Vulnerability of parrotfish functional diversity and coral reef
health in transitioning island socio-ecosystems
Katherine R Rice Corresp.
1
1
Department of Environmental Science, Policy, and Management, University of California, Berkeley, Berkeley, California, United States
Corresponding Author: Katherine R Rice
Email address: [email protected]
Mo’orea’s reefs have rebounded from environmental disturbance throughout the years
largely due to herbivorous fish that deter damaging algal blooms. This resilience suggests
herbivorous fishes act as a keystone species in the coral reef ecosystem, and the greater
island community of Mo’orea. Parrotfish support reef health and stability, and reefs
support the development of the local economy by way of tourism and access to medicine,
nourishment, and protection. Because island communities rely heavily on coral reef
ecosystems, identifying the impact of fishing on the morphology and ecosystem function
of parrotfish in a time of marine management and demographic transition can increase our
knowledge of the vulnerability and resilience of these complex socio-ecosystems. The
2016 study reported here seeks to understand to what extent changes in fisheries
management and off-take rates have affected the historically sustainable relationship
between Mo’orea’s fishing population, the lagoon’s supply of larger-sized parrotfish, and
the ecological stability of the greater coral reef ecosystem. Specifically, this study
measured average parrotfish size at various fishing zones and paired Marine Protected
Areas (MPAs) around the island, and then used participatory surveys to quantify fishermen
observation of changes in parrotfish size since they started fishing. Both field data and
participatory survey data show a decrease in parrotfish size since the establishment of
MPAs. Island-wide, parrotfish also appear to be smaller in fished sites than in MPAs. Results
suggest that the joint effect of zoning, catch-size enforcements and increased fishing
pressure have caused a size-selection of parrotfish in the fishing zones of studied lagoons.
These findings highlight the vulnerability of Mo’orea’s coral reef ecosystem to transitions in
marine management strategy and size-selective fishing.
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Vulnerability of parrotfish functional diversity and coral
reef health in transitioning island socio-ecosystems
Katherine Rose Rice1
1 Department
of Environmental Science, Policy, and Management, University of California, Berkeley,
Berkeley, CA, USA
[email protected]
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Introduction
Coral reef ecosystems are fundamentally important to many Pacific Island countries and
inhabitants, including those in the South Pacific (Ferraris and Cayré, 2003; Kronen et al., 2010;
Moberg and Folke, 1999; Dalzell et al., 2006). Coral reefs support the development of local and
national economies by providing goods and services to island communities via fisheries (Moberg
and Folke, 1999). Reefs, however, are becoming critically threatened by overfishing as a result
of overexploitation of commercial fish (Hughes et al., 2003, 2007; Pandolfi, 2003; Bellwood et
al., 2006; Dalzell et al., 2006; Jackson et al., 2001). Unsustainable tampering with the reef’s
balance of biological diversity has serious consequences for the goods and services that humans
derive from coral reef ecosystems. Consequences include species extinction, reduced ecosystem
resilience (i.e. the capacity of an ecosystem to tolerate disturbance without collapsing into a
qualitatively different state), and phase shifts from coral to algal dominance (Bellwood et al.,
2005; Norström et al., 2009; Wilson et al., 2008; Hughes et al., 2010; Jennings and Polunin,
1996; Jennings and Lock, 1996; Jennings and Kaiser, 1998; Wilder, 2003).
The declining health of coral reef ecosystems worldwide has serious implications for their
capacity to persist in an era of rapid global change. Reefs have lost their capacity to endure
recurrent natural disturbances, and some have undergone long-term phase shifts to degraded
ecosystems dominated by fleshy seaweed or other macroalgae (Bellwood et al., 2005; Norström
et al., 2009; Wilson et al., 2008; Hughes et al., 2010). Interestingly, however, coral reefs
surrounding Mo’orea have historically returned to coral dominance following major
environmental disturbances without shifting to a macroalgal-dominated state (Adam et al., 2011).
Adam and colleagues (2011) found that the increased algal growth associated with coral loss
prompts the response of herbivorous fishes, particularly parrotfish, to graze the reef and
consequently help coral reefs recover. Wilder (2003) similarly concluded that if herbivore stocks
were reduced to low levels through fishing pressure, reefs could be overgrown quickly by dense
algae on a short time scale. Adam (2011) highlighted the importance of parrotfish ecosystem
function in maintaining reef resilience in the face of disturbance, and Wilder (2003) revealed the
vulnerability of the reef ecosystem to declines in herbivore density. In addition, previous studies
have identified herbivorous fish as important factors in regulating algal biomass, cover, and
composition on coral reefs (Jennings and Polunin, 1996; Jennings and Lock, 1996; Jennings and
Kaiser, 1998).
The functional diversity within parrotfish populations has been suggested to be a result of
differing morphologic characteristics, such as body size (Lokrantz et al., 2008; Bruggemann et
al., 1994; Littler et al., 1989; Roff et al., 2011). Populations of large parrotfish are characterized
by intense grazing behavior and can harvest the surface of each square meter of reef every 18
days, removing up to 40 kg of algae from each square meter per year (Hoey and Bellwood,
2008). In addition to grazing capacity, parrotfish size has also been found to be representative of
reproductive capacity (Barba, 2010; Choat and Bellwood, 1998; Thresher, 1984). Terminal phase
males dominate reproductive activity through a harem-based social system and can be either
primary, i.e., born male, or secondary, i.e., females that have undergone sex change (Choat and
Bellwood, 1998; Thresher, 1984). Terminal males are usually the largest of the population
(Choat and Bellwood, 1998; Thresher, 1984). Larger parrotfish are thus especially critical in
sustaining population size and coral reef ecosystem balance.
