1
CM 2002/O: 10
INFLUENCE OF INTERANNUAL VARIABILITY OF HYDROGRAPHIC
PARAMETERS SPATIAL DISTRIBUTION IN THERMOCLINE AND
HALOCLINE ON SPRAT EGGS AND LARVAE DISTRIBUTION AND
SUBSEQUENT JUVENILES ABUNDANCE IN THE SOUTH - EASTERN
BALTIC SEA
E. Karasiova
Atlantic Scientific Research Institute of Marine Fisheries and Oceanography (AtlantNIRO),
5, Dm.Donskoy Str., Kaliningrad, 236000, Russia
Tel.: 007 0112 225 265, Fax: 007 0112 219997, E-mail: [email protected]
ABSTRACT
During 1990s as a result of the global warming cold winters in view of their
rarity were not any more the principle abiotic factor determining the Baltic sprat
abundance. Based on the assumption that hydrographic processes causing the
environment heterogeneity can be important to juvenile sprat survival, the spatial
variability of hydrographic parameters (temperature, salinity, density, oxygen)
distribution in the halocline and thermocline of the south-eastern Baltic in April-May
1993 and May-July 1998 (poor year-classes) and in May 1994-July 1999 (strong yearclasses) was studied in the framework of STORE project. The most evident
differences in the Gdansk Deep for the years considered are prevailing trend to
increase of salinity and temperature and decrease of oxygen in the halocline at the
depth of 70 m in off-shore direction (mostly from the east to the west or from the
south-east to the north-west) in 1993 and 1998; the opposite trend to increase of
salinity and temperature and decrease of oxygen in the halocline towards the coast
was observed in 1994 and 1999. The thermocline was located at the depth of 40 m
(below the photic zone) in July 1998 in the eastern part of the Deep as compared to 20
m in July 1999 (within the photic zone). It is assumed that one of causes of those
differences seems to be a variant location of water upwelling and downwelling zones.
The distribution of sprat eggs and larvae relatively to their coincidence or noncoincidence with the above said zones in view of probable impact upon sprat larvae
survival is considered.
INTRODUCTION
Long-term researches of the Baltic sprat abundance dynamics revealed that
this species recruitment is subjected to significant inter-annual variability. It is
assumed that the principle factors determining sprat year-classes strength are the
water temperature and inter-species interactions of sprat and Baltic cod (Koester et al,
2000 ). However, a sharp reduction of cod stock and rarity of cold winters during the
last decade (the only cold winter during 1988-2001 was in 1996) considerable
decreased these factors importance for sprat recruitment formation. It can be assumed
that at present the role of hydrographic processes increased resulting in nutrients
transport into the adult sprat feeding areas and providing formation of gradient zones
promoting young sprat food items concentration. In the Baltic Sea with a unique
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hydrographic structure the boundary layers –halocline and thermocline - are very
important for hydrodynamic and hydrochemical processes formation. Researches of
spatial variability of hydrographic parameters distribution at the halocline and
thermocline depth levels and its impact upon sprat eggs and larvae distribution will
probably allow to approach the understanding of some mechanisms important to
young sprat survival in the current hydrographic conditions.
MATERIAL AND METHODS
In this work the hydrographic data on temperature, salinity, and oxygen
content obtained during scientific-research cruises of AtlantNIRO (the late Aprilearly May 1993; the late May 1994, the early May 1993, July 1999) and in cruises of
German R/V “Alkor” (the late May and the early July 1998 and 1999) in the SouthEastern Baltic Sea. The data on sprat eggs and larvae abundance (sp./m2) were
obtained from the same sources. The vertically operating ichthyoplankton net IKS-80
was used.
To describe the spatial variability of hydrographic parameters the maps of
temperatures distribution at the depth levels 20, 40 and 70 m, water salinity and
density ( also oxygen content in 1998 and 1999) at the depth levels 70 m, as well as
the plots of water temperature, salinity and density distribution at transects across the
Gdansk Deep were prepared. For the north-western (55º22’N –55º00’N and 19º00’19º10’E) and south-eastern (55º05’-54º47’N and 19º23’-19º35’E) parts of the Gdansk
Deep the depth of the 8 psu isohaline and the lower 4°C isotherm locations were
estimated. The areas with high salinity and temperature values at the depth level 70 m
were interpreted as zones of the halocline and the lower boundary of the cold layer
ascending, while the areas with low salinity and temperature at 70 m were interpreted
as zones of the halocline and the cold layer lower boundary descending. Sprat eggs
and larvae distribution was mapped and compared to distribution of hydrographic
parameters at 70 m depth level.
The data on the Baltic sprat recruitment abundance for 1993, 1994, 1998 and
1999 were obtained from the Report of the Baltic Fisheries Assessment WG 2001.
RESULTS
Mapping of hydrographic parameters horizontal distribution at the depths of
the thermocline and the halocline location revealed significant inter-annual difference
of their variability extent, as well as an availability of two basic distribution patterns
(Fig. 1-5, 7-9, 11, 12).
