March (Duque et al., 1998). Subtropical rivers also exhibit a similar
pattern, for example in the Upper Paraná Basin migration and spawning occur between October
and March (Carolsfeld 2003). In the Magdalena River Basin, with its dual minima, at least one
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ENSO cycles and potamodromous migrations
fraction of the P. magdalenae and probably L. muyscorum populations (see chapter 2), migrate
and spawn twice a year.
Prochilodus magdalenae has a special feature that allows that at least the individuals of this species
with enough energetic reserves migrate twice per year, and due to its abundance, modulate in this
way the magnitude of the Magdalena fish migrations. Due to its asynchronous development of the
gonadal tissue in two groups, P. magdalenae in captivity can be induced hormonally to
reproduction twice a year. Thus, after ovulation and spawning require approximately three
months to reach final maturation and be suitable for a new hormonal induction, without effect
in their ovulation rates, but the absolute and relative fertility can be reduced between 24% and
66% and fertilization and hatching rates between 23% and 36% (Atencio et al., 2013).
Consequently, if the species could be induced twice a year in captivity, under natural conditions
and under appropriate stimuli, it is also physiologically able to reproduce naturally twice a year,
as has been suggested by mark-recapture experiments in the basin (see Chapter 2), and
ichthyoplankton densities drifting in the Magdalena River (Jiménez-Segura, 2010). Thus, we
believe that additional to the component of the variance explained by the inter-annual
fluctuations in magnitude and duration of flooding, the difference in magnitude between the
migrations of the same year, i.e. subiendas and mitacas, can be explained by the reported
decrease in fertility, fertilization and hatching rates of individuals that perform the two annual
migrations.
The two migrations of 2011 were characterized by their magnitude in relation to the numerical
abundance, with a large number of sub-adults and immature individuals, of small size and low
weight, as also occurred in 2009 migrations. This difference is even noticeable when the three
subiendas (2008, 2011 and 2012) are compared, as well as the three assessed mitacas (2008,
2010 and 2011), with catches during the migrations of 2011 that doubled the catches of 2008mitaca and 2010 and 2012 subiendas. On the other hand, the size of the individuals involved in
migration was larger in both 2008 migrations, 2009-subienda and 2010-subienda and mitaca,
registering the largest records of maximum, minimum and average sizes during these periods,
and being lower during migrations of 2011. Additionally, it is important to mention that although
the magnitude of the subienda in 2011 (in number of individuals) many of these individuals
weren’t caught by fishing gear because they were so small that escaped from cast nets.
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ENSO cycles and potamodromous migrations
According to the fishermen: "it is been long since we last saw". Thus, strong “Niñas” may
produce big number of small fish (high recruitment) while strong “Niños” may produce low
number of big fish (without young of the year) as has also been reported for Sogamoso River
(ISAGEN S.A., unpublished data), and upper Magdalena River (Garay, 2016). Low water levels
persisting for relatively long periods may result in the complete absence of young of the year
(Welcome, 1979). By contrast, the high waters during the periods after migration (postspawning) favour the recruitment and survival of juveniles, as they provide nursery habitat for
longer periods, causing fast growth, thus reaching larger sizes and consequently have less
aquatic and terrestrial predators, moreover the absence of the stress associated with dry periods
should also promote survival (Agostinho et al., 2004). Additionally, duration and magnitude of
flooding in rivers with floodplains are positively related to the number of spawning individuals
(Agostinho et al., 2004).
It has been reported that fish that have early stages of their life cycle, either eggs or larvae
drifting downstream of the basin, must eventually return in an upward migration upstream as
juveniles or adults to meet parental adults (Baras & Lucas, 2002). This migration of juveniles is
a recognized phenomenon for other species of Prochilodontids (P. argenteus in the São
Francisco River and P. lineatus in the Mogi Guaçu River) and is known locally as "arribação"
(Godinho & Kynard, 2006). A similar phenomenon should occur in the Magdalena Basin, a fact
that would explain the size and state of maturity of the individuals which made the 2009-mitaca
and the migrations of 2011, presenting a greater proportion of immature individuals than mature
or maturing, contrary to what was found in 2010-mitaca.
Changes in abundance of the other commercial migratory species must be related to the
differential effects of flow fluctuations. Reproductive success, recruitment, growth rates,
between others, in each species could change in response to flow fluctuations (LoweMcConnell,
2003), in this way, the successive drought phenomena (El Niño phenomenon) and flooding (la
Niña phenomenon) observed in the basin during the study period, which has much stronger
effects on migratory species (Agostinho et al., 2004). For example, rivers, particularly those
with highly variable annual hydrographs, appear to have separate components that are adjusted
to years of high flow and years of low flow. In years when the floodplains flood normally, the
high flow elements predominate, and in years when the floodplains do not flood, the low flow
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ENSO cycles and potamodromous migrations
elements are more abundant. This variability may arise from separate species that are adapted
to low flow and high flow (LoweMcConnell, 2003).