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Fishing pressure in the Pacific Islands is strongly tied to human population density (Jennings and
Kaiser, 1998; Russ and Alcala, 1989). In addition, increases in fishing pressure result in changes
in target populations (Jennings and Lock, 1996) and in the island fishing community (Jennings
and Polunin, 1996). Population census figures for Mo’orea between 1971 and 2007 show an
average annual population growth rate of 2.39%, which is higher than the rate for French
Polynesia as a whole (1.57%) (Leenhardt et al., 2016). This increase in population implies a
respective increase in demand of natural resources, particularly fish from the lagoon, as this is
where recreational and subsistence fishing activity is concentrated (Leenhardt et al., 2016; Lison
de Loma, 2005). In fact, transition in the demography of French Polynesia has led to a decrease
in the density and biomass of harvested fish yields in Mo’orea and Tahiti (which are more
heavily fished) (Lison de Loma, 2005). These data suggest that increased fishing pressure may
be generally depleting fish stocks, and specifically taking larger individuals thereby impairing
the ability of the population to reproduce. Thus, the transitioning socio-ecosystem of Mo’orea
presents a model for studying the vulnerability of fish size and abundance to increasing fishing
pressure. A favored commercial catch and a dominant herbivore of the lagoon, parrotfish, family
Scaridae, represent a fish important to both the sociology and ecology of Mo’orea’s island socioecosystem. Parrotfish are thus an applicable bio-indicator for understanding the sociological
impact of changes in fishing pressure, and the ecological response of reef stability and resilience.
Effects of overfishing in Mo’orea were first noticed in 1991 when local citizens and foreign
scientists observed that the sizes of fish and overall catches in Mo’orea’s lagoon were declining
over time (Walker and Robinson, 2009). As a small-scale fishing community dependent on
fishing for income and subsistence (Leenhardt et al., 2016; Walker, 2001), and as a scientific
model of an unspoiled island ecosystem for many researchers, concerns about overfishing from
local communities, territorial services (Fisheries, Environment, Urbanism), scientific research
institutions, and local politicians led to the implementation of a comprehensive marine
management plan (Salvat and Aubanel, 2002). The Plan de Gestion de l’Espace Maritime
(PGEM) for Mo’orea was established in 2004 and encompassed the entire lagoon and all waters
beyond the reef crest out to the 70-m isobath on the outer reef slope (PGEM, 2005). The PGEM
established a network of eight “no-take” zones referred to as Marine Protected Areas (MPAs)
covering approximately 20% of the lagoon, and enforced size and catch limits on commercial
fish species throughout the fishing zones of the lagoon (Walker and Robinson, 2009).
The implications of dividing the lagoon have both spatial and temporal components (Francour,
2000). The spatial components include differences between protected and unprotected zones,
such as fishing pressure and the presence of size and catch limits (Russ and Alcala, 1989;
Harmelin-Vivien et al., 1995; Francour, 2000). The temporal components include differing
ecological responses between the protected no-take MPA reserves and the unprotected fishing
zones of the lagoon (Francour, 2000). While no-take MPA reserves establish points of reference
to assess human and other impacts on adjacent marine environments, this study suggests that the
MPA reserve management strategy may induce additional unanticipated spatial and temporal
components for small-scale island fisheries such as Mo’orea’s lagoon. As an island only 61 km
in circumference and heavily dependent on fishing, Mo’orea’s fishery is already limited. No-take
reserves redistribute fishing pressure to spatially concentrated fishing zones. In addition to
increases in fishing pressure as a result of zoning, catch-size regulations on commercial fish
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increase pressure on larger bodied fish. For parrotfish, the PGEM’s catch-size regulations
encourage catch of the more functionally and socially important individuals (>25 cm), thus
failing to consider the ecosystem function and complex socio-sexual system of large-bodied
individuals (PGEM, 2005; Lokrantz et al., 2008; Choat and Bellwood, 1998; Thresher, 1984).
While the Centre de Recherches Insulaires et Observatoire de l’Environnement (CRIOBE) has
monitored the biological effects of the MPAs since 2004 (Lison de Loma et al., 2008),
CRIOBE’s monitoring plan doesn’t address the PGEM’s effect on fishing pressure and the
vulnerability of the collective reef ecosystem to human-derived transitions in management.
Size-selective fishing pressure from catch-size regulations and an increasing fishing industry
mark two notable deviations from Mo’orea’s historically synchronized socio-ecosystem (Adam
et al., 2011). Given the social and ecological components of Mo’orea's transitioning lagoon
fisheries, understanding their dual dynamics requires integrated methods that consider both
systems simultaneously (Jennings and Kaiser, 1998). Pairing ecological field surveys with
participatory monitoring techniques allows for comparison of how fishermen understand and
interact with their lagoon, and how the lagoon responds to their understanding of its supply of
resources. Filling these gaps in our knowledge will enhance the development of marine resource
management initiatives that seek long-term sustainability of reef fisheries and foster ecosystem
resilience. To promote an understanding of the impact of size-selective fishing pressure on the
vulnerability of a small-scale fishery’s coral reef ecosystem, this study compares parrotfish size
and abundance in exploited fishing zones and MPAs around the island. To better evaluate the
sustainability of the existing fishery, this study also includes a participatory monitoring of 50
local fishermen from around the island. Specifically, this study seeks to quantify the increasing
population of Mo’orea’s fishing community, and assesses how increase in lagoon resource
demand, in conjunction with the PGEM’s zoning and catch-size enforcements, is leading to sizeselection of parrotfish in Mo’orea’s lagoon.