The most distinguished feature of the first distribution pattern observed in
1994 and 1999 was salinity increase in the upper halocline (70 m) in the southeastern, eastern and north-eastern direction from the area located on the northern
slope of the Gdansk Deep ( 55°10’ - 55°26’N, 19°08’ - 19°24’E in May 1994 and
55°22,5’N, 19°04’ - 19°30’E in May 1999), i.e. towards a near-shore shallow zone
adjacent to the Gdansk Deep from the south-east and the east and to the southern
Gotland Deep from the east. Water temperature and its density at 70 m depth level
revealed the similar pattern of spatial distribution. Water temperature horizontal
distribution in the thermocline layer (20 m) in the late May 1994 was characterized by
the opposite trend of water T° increasing from the shallow zone with the depths of
40-60 m towards the deep-water part of the sea (Fig. 2 A). This trend avoided only a
small area with the depths of 20-25 m off the Curonian Spit. The water temperature at
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20 m depth level varied in the range of 3.17º-8.89ºC. Significant horizontal gradients
observed between isotherms 5-6ºC seem to evidence the temperature front at the
depths from 15 to 25 m in the area of mass sprat reproduction.
Two surveys in May 1999 revealed the similar trend of water salinity
variations at 70 m depth level with the minimum salinity localization on the northern
slope of the Gdansk Deep. However, the trend of the water temperature reduction
was considerably less pronounced at 20 m depth level from the central Gdansk area
towards its periphery as compared to 1994.
Vertical distribution of hydrographic parameters at cross transects in the
Gdansk Deep evidences the decrease of halocline depths from the north-west to the
south-east in May 1994 (Fig.11, 2b). In the deep water part of the Gdansk Deep
(depths from 88 to 103 m) between 55º 10’N – 19º09’E and 54º46.5’N-19º34.3’E the
depth of 8 psu isohaline decreased from 68.1 m to 57.3 m and 11 psu isohaline depth
– from 78.5 to 63.9 m. The similar pattern of water density vertical distribution was
observed at the transect considered (Fig.11,2c). The lower boundary of the cold
intermediate layer (the lower isotherm 4ºC) ascended from 73.0 m to 61.7 m, while its
upper boundary (the upper isotherm 4ºC) – from 26.7 to 18.9 m. In May 1994 the cold
water of the intermediate layer intruded into the coastal shallow zone at the depths
less than 40 m. The depth of the upper isotherm 3ºC location in the shallow zone can
be less than in the deep-water part in 11.8 m (28.7 and 40.5 m, respectively) (Fig. 11,
2a).
The minimum temperature of the intermediate layer in the late May 1994 was
2.43ºC. The most cold water intrusion into the coastal zone was observed in the
Gdansk Deep, where the water temperature below 3ºC was recorded at the bottom at
the depths of 19-20 m, and the water temperature below 4ºC- at the depths of 14 -15
m. In the southern Gotland Deep the water of the intermediate layer with the
temperature below 3ºC penetrated up to the depth of 30 m, and the water with the
temperature below 4ºC – up to 19-18 m. In the northern Gotland Deep the coldest
water with the temperature below 3ºC was not recorded in the coastal zone, while 4ºC
isotherm was located at 21-24 m. In May 1994 the thermocline ascending from the
open-sea station in the north-western part of the Gdansk Deep towards the coastal
station in the south-eastern part (Fig. 11, 2a). This can be traced on the basis of 7ºC
isotherm location change from 20.3 m at the station mostly remote from the eastern
coast to 8.5 m at the near-coast station. Similarity of hydrographic conditions in the
early May 1999 and May 1994 consists in the same reduction of the halocline and
pycnocline depth location from the west to the east, which can be traced in vertical
profiles of these parameters (Fig. 12). The differences includes the initial isotherms
4.5-3.5ºC descending over the depths more than 80 m and further ascending in the
shallow zone. The thermocline was pronounced only in the western part of the Deep
and in the coastal shallow zone. In the eastern part of the Deep the ascending of 5ºC
isotherm, 7psu isohaline and 5.5 isopycnic was observed, probably evidencing that
the upper 20-m layer was covered with upwelling, which resulted in the thermocline
weakening. In the late May 1999 isohalines ascending in the halocline layer was not
pronounced, while 3–5ºC isotherms ascending was significantly more evident in the
cold intermediate layer and the lower thermocline part. In the early July 1999
considerable decrease of isohalines and isopycnics depths was observed in the upper
halocline and pycnocline in the eastern part of the Deep (Fig. 11, 3a, b, c). The
thermocline was located at the depths of 20-25 m and deepened from the north - west
to the south - east.
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The minimum temperature of the cold intermediate layer in the deep-water
areas of the Gdansk Deep was 2.65ºC, 2.72ºC and 2.88ºC in the early May, late May
and early July 1999, respectively. The water of 4ºC intruded into the coastal zone up
to 25-32 m depths in the early May, and up to 36-49 m in the early July.
The different hydrographic situation seems to occur in 1993 and 1998. During
these years an area with the maximum salinity at 70 m depth level was located on the
north-western slope of the Gdansk Deep (Fig. 1 C), instead of the south-east slope, as
in 1994. The temperature spatial variability at the depth levels of 20 and 70 m did not
reveal any distinguished trend (Fig. 1A, 1B). The vertical profiles at the cross
transects of the Gdansk Deep showed discending of 3.5ºC isotherm and 7.5 psu
isohaline located in the cold intermediate layer in direction from the west to the east
(Fig. 10 a, b, c). In the early May the minimum temperature of the intermediate layer
in the Gdansk Deep approached 3.17ºC. The cold water of 4ºC intruded into the
coastal zone eastwards of the Gdansk Deep up to the depths of 8-15 m.
In the late May the maximum salinity at 70 m depth level (10.06 psu) was also
observed in the western area of the Deep (55º10.43’N, 18º49.02’E). A zone of low
salinity and water temperature at this depth level was located in the south-eastern part
of this area. The range of water temperature fluctuations at 20 m depth level was 7.729.47ºC with maximum at the southern eastern periphery.