The daily variation in catches was higher in subiendas than in the mitacas. We believe this may
be because mitacas are smaller (in numerical abundance), therefore, during these migrations fish
should be more grouped, forming close schools, generating less dispersion in catches. By
contrast, during the subienda, fish are distributed in several groups (called "puntas" by
fishermen) and depending on their movements and swimming advance throughout the river and
its tributaries, generating differences more dispersion in catches.
Understanding the effects of ENSO cycles is very important, especially when climatic change
scenarios are taken in mind. For Colombia, the IDEAM forecast an increase in the frequency of
occurrence of such events and in its magnitude. In other words, it is expected that during next
years we will see more of these ENSO cycles and each time being more extreme: longer and
stronger droughts and floods. This phenomenon could have serious impacts in potamodromous
fish populations and its based fisheries.
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Considerations and implications for fisheries
CHAPTER 6: GENERAL CONSIDERATIONS AND IMPLICATIONS FOR
FISHERIES MANAGEMENT
Historically, potamodromous fish and their cyclical movements have played a key role in the
Magdalena Basin and its inhabitants, not just as an economic activity or as a temporal food
source for many families, but as part of the life of riverine populations’ life, culture and folklore.
Thus, each year is common to see on the television and newspapers’ news some allusions to the
subienda of Magdalena River potamodromous fish and the high temporal fish abundance in
Magdalena ports. This is true in such level that a simple search in Google Colombia for
“subienda”, “subienda pescado” and “subienda río Magdalena”, shows near 90000 results
(71300, 10300 and 4870, respectively). On the other hand, the same search in Scholar Google
(https://scholar.google.com.co/) shows about 850 results (419, 201 and 256 respectively), most
of them are mentions of technical reports of National Environmental Agencies. This trend
demonstrate that despite the importance of Magdalena migrations for Colombian population,
the scientific knowledge about potamodromous fish is scarce, and mostly concentrated in grey
literature.
One of the most important contribution of this research is to describe, based in experimental
data, the migratory pattern of the most important freshwater fish of our country, putting real
numbers to the knowledge that fishermen and Colombian ichthyologist had passed down for
generations, reinforcing some popular beliefs and contributing with some totally new data and
knowledge. This is how the results of this project indicate that in the Magdalena Basin there are
at least 13 potamodromous species, three more species than stated in the national reports (Usma
et al, 2009; Lasso et al., 2011; Zapata & Usma, 2013), being necessary the inclusion of at least
Brycon rubricauda, Cynopotamus magdalenae and Ichthyoelephas longirostris. Additionally, it
is necessary to classify bocachico, Prochilodus magdalenae, as a long-distance migratory
species and moíno, Leporinus muyscorum, as a middle-distance migratory species.
Though the statement above may sound bombastic, it has serious implications for conservation
and management purposes. Knowledge of the use of space over time in fish is crucial to
understand population processes and communities (Lucas & Baras, 2000). For instance, the
inclusion of this three new species as migratory implies that any conservation measure for this
117
Considerations and implications for fisheries
species need to take into account long or median cyclical movements, which in any case,
expands its home range, so fish on the floodplain and on the Magdalena River tributaries, may
be considered as a single fish population and not as separate populations. Consequently, the
change in the classification of the migratory condition of P. magdalenae and L. muyscorum may
change the area of influence of conservation measures and resources allocations. This is also
true for the finding of P. magdalenae performing movements beyond HydroItuango location.
This necessarily means that an important migration route is being disrupted.
We now know that potamodromous fish that spawn in the Middle Magdalena tributaries make
movements ranging between 68.8 and 203 km from the mouth of La Miel River, and that during
the migratory season, fish swim actively searching for the best environmental conditions,
avoiding what could be considered as unfavourable habitat conditions in their search for
spawning grounds. Although we still don’t know if during the bajanza, the downstream
migration to the floodplains, the entrance to feeding and growing grounds is random or occurs
with certain homing degree, thus further studies with radio tags or otoliths chemistry analyses
are now necessary.
The finding of at least one potamodromous fish species able to perform consecutively both
annual upstream migrations refutes the hypothesis of the presence of two populations
reproducing separately in the same river, which would imply the presence of at least two
different subpopulations for potamodromous species in the basin. At the same time, these results
support the rising of a new hypothesis to explain the two upstream migrations: Magdalena
upstream migrations are performed by the same population but just one fraction is able to
perform both, subienda and mitaca, consecutively, due to the energetic costs of this display,
maintaining “migrant” and “non-migrant” individuals in a transitory state (fish will eventually
belong to any of these categories in accordance with their energy reserve). So, even when first
semester migrations is always bigger (the subienda), special efforts should be directed to protect
both migrations, especially the second semester migration (the mitaca). Taking in mind the fact
that fish that performs the second migration may have higher fitness, protection measures should
be considered, because its conservation would play a key role in the maintenance of Magdalena
Basin potamodromous fish populations. Additionally, further studies would be necessary to find
out whether the other potamodromous species adjust to the same hypothesis or not, as well as
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Considerations and implications for fisheries
further research on the determination of the proportion of P. magdalenae individuals that are biannual migrants would help to clarify and understand the population dynamics of this species
and the migrations dynamics by themselves.