Methods
Study sites
Fieldwork was conducted in lagoons on the island of Mo’orea, French Polynesia from October to
November, 2016 (Fig. 1). Mo’orea is a volcanic island with 61 km of coastline, encircled by a
barrier reef, which forms a 30-km2 lagoon ranging from 500 to 1500 m in width (Galzin, 1985).
To calculate the extent to which size-selective fishing pressure impacts parrotfish size in fishing
zones of the lagoon, this study conducted transects along a gradient of MPA’s and non-protected
fishing zones. Five MPAs (Temae (P1), Pihaena (P2), Tetaiuo (P3), Tiahura Motu (P4), and
Afareaitu (P5)) were chosen based on accessibility and proximity to corresponding paired fished
sites (F1, F2, F3, and F5) (Fig. 1). The paired sites have close proximity and similar
geomorphologies. However, MPA Tiahura Motu and MPA Tetaiuo are geomorphologically
similar so a single fishing site in between these two MPAs was chosen (F3) (Fig. 1). The nine
survey sites represent geographic diversity and are distributed along the northwestern, northern,
and northeastern coasts of the island. Sites were selected to encompass a range of human
activity, human development, fishing pressure, and fish density. Other parameters used to choose
sites include depth and sea floor composition.
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Field Sampling Methods
Transects (described below) were conducted on two occasions, each in a period of ten days
around two principal lunar phases: one during the full moon and one during the new moon to
account for potential lunar variation (Galzin, 1987). Observations were always made between
0900 and 1630 hours (local time), to minimize any heterogeneity caused by diel variation in fish
behavior (Galzin, 1987).
Five locations around the island were sampled during each lunar occasion. Pairs of sites (MPA
and fished) were sampled within each location on the same day (with exception of Tetaiuo and
Tiahura Motu, which shared a fished site and were all sampled on the same day). Two distinct
reef habitats were sampled at each site: the fringing reef close to shore and the back reef towards
the reef crest. Three stations were surveyed per reef habitat, yielding a total of 54 stations: nine
sites (five MPAs, four fished sites) x two habitats x three stations per habitat, and 108 surveys
(54 stations x two lunar occasions).
Transect lines were 30 m long and aligned parallel to shore. When surveying at motus, transects
were aligned parallel to the motu. In absence of fixed markers, each station was located using a
handheld global positioning system (GPS) receiver. Situational characteristics including presence
of fishermen, boat traffic, swimmers, current strength, or intense weather conditions were also
recorded at each site.
Preliminary surveys revealed high diversity of parrotfish species (>12 species) at each station, so
for simplicity parrotfishes were identified at the family level (Scaridae), counted, and body
length estimated to the nearest centimeter using a ruler for scale (counts and average body
lengths were recorded for schools of fishes). Transect lines were surveyed continuously by
swimming at a slow steady speed (10m/min) to observe fishes in an undisturbed state.
Fishing Population Surveys
To indirectly estimate change in average parrotfish size throughout time, this study used a
participatory monitoring survey method, drawing upon 50 local fishermen of all ages, genders,
and villages around the island as ecological monitors. The survey asked participants to quantify
any changes in parrotfish size throughout their lifetime as a fisherman. Size estimates from 1956
to 2013 were derived and compared to the average of size estimates from 2016. Individual
estimates were plotted on a graph to reveal the island’s collective understanding of parrotfish
size over a timescale of 60 years. Estimates of parrotfish body size from 1956 to 2013 were also
compared to changes in human population from 1956 to 2013 to look for potential correlation
and provide additional evidence for the effect of increases in human population on reef
vulnerability.
Data Analyses
This study’s aim is to estimate how decreases in parrotfish body size and abundance (functional
diversity) may vary between MPA and fished sites. In addition to site, this study considers how
functional diversity is affected by location, habitat, and moon phase. From field observations, the
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vulnerability of parrotfish to size-selective fishing pressure is estimated on varying spatial and
temporal scales. This study used R Studio software (R Core Team, 2013) for all statistical
analyses.
Fish size and abundance were analyzed across replica transects for 108 stations. Size data fulfill
the assumptions of parametric statistics (normal distribution, similar sample sizes, and equal
variances) (Fig. 2); however, abundance data are not normally distributed. To test for differences
in mean total parrotfish size between sites (grouped among MPAs or fished), reef habitats
(grouped among fringing or back), location (1, 2, 3, 4, or 5), and lunar occasion (full moon or
new moon), a four-way analysis of variance (ANOVA) followed by a Tukey HSD post-hoc test
were run using these four variables as predictor variables and fish size as the response variable
(results shown in Table 1). To analyze fishing pressure’s effect on parrotfish abundance, a
Kruskal Wallace test was run for the variable location, and Wilcoxon rank sum test with
continuity correction was run for site, reef habitat, and lunar occasion.
Results
Field sampling
Site
Island-wide, average body size is greater in MPAs (26 cm ± 4 cm) than in fished sites (24 cm ± 5
cm) (p<0.001) (Fig. 3). Post-hoc comparisons using the Tukey HSD test, however, indicated that
the average body size is only larger in MPA sites than in fished sites for Locations 1 and 5
(p<0.05, p<0.05). In addition to larger average body size in MPAs, parrotfish are more abundant
in MPAs (31 ± 61 fish) than in fished sites (12 ± 16 fish) (p<0.05) (Fig. 4).
Location
Regardless of site, however, average body size also differs between locations (Fig. 3 & 5).
Average body size in Location 1 (22 cm) is smaller than average body size in Location 3 (26
cm), 4 (29 cm), and 5 (26 cm) (p<0.001, p<0.001, p<0.001). In addition, average body size in
Location 2 (24 cm) is smaller than average body size in Locations 4 and 5 (p<0.001, p<0.05).