The spatial distribution of hydrographic parameters in July also revealed
increase of water salinity, density and temperature in the upper part of the halocline in
the western Gdansk Deep. In general, the entire south-eastern and eastern periphery of
the Gdansk Deep, as well as the eastern periphery of the Gotland Deep represented a
zone of the halocline descending which evidence the lower salinity values at 70 m
depth level (Fig. 5.1). The spatial distribution of oxygen content at 70 m depth level
was inverse related to salinity distribution, increasing with the latter reduction and
vice versa (Fig. 5D). Spatial distribution of temperature at 20 m depth level was
characterized by increase from the north to the south, apparently owing to the
latitudinal differences of water heating extent (Fig. 5A). In July 1998 the thermocline
in the southern Gdansk Deep descended significantly to the depths of 40-50 m and
maximum horizontal gradients of temperature were observed in this zone (Fig. 11,
4a). Isotherm 8ºC located in the maximum vertical gradients zone, deepened from the
north to the south (between 55º37’N, 19º 10’E and 54º49’N, 19º25’E) to about 22 m
(from 31.0 to 52.8 m). The minimum temperature of the cold intermediate layer
amounted 3.62ºC and 3.52ºC in the late May and late July 1998, respectively.
The vertical profiles of hydrographic parameters in the Gdansk Deep during
the above mentioned period showed the higher position of the halocline and
pycnocline in the western part as compared to the eastern one. However, variability
of isohalines and isopycnics location eastwards of 19ºE was insignificant.
In May 1998 the thermocline was located at the depth of 22-28 m in the
western Deep and at 25-35 m in the eastern part. The maximum vertical gradients
were observed approximately at 25 m. In July 1998 the thermocline was located at the
depth of 30-50 m in the western part and at 22-52 m in the eastern with the maximum
vertical gradients at 40-45 m. However, the upper boundary of the thermocline (13ºC
isotherm) ascended from the west to the east (from 30.1 m to 23.4 m), as well as 5.0
isopycnic (Fig. 11, 4a,c).
In Table 1 the data on 8 psu isohaline and upper and lower 4ºC isotherms
locations representing the upper halocline and cold intermediate layer position in the
western and eastern Gdansk Deep are shown. The maximum difference between these
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parameters was observed in 1994 and 1999, especially for the lower 4ºC isotherm (up
to 12 m in the early May 1999). All data on this isotherm and 8psu isohaline depth
locations evidence their ascending in the eastern part as compared to the western. The
ascending of the upper 4ºC isotherm was recorded in the late May 1994 and 1999,
while in the early May and July 1999 it descended slightly.
Significantly lower variability of these parameters location was observed in
1993 and 1998. In general it was characterized by insignificant descending of 8psu
isohaline and lower 4ºC isotherm (up to 4 m in 1993) from the west to the east, while
the upper 4ºC isotherm position did not actually differ in the western and eastern
parts.
On Figures 3c, d and 10 the sprat eggs and larvae distribution in 1994 and
1999 was shown. In general maximum abundance of sprat eggs and larvae in the
Gdansk Deep during May 1994 approximately coincided with isohalines 8.5-9.5psu
and thus also with a zone of the highest horizontal salinity gradients at 70 m depth
level.
The spatial location of these areas principally corresponded to zones of low
and medium position of the halocline. Sprat eggs and larvae were absent or were few
at the eastern periphery of the Gdansk Deep within a zone of isohalines 10.0 and
10.5psu horizontal location at 70 m corresponding to the areas of the halocline
ascending. The core with a high abundance of sprat larvae also corresponded to the
area where isotherms 4-7ºC were located at the depths of 20 m forming a zone of high
horizontal and vertical temperature gradients. No larvae were found in the area of
water of below 4ºC ascending to 20 m depth level located in the shallow zone outside
sprat spawning ground.
In 1999 sprat egg abundance significantly exceeded the value in 1994, at the
same time larvae abundance was significantly lower than in 1994 (Table 2). In the
early May 1999 sprat eggs and larvae concentrated mainly in the south-western and
(to the less extent) in the north-western parts of the Gdansk Deep in the areas of
isohalines 8.5-9.0psu and isoxygene 2-3 ml/l location. Eggs and larvae abundance
was low both in the centre of the Deep with the deepening halocline (salinity of
7.5psu at 70 m) and the lower boundary of the cold layer (temperature 3.0ºC at 70 m)
and high oxygen content, and at the eastern periphery of the Deep, where the
halocline ascending (salinity of 9.5 at 70 m) and oxygen content reduction were
observed. In the late May 1999 the highest sprat eggs concentrations were located in
the western Gdansk Deep within the area of isohalines 8.5-9.5 and isotherms 3.54.5ºC location, while sprat larvae concentrated in the southern part within the area of
isohalines 8.0-9.0 and isotherms 3.5-4.0ºC location. In general these areas
corresponded to the average position of the halocline and the cold layer lower
boundary. Relatively low abundance of eggs and larvae (sometimes even the absence
of larvae) were noted both at the western edge of the Deep (ascending of halocline,
salinity above 9.5 at 70 m) and in the centre of the Deep (halocline descending,
salinity below 8.0 psu and temperature below 3.5ºC at 70 m). Larvae concentrations
in the south of the Deep associated with relatively high position of the halocline. In
the early July 1999 the main eggs concentrations were found in the south-western part
of the Deep within isohalines 8.0-8.5psu, isotherms 3.5-4.0ºC and isoxygenes 3.5-4.0
ml/l location zones. Eggs abundance decreased both in the south-eastern part within
halocline ascending zone and oxygen content reduction, and in the north-eastern part
within the halocline descending zone (salinity reduction and oxygen content
increase). Sprat larvae abundance was low with maximum in the south-western and
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south-eastern parts of the survey and approximately corresponded to the zone of
average (the south-west, salinity 8.0-8.8psu at 70 m) and high ( the south-east, salinity
above 9.0psu) halocline position.