As mentioned in the third and fourth chapter potamodromous migrations in Magdalena Basin
respond to both small scale and regional changes in water levels. In small scale, potamodromous
migrations movements and its fisheries respond to small variations. Such as the ones related to
Miel I hydropower plant flow regime due to energy generation, and peculiarities of each river
basin stretch, causing daily variations in fish abundances and densities inside the basin. Even
when these results are specific for La Miel River Basin, is expected that similar behaviour could
be displayed in other regulated Andean Magdalena Basin rivers, therefore, deserve further
analysis, especially if considering that dam design features, the river, and its fish fauna make
impossible the generalizations about possible effects in fish habitat requirements and fisheries.
Reinforcing how wrong is the assumption that regulated rivers exist as a continuous gradient of
physical habitat, and that species will respond in a predictable and continuous manner, that is
still commonly overlooked in some studies (Murchie et al., 2008). All this new knowledge is
essential for decision makers and river managers, as well as energy producers, to the
improvement of river management practices, especially if a balance is to be met between
supporting the economic interests of humans – energy producers and riverine livelihoods – and
the ecological requirements of fish. For instance, this could be the basis for policies of generation
levels that simulate adequate conditions for both, human and fish.
Moreover, regional changes in rain patterns related to ENSO cycles, affect the Magdalena Basin
water levels, which in turns causes inter-seasonal and inter-annual fluctuations in abundance
and reproductive success of potamodromous fish, thus affecting fisheries and fish populations
survival. As was stated before, El Niño - warm phases of ENSO cycles, promote recruitment
failure and affects length and weight gains, as well as the number of individuals performing the
upstream migration. On the other hand, La Niña-cold phases of ENSO cycles, may promote
increased recruitment, rapid and more gains in length and weight, as well as an increased number
of fish performing upstream migrations. The understanding of these effects in potamodromous
fish populations could have serious implications for conservation and management of this
species.
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Considerations and implications for fisheries
An illustration of this appears clear when the new scenarios of climatic change are taken in
mind. This year, the IDEAM, the National Institute of Environmental Studies, published its
predictions for weather 2011-2100 as a scientific tool for decision-making (IDEAM, 2015),
which forecast an increase in the frequency of occurrence of such events and in their magnitude.
In other words, it is expected that during the next years we will see more of these ENSO cycles
and each time being more extreme: longer and stronger droughts and floods.
In potamodromous fish species, spawning is coordinated in time and space with conditions that
favour the survival of offspring during early life history stages, but stochastic fluctuations in
these conditions may generate variations in reproductive success among individuals, as well as
causing variations in population size (Dodson, 1997).
This could be crucial if we think about a series of continuous El Niño occurring in synergies
with overexploitation of fish stock. In that case, the new scenarios pointed by the IDEAM, could
cause a collapse in potamodromous Magdalena Basin fisheries and fish populations as it was
documented in the collapse of the sábalo (Prochilodus lineatus) fishery, in the Pilcomayo River
in Bolivia. These phenomenon can be attributed to the 1990–1995 El Niño event and subsequent
overexploitation of the fish stocks (Smolders et al., 1999).
On the other hand, knowing that La Niña promotes recruitment, it could be used as a tool for the
recovery of potamodromous fish populations. During La Niña years, big amounts of small
juvenile fish are caught. Those fish have very little economic value, but fishermen are tempted
by the temporal abundance of fish. If this non-friendly practice could be avoided, via fishermen
education, massive campaigns or in the worst of cases via official regulations to punish this
practices, it would have a very positive impact in the size of Magdalena fish populations, with
better yields and economic benefits to fishermen in the medium and long term.
Current pressures on water from humans, means that there is an increasing trend to control
hydrological regimes. Such interventions almost inevitably act to the detriment of living aquatic
resources and fisheries. Losses of fish catch below dams and other river regulating structures
are now known to be significant and represent a considerable loss of food and income to the
societies exploiting them (World Commission on Dams 2000). Due to the dependence of a
significant amount of families on potamodromous fish as a protein source in the Magdalena
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Considerations and implications for fisheries
Basin, as well as an economic income, the new knowledge here produced could have enormous
environmental and socio-economic implications for Colombian society and decision makers.
121
References
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