Average body size in Location 4 is larger than average body size in Locations 3 and 5 (p<0.05,
p<0.001). Contrary to size, parrotfish abundance does not significantly differ among locations
(p=0.10) (Fig. 4 & 6).
Habitat
Island-wide, parrotfish are larger in back reef habitats in both MPA (Back: 26 cm, Fringing: 24
cm) and fished sites (Back: 26 cm. Fringing: 22 cm) (p=0, p<0.05) (Fig. 3). Post-hoc
comparisons using the Tukey HSD test, however, reveal average body size isn’t larger in back
reef habitats for all locations. Body sizes are only larger in back reef habitats for Locations 1
(p=0), 2 (p=0), and 5 (p=0). Parrotfish are also larger in MPA sites (24 cm) than fished sites (22
cm) in all fringing reef habitats (p=0) (Fig. 7). Contrary to size, parrotfish abundance does not
significantly differ between habitat types (p=0.22) (Fig. 4).
Lunar Occasion
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Island-wide, average body size differs according to lunar occasion sampled (Fig. 3 & 5).
Average parrotfish are larger when surveyed on the full moon (26 cm) compared to surveys on
the new moon (25 cm) (p<0.001). Post-hoc comparisons using the Tukey HSD test indicate
average size is larger during the full moon than the new moon for Locations 1 and 5 (p=0,
p<0.05), but smaller during the full moon for Location 2 (p<0.05). Larger parrotfish in both
fished and MPA sites (p=0.01, p<0.005) are observed during the full moon, in comparison with
the new moon. During the new moon, parrotfish are also always larger in MPAs than fished sites
(p<0.05); however, during the full moon, there is no difference in observed sizes between sites.
Contrary to size, parrotfish abundance does not significantly differ between lunar occasions
(p=0.88) (Fig. 4 & 6).
When no fish were observed in a single transect, fish abundance and size were not recorded, so
some habitats only represent one or two stations out of the total three stations surveyed. When a
site didn’t physically have one of the two habitat types due to island geomorphology, only the
habitat type present was sampled for fish (Fig. 7).
Fishing Population Surveys
Results are derived from participatory survey answers provided by 50 fishermen. Surveyed
fishermen range from 18 to 81 years of age, include males and females, include residents from
every village around the island, and were all surveyed independently to avoid preconceptions.
Average parrotfish size was noted to decrease throughout the lifetimes of 39 out of the 50
surveyed fishermen (Fig. 8). Noted decreases in size range according to the year fishermen
started fishing, varying from 5 to 30 cm. Despite the differing timescales of observations,
however, the average change in parrotfish size as perceived by fishermen is 9 cm. The average
parrotfish size today is 23 cm ± 8 cm (p<0.001), compared to an average size estimate of 32 cm
± 10 cm by fishers who started their fishing career between 1956 and 2002 (p<0.001).
Subsequently, while almost every fisherman estimated parrotfish were 20 cm or larger at the start
of their fishing career, only 32% of fishermen estimated that parrotfish were 20 cm or larger in
2016 (p<0.001) (Fig. 9).
Discussion
Previous studies have observed extreme transition over the past two to three decades in
Mo’orea’s coral reefs from hard-coral-dominated communities to communities now dominated
by fleshy algae (Galzin et al., 2016; Lamy et al. 2015). This type of phase shift has been
catalyzed by frequent disturbances, both natural and human derived, and reefs have been forced
to adapt quickly, exhibiting cycles of decline and recovery (Hughes et al., 2005; Adam et al.,
2011; Lamy et al. 2015). Researchers have suggested that phase shifts might be caused by
decreases in herbivore density and correspondingly reduced grazing (Galzin et al., 2016; Hughes,
1994; Wilder, 2003). Decreases in herbivore density have increased the susceptibility of the
lagoon to phase shifts, have led to a less resilient reef (Galzin et al., 2016; Adam et al., 2011;
Lison de Loma, 2005), and have consequently made the greater ecosystem exceptionally
vulnerable to disturbance. While environmental disturbances cannot be predicted, this study
obtained an awareness of the various human-derived stresses affecting the Mo’orea’s reef
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ecosystem. This study observed two major transitions in Mo’orea’s societal relationship with the
lagoon: increase in resource demand, and transition in lagoon management.
First, this study found an annual population growth rate of 3.79 from 1956 to 2012 on Mo’orea
(Fig. 10) (ISPF, 2015), implying increased demand for fish around the lagoon. Roadside fish
stands and personal communication with 50 surveyed fishermen revealed the high demand for
parrotfish in particular (Rice, 2016, Personal observation). In addition, both the fishing
demographic and the demand for parrotfish have increased since previous accounts (Aubanel,
1993; Brenier, 2009; Madi Moussa, 2010; Vieux, 2002; Yonger, 2002) The extent of this
increase, however, is difficult to measure, as supply and demand for fish meet along the roadside
rather than in the markets (Madi Moussa, 2010). Increases in fishing pressure are also unapparent
to the average fisherman because fish stocks are non-concentrated and fishing activity is spread
around the lagoon (Leenhardt et al., 2016). The combination of these circumstances suggests that
fishermen are unaware of their collective footprint on the lagoon ecosystem, and consequently,
demand for lagoon resources may be exceeding supply.