In the late April- early May 1993 the highest concentration of sprat eggs and
larvae in general coincided with the areas, where isohalines 8.5-9.5 psu were located
at the depth of 70 m, i.e. between the halocline ascending zone at the north-western
slope of the Gdansk Deep and a descending zone in the south-east. In May 1998 eggs
concentrations were located approximately. within the zone of high and average
halocline location (corresponding to salinity 9.5-8.5psu at 70 m) in the south-western
part of the Deep, while larvae aggregations were found in the zone of the halocline
average position (9.0-8.5psu). In July 1998 the highest eggs concentrations in the area
distributed mostly in the zone of the highest horizontal salinity gradients and
temperature at 70 m between isohalines with the maximum (over 9.5psu) and
minimum (below 8.0psu) salinity. In general larvae aggregations were located more
southwards, associating with areas of high horizontal salinity gradients between
isohalines 8.5-8.0psu and to the zone of maximum thermocline descending (20 m
deeper as compared to the northern Deep, i.e. at 45-50 m layer). Therefore, in most
cases both in successful for sprat recruitment years 1994 and 1999, and in
unsuccessful years 1993 and 1998, sprat eggs and larvae distribution in the Gdansk
Deep associated with the areas of the highest horizontal gradients of salinity and
temperature at the depth of 70 m, which were located between zones of the halocline
ascending and descending (Fig.13-15). In May 1994 sprat eggs and larvae
aggregations were also found in the southern part of the temperature front zone,
observed at the depth level 20 m.
Principle differences between environment conditions at sprat spawning
grounds during successful and unsuccessful years consisted in different locations of
halocline ascending and descending areas, various extent of development of
horizontal gradient zones (more pronounced in productive years 1994 and 1998),
availability of upwelling indications (1994, 1999) or their absence (1993 and 1998),
availability (1999) or absence of water intrusion from the cold layer into the coastal
zone in summer, the thermocline location within the photic zone (1999) or its
descending below the photic zone up to the depth of 45-50 m (1998).
DISCUSSION
The basic reproduction of the Baltic sprat occurred in the deep-water deeps of
the open sea close to halocline layer ( STORE, 2000) during an entire spawning
season though in summer sprat eggs may be found in the coastal zone over the depths
of 50-30 m . The area of the maximum sprat fry aggregations in the early autumn is
the shallow coastal zone with the depths of 20-60 m, though the entire area of their
distribution covers the depths from 100 to 20 m (Ustinova, Shvetsov, 1986). Since
sprat distribution are includes both open and shallow zones of the sea, the processes
related them by means of hydrodynamic, hydrochemical and biological interactions
seem to be considered as the factors affecting sprat year classes abundance. These
should primarily include wind-induced Ekman’s transport, which below Ekman’s
layer is compensated by return flows (Hinrichsen et al., 2001). From the time of
Humbolt’s observations of cold water upwelling in the Gdansk Deep in summer 1834
(Kortum, Lehmann, 1997) upwellings were often recorded in the coastal zone of the
Baltic Sea as a result of in situ observations (Raid, 1989) or satellite data processing
(Bychkova, Victorov, 1987). There are often considered as local events related to the
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bottom topography and coasts outline (Gidhagen, 1984; Raid, 1989). However, on the
basis of the researches carried out under STORE Baltic Project, upwelling is
identified as the key process potentially affecting the recruitment success through fish
larvae feeding conditions (variability of plankton production and aggregations)
(STORE, 2000). Along the eastern coast of the Baltic Sea, as it is shown in this report
for May 1994, the cold water raising to the thermocline layer may cover a vast area
between 54º30’N and 58º N. Probably depending on upwelling intensity and stage, it
is not always fixed directly at the sea surface. Upwelling and its consequences may
appear in the form of the weakened thermocline (the early May 1999) or water
intrusion from the intermediate cold layer into the coastal zone. The latter event
seems to be related to the compensating Ekman’s transport with return flow opposite
by direction to the prevailing wind (Hinrichsen et al., 2000). The halocline ascending
in the peripheral Gdansk Deep in 1994 and 1999 is likely explained by appearance of
these compensating flows.
Importance of these processes in sprat recruitment success is probably depends
on nutrients horizontal transport with water intruded from the open sea cold
intermediate layer into the coastal zone during spring and summer. Such water
intrusions were recorded in May and July 1999 and May 1994. No hydrographic
observations were carried out in July 1994, however some indirect indications
(Karasiova et al., 2002, this session) show that such water intrusions could occur in
summer 1994.
In the Baltic Sea the most of nutrients are found below the halocline; their
maximum in the surface layer is observed in winter. According to Yurkovski and
Rugane (1980) during summer minimum of phosphorus in the upper layer, its vertical
distribution has a specific form determined by availability of the intermediate zone
between thermo- and halocline, where phosphates are retained and accumulated.
These authors noted the spring maximum of organic phosphorus in the halocline.
Intensification of the vertical turbulent diffusion as a result of upwelling and
subsequent horizontal transportation of nutrients into the coastal zone seems to
become a necessary stage of the Baltic water nutrient enrichment including also
inflows of Kattegatte water, redistribution of deep-water reserves of nutrients during
stagnation and aeration alternation, winter convection mixing, river discharge, etc.