In addition to increase in resource demand by a growing island population, foreign stakeholders
have infiltrated management of the lagoon. Disregarding the complexities and uncertainties of
Mo’orea’s spatially and temporally dispersed fisheries as described above, recent management
practices have limited and regulated areas of the lagoon previously relied upon by fishermen as
sources of subsistence (Walker, 2001). Since the establishment of MPAs, protected areas of the
lagoon have seen increases in fish biomass (Lison de Loma et al., 2008); however, the effect of
concentrated activity in the fishing zones has been overlooked. Fishing zones have only been
used in research as ‘controls,’ assuming that MPAs are the only zones with a changing
ecosystem (Lison de Loma et al., 2008; Lamy et al., 2015). This study, however, reveals that
transitions in lagoon management, including zoning and catch-size regulations, affect the entire
reef ecosystem.
Despite conservational aims, MPAs concentrate fishing pressure into limited zones of the lagoon,
and catch-size regulations encourage catch of larger-bodied commercial fish stocks in those
spatially limited fishing zones. Observed decrease in parrotfish size and abundance inside fishing
zones compared to MPAs reveal the vulnerability of fishing zones to transitions in lagoon
management, as well as the ensuing size-selective fishing pressure of functionally critical
parrotfishes.
Spatial Dynamics
Site
Results indicate that MPAs support a higher biomass of parrotfish than adjacent fished sites, in
terms of average body size and abundance of fishes (Fig. 3 & 4). The smaller body size of
parrotfish in fished sites suggests that parrotfish are indeed sensitive to fishing pressure. Despite
differences in size between sites, however, it is important to note that the difference was minimal
(1.3 cm ± 4 cm). This suggests that parrotfish island-wide may be responding to influences other
than fishing pressure. Human-derived factors such as tourism, boat traffic, and pollution, as well
as environmental factors such as ocean current, wave action, or natural disturbance are potential
additional factors influencing size. While MPA and fished pairs were chosen based on proximity
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and similarity of geomorphological conditions, some MPAs were exposed to a much stronger
current than their fished pairs (such was the case at Temae, P1 & F1), and other MPAs were
exposed to heavier boat traffic and tourist activity than their fished pairs (such was the case at
Tiahura Motu and its fished pair, P4 & F3).
The minimal difference in average body size between sites may also be due to a lack of data on
parrotfish range in Mo’orea. Parrotfish range is extremely variable, differing according to life
history stage, species, depth, latitude, and lunar phase (Howard, et al., 2013). While the spatial
proximity between fished and MPA pairs were determined based on the home range of parrotfish
reported in Howard’s (2013) study, it is possible that individual home ranges ‘spilled over’
between pairs. In addition, terminal phase individuals (large bodied) have larger home ranges
than initial phase individuals (Howard, et al., 2013); therefore, the same large-bodied parrotfish
may have been observed in both the MPA site and its fished pair. If this is the case, it can be
suggested that parrotfish are vulnerable to size-selective fishing regardless of which site they
were observed in during this study. Subsequently, this proposes that MPAs in Mo’orea may not
have as great of a “reserve effect” on parrotfish abundance and size as they have been found to
have with other fish species in different locations of the world (Polunin and Roberts, 1993;
Walker and Robinson, 2009; Starr et al., 2015). While managers may use MPAs as tools to
regulate fishing pressure and maintain biodiversity, this study confirms that MPAs are
redistributing fishing pressure into concentrated zones of the lagoon. Overexploitation of largebodied parrotfish in those zones is inadvertently leading to populations dominated by smallerbodied parrotfish throughout the lagoon.
The short timescale of this study is an additional factor to consider when comparing the effects
of the PGEM on parrotfish size between sites. For instance, MPA reserve benefits might be slow
to accumulate given the relatively recent establishment of MPAs. Previous studies suggest that
20 years or more may be needed to detect significant changes in response variables that are due
to the establishment of MPAs (Starr et al., 2015). Factors such as short-term environmental
variability and the high spatial and temporal variability of fish recruitment patterns could
influence the impression of how MPAs are working, making short-term ecosystem monitoring
inconclusive and unrepresentative of greater ecological patterns (Starr et al., 2015). Given the
high frequency of environmental disturbances in Mo’orea (Lamy et al., 2015; Adam et al., 2011),
long-term monitoring is needed to identify greater patterns of ecosystem responses to humanderived disturbances such as size-selective fishing.
The negligible difference between average parrotfish size in MPA and fished sites has important
consequences for the future trajectory of Mo’orea’s reef ecosystem. The decline in grazing
capacity of fish in both managed areas and fished areas suggests reduced resilience of reefs
throughout the lagoon, including reefs exposed to fishing pressure and reefs absent of fishing
pressure. Consequences of an island-wide decrease in parrotfish size may include a decreased
response rate and functional aptitude of populations to graze the reef following natural
disturbance-mediated shifts to macroalgal dominance (Barba, 2010). This, in turn, may entail
unrecoverable phase shifts of the lagoon ecosystem to algal domination (Roff and Mumby,
2012; Bonaldo and Bellwood, 2008; Hoey and Bellwood, 2008; Roff et al., 2011; Wilder, 2003;
Hay, 1984). Island-wide declines in functional diversity may also denote a decreased gene pool
of large-bodied parrotfish (Pope and Macer, 1996). Implications of this for future parrotfish
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populations could include: reduced growth, shorter life span, earlier maturation, or earlier sex
reversal, as found in a similar study analyzing the effects of fishing pressure on two parrotfish
species (C. sordidus and S. psittacus) (Barba, 2010). Loss of genetic diversity (Smith, Francis &
McVeagh, 1991) and change in assemblage structure (Russ and Alcala, 1989) are further
consequences of increased fishing pressure.