(Antonov, 1987; Nehring, 1980; Yurkovski, 1989). In turn, appearance of horizontal
gradient zones promotes accumulation of phyto- and zooplankton and creates
preconditions for the most efficient utilization of nutrients. According to Makarchouk,
Hinrichsen (1988) and STORE Consolidation Progress Report (2000) sprat larvae
vertical distribution in spring-summer was usually characterized by availability of
abundance peaks in the upper 10-m layer and in the upper or lower parts of the
halocline. Sprat larvae occurrence in the upper layer seems to be related to diurnal
vertical migrations. The returned compensating flows in the intermediate layer and
halocline may promote larvae transport towards the coast, however, water driving
winds causing upwelling at the eastern coast probably retain the most viable larvae
migrating vertically in the open-sea area. Abnormally high abundance of sprat larvae
observed in 1994 allows to assume the formation of hydrodynamic structures like
eddies, causing larvae accumulation and probably their high survival in the spawning
grounds. As a result of these processes during the years of intensive upwelling the
transport of nutrients into the coastal zone can fore-run the sprat larvae transport. On
contrary with prevailing westerly winds being moving surface water to inshore
direction the sprat larvae transportation into the coastal zone of the eastern Baltic
8
will accelerate, however will not be accompanied with nutrients inflow. It should be
noted that sprat larvae drift from the Gdansk Deep may also occur towards the
Gotland Deep, however finally sprat fry distribution in the late summer – early
autumn is associated primarily with the shallow zone both in Gdansk and Gotland
areas.
Despite significantly different hydrographic conditions in the near-bottom
layer of the deep-water Gdansk Deep in 1994 and 1999 (Zezera, 2001) including the
lower salinity and oxygen content and increased temperature in 1999 as compared to
1994, both years were characterized by the similar pattern of interaction between the
open and coastal parts of the Baltic Sea. This similarity is probably caused by the high
relatively recurrence of the same form of the atmospheric circulation and
corresponding winds during these years. It can be assumed that the increase of the
moderate easterly winds in spring and summer (including July) will promote active
upwelling off the eastern Baltic Sea coast and improve probability of young sprat
survival. For more efficient researches of these processes it is necessary to extend
scientific efforts undertaken in the open sea within the frames of various international
projects into the coastal zones of near-shore countries.
ACKNOWLEDGEMENTS
The author is grateful to Dr. D. Schnack, Dr. F.W. Koester, Dr. H. - H.
Hinrichsen, Dr. V. Feldman and A. Zezera for providing a possibility to participate in
R/V Alkor cruises under STORE Project, to process and use data set as well as for
useful discussions.
REFERENCES
Antonov A.E. 1987. Large- scale variability of the Baltic Sea hydrographic
regime and the latter impact on the fishery. L. Hydrometeoizdat. 248 pp.( in Russian).
Bychkova I.A., S.V. Victorov. 1987.Elucidation and systematization of
upwelling zones in the Baltic Sea based on satellite data. Oceanology, 27, 2:218 223.
Gidhagen, L.1984. Coastal upwellings in the Baltic - a presentation of satellite
and in situ measurements of sea surface temperatures indicating coastal upwellings.
In Proceedings of the 14 Conference of the Baltic Oceanographers, pp.182 - 190.
Gdynia. 849 pp.
Hinrichsen H. - H., M. St. John, E. Aro, P. Groenkjaer, and R. Voss.
2001.Testing the larval drift hypothesis in the Baltic Sea : retention versus dispersion
caused by wind - driven circulation. ICES Journal of Marine Science, 58: 973 - 984.
Koester F. W., Hinrichsen H.H., Schnack D., St.John M.A., MacKenzie B.R.,
Tomkiewicz J., Mollmann C., Plikshs M. And Makarchouk A. 2000. Recruitment of
Baltic cod and sprat stock: Identification of critical life stages and incorporation of
environmental variability and spatial heterogeneity into stock-recruitment
relationships. ICES CM 2000/N:16.
Kortum G. and A. Lehmann. 1997. A.V.Humboldts Forschungsfart auf der
Ostsee im Sommer 1834. Schr. Naturwiss. Ver. Schlesw. - Holst. Bd. 67, pp, 45 - 58.
Makarchouk A., Hinrichsen H.H. 1998. The vertical distribution of
ichthyoplankton in relation to the hydrographic conditions in the Eastern Baltic. ICES
CM 1998/R:11.
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Nehring D., 1987. Temporal variations of phosphate and inorganic nitrogen
compounds in central Baltic deep waters. Limnol. Oceanogr., 32:494-499.
Raid T. 1989. The influence of hydrodynamic conditions on the spatial
distribution of young fish and their prey organisms. Rapp. P. –v. Reun.
Cons.int.Explor. Mer., 190:166-172.
Ustinova L.A., Shvetsov F.G., 1986. On the method of investigation of young
sprat abundance and distribution. Fischerei –Forschung, 24. 2: 43-46.
Yurkovsky A.K., Rugane I.O. 1980. The ways and mechanisms of phosphorus
redistribution in the Gotland basin of The Baltic sea. Fischerei –Forschung, 18. 2: 8995.
Zezera A.S. 2001. Main features of the south-eastern Baltic sea hydrological
regime in 2000 and the latest retrospectives. ICES CM 2001/W:21.