Location
Parrotfish size varied with location. Average size was different between each location, being
greatest at Tiahura (29 cm) and smallest at Pihaena (24 cm). Tiahura was unusual because its
paired MPA and fishing site differed greatly in terms of human presence. The MPA site was
situated next to Tiahura Motu, a motu frequently visited by tourists and in close proximity to
picnic tables and a restaurant (Fig. 1). The fished site was barren of tourists and fishermen on
both occasions surveyed; however, despite this, fish were still large and plenty in that site. Fish
size is therefore naturally larger in this location, possibly due to the increased availability of food
from nearby picnicking activity. The smaller size of parrotfish in Pihaena may be explained by
both sites’ proximity to channel markers and corresponding boat traffic. Regardless of these
anthropogenic influences, however, Mo’orea’s lagoon has been observed to be naturally
heterogeneous throughout (Lison de Loma et al., 2008; Lamy et al., 2015; Adam et al., 2011).
Similarly to this study, Lamy (2015) found a large variation in the functional responses of
herbivorous fish across the western and northeastern reefs of Mo’orea, despite homogenization
of the entire lagoon habitat toward reduced coral cover and complexity. This spatial
heterogeneity of coral-reef fish morphology and functional diversity provides further evidence
that species might differ with respect to other factors that influence their responses, such as
environmental characteristics. This could explain the variation in parrotfish size between
locations around Mo’orea, especially as ocean current, wave exposure, boat traffic, and tourism
activities vary island-wide.
Habitat
In addition to site and location, this study also found differences in parrotfish size in two
different reef habitats within the lagoon. In almost every site, parrotfish size and abundance were
greater in the back reef than in the fringing reef (Fig. 7). Body size was especially larger in backreef habitats in fished sites compared to that in fringing reef habitats in fished sites (Fig. 7).
Combined, these data suggest that the fringing reef may be more vulnerable to size-selective
fishing than the back reef. Interactions with local fishermen support this claim, as the majority of
fishermen are recreational fishermen, fish before 7 am and after 7 pm, and use spearfishing as
their main method (Fig. 9) (Rice, 2016, Personal observation). Given that most recreational
fishermen do not use boats (Leenhardt et al., 2016), and the preferred times to fish are in periods
of limited sunlight, responses suggest that most fishermen fish just off shore in the fringing reef,
rather than the distant back reef. Furthermore, the reserve effect of MPAs has been found to be
greatest towards the back reef of the lagoon, and smallest within the fringing reef (Lison de
Loma et al., 2008). Together with my results, this implies that, regardless of site, parrotfish in the
fringing reef are more vulnerable to size-selective fishing pressure that parrotfish in the back
reef.
The present study found variation in parrotfish size on many spatial scales. Such variation
suggests the differing vulnerabilities of parrotfish to fishing pressure according to location and
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reef habitat. While Lamy (2015) asserts that differing spatial responses of herbivorous fishes to
natural disturbance may provide Mo’orea’s reef ecosystem with greater resilience, differing
spatial responses as a result of human-derived disturbances such as fishing may not provide the
same ecosystem benefits. Unlike environmental disturbances (such as cyclones and bleaching
events), anthropogenic disturbances are not part of the regime under which coral-reef ecosystems
have evolved. Thus, differing spatial responses of parrotfish size to fishing pressure in a nonenvironmentally disturbed state may be either a reflection of the variability of fishing pressure at
each location, or the variability of vulnerabilities of parrotfish throughout different parts of the
lagoon. Regardless, we cannot assume Mo’orea’s reefs will remain resilient in the face of
disturbance as they have in the past, especially when considering the mounting consequences of
an ever-increasing human population on ecosystems such as Mo’orea’s lagoon.
Temporal Dynamics
Lunar occasion
Over the short temporal scale of this study, fish abundance at any one site and time is highly
variable and unreliable as an absolute measure of herbivore pressure (Starr et al., 2015). The
current study observed greater average body sizes during the full moon in comparison with the
new moon, and no differences in fish abundance between lunar occasions. Previous studies have
found that fish abundance and behavior differ according to moon phase (Vinson, 2014);
however, finding a difference in average fish-body size between lunar occasions was an
unexpected result. This finding suggests that either different parrotfish were observed at each site
during the two survey occasions, or that smaller parrotfish were simply not observed due to
cryptic behavior during the full moon (Galzin, 1987).
Mo’orea’s fishing population
Mo’orea’s population has increased at an unsustainable rate in recent decades. From 2007 to
2012 alone, Mo’orea’s population increased 6.33% (ISPF, 2015) (Fig. 10). In addition, estimates
of fishing density in 2007 revealed 77 fishermen per km2 (Brenier, 2009). If this calculated
fishing pressure is accurate, it is quite high considering that five fishermen per km2 is the upper
limit at which coral reef resources can be safely exploited (McClanahan et al., 2002). Assuming
population and fishing density are proportional, this indicates that fishing density in 2012 was 82
fishers per km2. Furthermore, assuming population growth rate hasn’t increased since 2012, the
current fishing density in 2016 may be as high as 86 fishers per km2; however, as population
growth appears to be increasing exponentially (Fig. 10), fishing density today is most likely even
higher.
The implications of this unprecedented increase in population are noteworthy, to say the least.
While consequences are apparent on land (i.e. pollution, hillside construction, crowded public
spaces), the most threatening costs are hidden beneath the surface of the lagoon. Given that
fishermen attain higher economic gains from larger fish and understanding the effect of the
PGEM’s regulation on minimum catch size, an increased population means increased targeting
pressure on larger parrotfish. For example, roadside fish size evaluations from Madi Moussa’s
(2010) study in 2007 found average parrotfish catch size was 27 cm ± 2 cm, compared to a
minimum legal catch size of 25 cm. In addition, as lagoon fishing exploits only a few species,
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with only five to six species representing more than 80% of total sales (Madi Moussa, 2010),
parrotfish in the lagoon are especially vulnerable to size-selective fishing pressure.
To attain an understanding of responses of the lagoon ecosystem to increases in demand for
larger parrotfish, this study took a socio-ecological approach using a survey technique referred to
as “participatory monitoring” (Leenhardt et al., 2016) and included the local population in the
quest for ecological information, both qualitative and quantitative. In the context of ecological
awareness, such anecdotal monitoring has its value, but also its limits. In all cases, participatory
monitoring presupposes that research provides itself with the means of its supervision, betting in
some way on its instructive and administrative efficiency. Although the information collected
was quantitative, it involved substantial uncertainty because it relied on the long-term memory of
the person interviewed and his or her ability to convert an image or a memory into a physical
size (Gilbert, 2006). Responses from surveys are thus considered qualitative.
Estimates of parrotfish body size from the beginning of a fisherman’s career revealed the
vulnerability of parrotfish to varying levels of demand over a timescale of 60 years (Fig. 8).
Given that each interview was independent from the next, and observations included a wide
demographic of fishermen, the mutual decline in parrotfish size from 1956 to 2013 reputes
fishermen knowledge, and also reinforces the perceived decline in parrotfish size over time.
Additionally, when comparing size estimates from 1956 to 2013 to population size over the same
time scale, a weak inverse relationship between estimated fish size and human population size is
evident. Thus, estimating observable ecological variables through participatory monitoring—
especially in a rural community deeply connected with their natural environment (Budd-Falen,
1995; Jentoft, 1999)— can contribute to the collective understanding of ecological change over
time, especially in the absence of scientific data from earlier time periods.
Application to future marine management strategy
Civic engagement ensures environmental and economic sustainability in rural communities
(Budd-Falen, 1995; Jentoft, 1999), and the intergenerational environmental knowledge of local
resource users is comprehensive and relevant to modern conservation objectives. This case study
in Mo’orea raises questions about the assumed connections between local control, public
participation, and successful conservation results. Especially in Mo’orea’s lagoon where
underwater resources and ecological processes are not sedentary, visible, or easily quantified,
there was considerable debate between differing stakeholders including locals, the state, and
scientists over indicators of lagoon health, patterns of fish reproduction and larval transport, the
dynamics of land-based pollution effluents, and the location and importance of different lagoon
uses and meanings (Walker, 2001). While the government and biologists cited “scientific”
studies and spatial data to support the creation of the PGEM, Mo’orea’s stakeholders likewise
asserted their own knowledge of the lagoon by describing traditional lagoon management and
fishing laws, reciting Maohi legends about Mo’orea and its lagoon, and explicating their lifelong, daily interactions with the fish, coral reefs, sharks, and other organisms of Mo’orea’s
lagoon (Walker, 2001). Walker (2001) found that many of Mo’orea’s fishermen keep detailed
diaries of fishing information, which have been passed down for generations. These diaries
include daily explanations of where different species of fish are found in the lagoon, based on a
variety of indicators such as currents, winds, lunar cycle, and seasons. Older fishermen, in
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particular, claim knowledge of their home lagoon areas at the scale of individual coral heads, and
they are able to explain precisely where, at what time, and on what day one can go to catch a
particular species of fish (Walker, 2001). Despite fishermen’s comprehensive and relevant
environmental knowledge of their lagoon, the government alienated locals from the deliberation
process through the privileged use of GIS decision-making, a resource not accessible to the
majority of Mo’orea’s local population (Walker, 2001). As a result, state-mandated MPAs
spurred significant political struggles and prompted resistance among locals unlike any previous
resource regulation in French Polynesia (Yousing, 2016; Rey, 2016; Bambridge, 2016; Aubanel
et al., 2013; Walker and Robinson, 2009; Walker, 2001). Consequently, and, as this current study
suggests, absence of local cooperation might ultimately render MPA management plans
unsustainable. The mapping of MPAs in Mo’orea highlighted discrepencies between
policymaker recommendations and fishermen ecological knowledge, conflicts over access to
lagoon space and resources, and disagreements over evolving forms of lagoon conservation
(Yousing, 2016; Rey, 2016; Walker, 2001). Westerners, developers, and tourists were handed
control of large zones of the lagoon, promoting tourist activities in parts of the lagoon that
residents previously relied on for sustenance (Yousing, 2016; Rey, 2016; Walker, 2001).
Accordingly, alienated stakeholders formed politicized local associations to defend their own
livelihoods and sovereignty, and display their opposition to government interference into lagoon
management, as well as foreign exploitation of the lagoon (Bambridge, 2016; Rey, 2016;
Walker, 2001).
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The effects of fishing on marine ecosystem structure and processes are significant and complex.
Results from this study highlight the inverse relationship between size-selective fishing
intensity and the average size of the herbivorous reef-fish family Scaridae greatly targeted by
Mo’orea’s fishing population. Ecological relationships and questions relevant to the marine
environment must be studied on many spatial and temporal scales, as the marine environment
can be incredibly variable according to location, habitat, and moon phase, as this study revealed.