10
56.5°
56.5°
55.5°
55.5°
5.0
54.5°
54.5°
18.5°
19.5°
20.5
18.5°
A
19.5°
20.5
B
56.5°
56.5°
55.5°
55.5°
54.5°
54.5°
18.5°
19.5°
20.5
18.5°
19.5°
C
20.5
D
56.5°
56.5°
1
20
55.5°
55.5°
1
54.5°
18.5°
19.5°
I
20.5°
54.5°
18.5°
19.5°
20.5°
F
Fig. 1. The spatial distribution: А - T °C at 20 м ; B - T °C at 70 м;
C - salinity at 70 м; D - water density at 70 м; I - sprat eggs (sp/m2);
F - sprat larvae (sp/m2). 15.04. - 09.05. 1993
11
56.5°
56.5°
55.5°
55.5°
54.5°
54.5°
19°
20°
21°
19°
А
20°
21°
B
56.5°
56.5°
55.5°
55.5°
3.5
54.5°
54.5°
19°
20°
C
21°
19°
20°
D
Fig. 2. The spatial distribution: А - T °C at 20 м; B - water density at 20 м;
C - T °C at 40 м; D - T °C at 70 м. 24.05.-02.06.1994
21°
12
56.5°
56.5°
55.5°
55.5°
54.5°
54.5°
19°
20°
21°
19°
А
20°
21°
B
56.5°
56.5°
55.5°
55.5°
54.5°
54.5°
19°
20°
C
21°
19°
20°
D
Fig.3. The spatial distribution: А - salinity at 70 м; B - water density at 70 м;
C -sprat eggs (sp/m2); D - sprat larvae (sp/m2).
24.05-02.06 1994
21°
13
56.5°
56.5°
55.5°
55.5°
54.5°
18.0°
19.0°
20.0°
54.5°
18.0°
A
56.5°
55.5°
55.5°
19.0°
C
20.0°
B
56.5°
54.5°
18.0°
19.0°
20.0°
54.5°
18.0°
19.0°
20.0°
D
Fig. 4. The spatial distribution: А - T °C at 20 м; B - T °C at 70 м; С - salinity at 70
м; D - water density at 70 м. 23.05-02.06.1998
14
56.7°
56.7°
56.7°
55.7°
55.7°
55.7°
54.7°
18.3°
19.3°
20.3°
54.7°
18.3°
А
19.3°
20.3°
54.7°
18.3°
B
56.7°
56.7°
55.7°
55.7°
55.7°
19.3°
D
20.3°
54.7°
18.3°
19.3°
I
20.3°
C
56.7°
54.7°
18.3°
19.3°
20.3°
54.7°
18.3°
19.3°
20.3°
F
Рис. 5. The spatial distribution: А - T°C at 20 м; B - T °C at 40 м; C - T °C at 70 м; D - oxygen content (ml/l) at 70 м; I - salinity at 70 м;
F - water density at 70 м. 11-15.07. 1998
15
18.5°
19.5°
18.5°
19.5°
55.5°
55.5°
55.5°
55.5°
55.0°
55.0°
55.0°
55.0°
18.5°
19.5°
18.5°
19.5°
A
18.5°
B
19.5°
18.5°
19.5°
55.5°
55.5°
55.5°
55.0°
55.0°
55.0°
55.0°
20
55.5°
40
18.5°
19.5°
C
18.5°
19.5°
D
Fig. 6. The spatial distribution: A - sprat eggs (sp/m2), 23-24.05.98; B - sprat larvae (sp/m2), 23-24.05.98;
C - sprat eggs (sp/m2), 10-12.07.98; D - sprat larvae (sp/m2), 10-12.07.98
16
19°
20°
19°
20°
19°
56°
56°
56°
56°
55°
55°
55°
55°
19°
20°
19°
А
19°
56°
55°
55°
19°
20°
B
20°
19°
C
20°
56°
56°
56°
56°
55°
55°
55°
55°
55°
20°
D
19°
20°
I
20°
19°
56°
19°
20°
56°
20°
19°
56°
55°
20°
F
Fig. 7. The spatial distribution: А - T °C at 20 м; B - T °C at 40 м; C - T °C at 70 м; D - oxygen content (ml/l) at 70 м; I - salinity on 70 м;
F - water density at 70 м. 08-15.05 1999
17
18°
19°
20°
55.5°
18°
19°
20°
55.5° 55.5°
54.5°
55.5°
54.5° 54.5°
18°
19°
20°
54.5°
18°
А
18°
19°
20°
19°
20°
B
19°
20°
55.5°
18°
55.5° 55.5°
54.5°
55.5°
54.5° 54.5°
18°
19°
C
20°
54.5°
18°
19°
D
Fig. 8. The spatial distribution: А - T °C at 20 м; B - T °C at 70 м;
C - salinity at 70 м; D - water density at 70 м.