The use of bio-indicators such as herbivorous fish size can enhance our understanding of fishing
effects throughout space and time. Assessing both the spatial and temporal variations in
Several of these local associations support a movement to revert to a traditional management
system that many islands in French Polynesia previously used, and some islands such as Rapa
and Maiao still use (Agence des aires marines protégées, 2012). Referred to as “Rahui,” this
traditional style of management accounts for local understanding of, and relationship with,
natural resources, embracing holistic and rational modes of enforcement and avoiding
overregulation (Bambridge, 2016). The ocean and the reef ecosystem have survived centuries of
disturbance without human interference. However, as indicated by this study, human-centered
management strategy, despite well-intentioned environmental objectives, shows detrimental
effects on the reef ecosystem. Locals that have been fishing on Mo’orea their whole lives
understand the consequences of a poorly managed reef (Yousing, 2016). Managing land should
be in the best interest of the natural environment and the local stakeholders, not foreign
developers. If we want the reef to remain resilient in the face of increasing demand of its
resources, we must equally integrate local stakeholders, and consider the ecological dynamics
that sustain a reef, such as fish life history, reproductive stage, and especially, ecosystem
function, as Rahui considers.
Conclusions
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parrotfish and other herbivorous species’ composition is important to comprehensively explore
the effects of size-selective fishing pressure, and thus the vulnerability of the coral-reef
ecosystem to reductions in resilience. Enforcements to capture parrotfish characteristic of the
highest grazing activity, in a small-scale fishery with limited fish supply and an increasing
fishing population may hinder the grazing capacity of parrotfish further, and make phase shifts to
a macroalgal-dominated state more likely. Size-selective fishing of a species keystone to the reef
ecosystem is a result of population-based marine management strategy, and the resulting
vulnerability of the reef ecosystem has only just gained recognition. More evidence is needed to
determine a scientific basis for a change from population-based management to ecosystem-based
management for the vulnerable marine ecosystem in Mo’orea and elsewhere. Extensive time
series data on the responses of various, diverse ecosystems to anthropogenic transitions such as
population increase and management strategy will create a record for future managers to consult
when strategizing sustainable solutions for preserving the earth’s natural resources.
Acknowledgements
I would like to thank all of my Professors, Patrick O’Grady, Jonathon Stillman, Justin Brashares,
Cindy Looy, and Ivo D. for all of the help and time that they put into developing my project and
editing my paper. I would also like to thank the graduate student instructors Natalie StaufferOlsen, Ignacio Escalante, and Eric Armstrong for their endless support and dedication to making
this experience one of a lot of learning, as well as a lot of fun. I would also like to thank Alex
Yokley and Ryan Mullen for always being willing survey buddies, and my family for their
inspiration and support. Additionally, I would like to thank the wonderful Gump Station and
Atitia Center staff, Val, Irma, Jaques, Tony, Frank, and Hinano for sharing their bliss and culture
with us. Finally, I would like to thank all of my amazing classmates who made this experience
truly unforgettable. Maururu roa. #nofermentedfish2k16.
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PeerJ Preprints | https://doi.org/10.7287/peerj.preprints.2657v1 | CC BY 4.0 Open Access | rec: 21 Dec 2016, publ: 21 Dec 2016
Figure 1
Marine Protected Areas (MPAs) defined by the PGEM in Mo’orea’s lagoon (PGEM 2005).
MPAs are represented in black zones. I selected five out of the total eight MPAs defined by
the PGEM (labeled P1, P2, P3, P4, and P5), and I selected four paired fishing zones (labeled
F1, F2, F3, and F5), represented in white zones.
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Figure 2
Histogram of response variable (cm) showing normal data.
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Figure 3
Average parrotfish size (cm) between variables: site (A), location (B), reef habitat (C),
and lunar occasion (D).
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Figure 4
Average parrotfish abundance between variables: site (A), location (B), reef habitat (C),
and lunar occasion (D). Only “Site” was statistically significant.
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Figure 5
Parrotfish size according to geographic location of paired fishing and MPA sites. Error
bars represent 95% confidence intervals.
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Figure 6
Parrotfish abundance according to geographic location of paired fishing and MPA sites.
Error bars represent standard error around the mean.
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Figure 7
Box-plot showing interactions between site (in red and blue), location (z-axis), and
habitat type (x-axis) with fish size (cm) (y-axis).
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Figure 8
Estimates of parrotfish size (cm) over time. Blue dots represent fishermen estimates at
the start of their fishing career (1956-2013). Red dot represents averaged fisherman
estimate of parrotfish size (cm) today (2016).
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Figure 9
Participatory survey responses from 50 fishermen. Y-axes represent frequency of
response per question.
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Figure 10
Mo’orea’s population from 1959 to 2012 as recorded by ISPF (ISPF 2015).
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Table 1(on next page)
Four-way ANOVA with size (cm) as the response variable and site, location, habitat type,
and lunar occasion (“phase”) as the predictor variables.
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Df Sum Sq Mean Sq F value
Pr(>F)
Site
1
277
277.1 22.061 3.19e-06 ***
Loc
4
1608
402.0 31.998 < 2e-16 ***
Hab_Type
1
701
700.6 55.774 2.46e-13 ***
Phase
1
442
441.6 35.153 4.81e-09 ***
Site:Loc
4
397
99.3
7.902 3.13e-06 ***
Site:Hab_Type
1
23
23.3
1.857 0.17336
Loc:Hab_Type
4
729
182.2 14.500 2.23e-11 ***
Site:Phase
1
1
0.5
0.041 0.84012
Loc:Phase
4
551
137.6 10.956 1.28e-08 ***
Hab_Type:Phase
1
217
216.8 17.258 3.67e-05 ***
Site:Loc:Hab_Type
2
242
121.1
9.637 7.45e-05 ***
Site:Loc:Phase
4
725
181.2 14.423 2.56e-11 ***
Site:Hab_Type:Phase
1
101
100.9
8.028 0.00474 **
Loc:Hab_Type:Phase
4
366
91.4
7.277 9.63e-06 ***
Site:Loc:Hab_Type:Phase
1
5
4.9
0.391 0.53192
Residuals
692
8693
12.6
--Signif. codes: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1
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