28.05-01.06. 1999
20°
18
18.5°
19.5°
18.5°
19.5°
18.5°
19.5°
55.5°
55.5°
55.5°
55.5°
55.5°
55.5°
55.0°
55.0°
55.0°
55.0°
55.0°
55.0°
18.5°
19.5°
18.5°
А
18.5°
19.5°
18.5°
B
19.5°
18.5°
19.5°
C
19.5°
18.5°
19.5°
55.5°
55.5°
55.5°
55.5°
55.5°
55.5°
55.0°
55.0°
55.0°
55.0°
55.0°
55.0°
18.5°
19.5°
D
18.5°
19.5°
I
18.5°
19.5°
F
Fig. 9. The spatial distribution: А - T °C at 20 м; B - T °C at 40 м; C - T °C at 70 м; D - oxygen content at 70 м; I - salinity at 70 м,
F - water density 70 м. 03-05.07 1999
19
19°
20°
56°
19°
56°
55°
55°
19°
20°
55°
19°
55.5°
55.0°
55.0°
19.5°
D
55.5°
55.0°
55.0°
18.5°
B
18.5°
19.5°
18.5°
55.5°
20°
А
55.5°
19.5°
56°
55°
20°
18.5°
18.5°
56°
19.5°
C
19.5°
18.5°
19.5°
55.5°
55.5° 55.5°
55.5°
55.0°
55.0° 55.0°
55.0°
18.5°
19.5°
I
18.5°
19.5°
F
Fig. 10. The spatial distribution: А - sprat eggs (sp/m2), 08-15.05; B - sprat larvae (sp/m2), 08-15.05;
C - sprat eggs (sp/m2), 27-31.05; D - sprat larvae (sp/m2), 27-31.05; I - sprat eggs (sp/m2), 03-05.07; F - sprat larvae (sp/m2), 03-05.07
20
Н, м
0
Н, м 0
Н, м
7.0
-10
0
5.0
7.0
5.0
4.5
-10
-10
-20
-20
-30
-30
5.5
-20
4.0
-30
-40
-40
-50
-40
-50
-60
-50
7.5
6.0
-60
-70
4.5
-90
65
63
64
66
62
№ ст
S‰
9.0
-90
64
65
63
66
№ ст
62
№ ст
1a
8.0
63
62
Н, м
0
9.0
8.5
-10
7.0
-10
-20
5.5
-20
-20
-30
-30
3.5
4.0
-30
64
1c
0
Н, м
9.5
7.5
65
1b
Н, м 0
-10
8.0
8.5
-80
11.5
-90
66
7.5
10.0
10.5
11.0
-80
5.0
7.0
-70
9.0
Т°С
-80
6.5
8.5
4.0
-70
-60
8.0
3.0
-40
-40
-50
-50
-60
3.5
3.0
4.0
-40
-50
7.5
8.0
-60
4.5
9.0
10.0
10.5
-70
-70
11.0
Т°С
-70
S‰
11.5
4.0
5.0
-80
-60
8.5
-80
-80
9.5
12.0
-90
-90
-100
-100
5
№ ст
4
10
3
12.5
4
3
10
1
2c
Н, м
Н, м
-10
9.5
10
3
2b
Н, м
-10
7.0
8.5
-20
4
5
1
№ ст
2a
-10
10.5
-100
5
№ ст
1
-90
13.0
-30
7.0
-20
6.5
-20
7.5
5.5
5.5
4.5
4.0
-40
-50
-30
-30
-40
-40
-50
-50
7.5
-60
-60
4.0
-70
4.5
8.0
8.5
-60
6.0
-70
7.0
6.5
9.0
-70
5.0
5.5
-80
6.5
-90
-80
-90
8.5
12.0
12.5
-100
79
80
70
72
79
№ ст
9.0
-90
S‰
7.0
Т°С
-100
7.5
8.0
-80
6.0
80
9.5
-100
72
79
70
80
3a
3b
-10
70
3c
Н, м
Н, м
72
№ ст
№ ст
Н, м
-10
-10
14.0
-20
-20
-30
-30
-30
-40
-40
-40
-50
-50
-20
13.5
5.0
5.5
5.0
-50
4.0
-60
-60
-70
-70
5.0
-80
78
81
12.0
-100
7.0
82
-100
77
78
№ ст
4a
9.0
-90
S‰
Т°С
77
№ ст
-80
-90
-100
6.0
-70
-80
6.0
-90
-60
7.5
8.0
81
82
77
78
81
82
№ ст
4b
4c
Fig. 11. The vertical distribution of isoterms (a), isohalines (b) and isopycnics (с) at cross transect
in the Gdansk Deep:
1.55°05 N, 18°45 E — 55°05 N, 19°50 E, 30.04.-01.05. 93
2. 55°10 N, 19°09 E — 54°34 N, 19°40 E, 24-25. 05. 94
3. 55°10’ N, 18°49 E — 54°48’ N, 19°23 E, 23-24. 05. 98
4. 55°10’ N, 18°49 E — 54°48’ N, 19°25 E, 9-11.07. 98
21
H, м 0
5.38
6.83
5.10
6.67
H, м 0
-10
7.09
6.91
7.02
6.77
7.0
7.0
7.0
-20
5.27
5.5
5.5
-20
-30
-30
-30
4.5
-40
-40
-40
4.0
3.5
3.5
-50
-50
-50
3.0
-60
-60
6.0
-60
-70
-70
4.0
-70
-80
S‰
-80
5.5
8.5
-80
-90
-90
-100
-90
-100
14
15
№ ст
13
15
12
14
№ ст
1a
10.0
5.0
-40
4.0
-50
3.5
3.0
-60
3.0
-20
-30
-30
-40
-40
-50
-50
-60
-70
8.5
9.5
5.0
-80
10.5
T°C
8.5
-90
-90
S‰
-100
9.0
11.5
-100
-100
-110
-110
98
89
92
93
89
92
93
№ ст
2a
98
№ ст
93
2b
0
Н, м
18.0
16.0
-10
12.0
-20
8.0
-30
Н, м
-20
5.5
-30
-40
-50
-50
6.0
6.0
7.5
3.0
-60
3.5
-60
6.5
7.0
7.5
8.0
8.5
4.0
9.5
-70
5.0
4.5
5.0
7.0
-40
4.0
3.5
4.0
-10
-30
6.0
-40
0
-20
10.0
-70
8.5
10.5
Т°С
-80
-80
11.0
S‰
-80
-90
-90
6.0
-100
9.0
-100
-100
-110
-110
56
52
50
49
№ ст
7
56
52
50
49
7
56
52
50
49
7
№ ст
№ ст
3a
89
92
2c
-10
14.0
-90
6.5
7.5
-80
6.0
-70
4.586
7.5
-70
-80
-60
4.601
-10
-20
-60
4.0
-70
98
№ ст
12
5.5
6.0
-30
13
4.587
5.094
Н, м 0
7.0
-10
9.0
8.0
-20
-50
14
1c
Н, м 0
13.0
12.0
11.0
-90
15
№ ст
12
13
1b
Н, м
-10
7.5
7.0
6.5
T°C
4.5
Н, м
5.54
-10
-10
6.0
5.0
5.0
-20
5.64
5.37
Н, м 0
3b
3c
Fig. 12. The vertical distribution of isoterms (а), isohalines (b) and isopycnics(с) at cross transect in
the Gdansk Deep:
1. 55°22’5 N, 19°04’2 E — 55°22’5 N, 20°09’5 E, 11.05.99
2. 55°38 N, 19°11 E — 54°47 N, 19°26 E, 30-31. 05. 99
3. 55°17 N, 19°06 E — 54°52 N, 19°43 E, 04-06. 07. 99
22
10.0
10.0
55.5°
400
55.5°
400
300
300
200
200
100
100
0
0
eggs
54.5°
larvae
54.5°
19°
20°
19°
isohaline
A
20°
isohaline
B
1100
120
1000
55.5°
900
100
55.5°
800
80
400
60
300
40
200
20
100
10
0
eggs
0
larvae
54.5°
19.0°
20.0°
isohaline
C
54.5°
19.0°
20.0°
isohaline
D
Fig.13.Sprat eggs and larvae (sp/m2) distribution
according to isohaline locations at 70 m depth level:
A-eggs; B-larvae 24-29.05.1994;
C-eggs D-larvae 29.04 -09.05.1993
23
55.5°
55.5°
1100
50
1000
700
30
500
400
10
300
55.0°
200
55.0°
5
100
0
0
larvae
eggs
18.5°
19.5°
18.5°
isohaline
А
isohaline
19.5°
В
600
55.5°
500
40
55.5°
30
400
20
300
10
200
5
55.0°
100
55.0°
2
0
0
eggs
18.5°
19.5°
isohaline
C
larvae
18.5°
19.5°
isohaline
D
Fig.14.Sprat eggs and larvae (sp/m2) distribution
according to isohaline locations at 70 m depth level:
A-eggs; B-larvae 23-24.05.1998;
C-eggs; D-larvae10-12.07.1998
24
56°
56°
400
70
300
9.
5
250
150
7.5
90
30
7.5
20
50
30
55°
10
55°
10
0
0
larvae
eggs
19°
20°
19°
isohaline
20°
isohaline
A
B
1200
100
1050
55.5°
55.5°
90
900
750
80
600
60
450
40
300
55.0°
150
55.0°
20
0
0
eggs
18.5°
larvae
19.5°
18.5°
isohaline
C
isohaline
19.5°
D
55.5°
55.5°
25
700
15
600
10
500
55.0°
400
55.0°
5
0
larvae
300
eggs
18.5°
19.5°
isohaline
I
18.5°
19.5°
isohaline
F
Fig.15.Sprat eggs and larvae (sp/m2) distribution
according to isohaline locations at 70 m depth level:
A-eggs; B-larvae, 08-15.05.1999;
C-eggs; D-larvae, 27-31.05.1999;
I-eggs; F-larvae, 03-05.07.1999
25
Table 1
Location depths (m) of 8 psu isohaline and the upper and lower 4 °C isotherms in the western and eastern parts of the Gdansk Deep
Year
Month
Delta, м
The western part
The eastern part
55°22'N-55°00'N, 19°00'E-19°10'E
55°05'N-54°47'N, 19°23'E-19°35'E
8 psu
4 °C upper
4 °C lower
8 psu
4 °C upper
4 °C lower
8 psu
4 °C upper 4 °C lower
isohaline
isotherm
isotherm
isohaline
isotherm
isotherm
isohaline
isotherm
isotherm
1993
early May
61.8
21.3
68.4
65.8
20.7
71.4
-4.3
+0.6
-3.0
1994
late May
68.1
26.6
73.0
57.3
18.9
61.7
+10.8
+7.7
+11.3
1998
late May
66.5
45.1
66.8
66.8
44.8
68.6
-0.3
+0.3
-1.8
early July
70.7
49.7
70.0
72.4
50.0
71.8
-1.7
-0.3
-1.8
early May
73.2
28.6
76.2
62.0
30.9
64.1
+11.2
-2.3
+12.1
late May
71.3
44.2
72.6
67.0
29.5
69.7
+4.3
+14.7
+2.9
early July
71.1
41.5
73.4
63.6
42.2
67.0
+7.5
-0.7
+6.4
1999
26
Table 2
The Baltic sprat early developmental stages abundance (sp/м2) in the Gdansk Deep
(54°54' - 55°30' N, 18°45' - 19°40' E at depth ≥70 m) in May and the sprat recruitment strength
characteristic in 1993, 1994, 1998, 1999
Year
Date
Sprat eggs
Sprat larvae
Sprat recruitment
strength characteristic
1993
01-09.05
504.2
25.7
poor
1994
24-28.05
254.4
233.0
strong
1998
23-24.05
656.4
16.5
poor
1999
28-30.05
548.0
38.9
strong