Dominique Pelletier

Oceanic survival and movements of wild and captive-reared immature green turtles (Chelonia mydas) in the Indian Ocean

The ability of captive-reared turtles to survive in the wild is not precisely known, nor are movements of immature turtles in the open ocean. To provide information on these issues, a satellite tracking experiment was conducted in the western Indian Ocean to monitor oceanic movements of immature green turtles. Two wild turtles and four captive-reared individuals were tracked. The latter had been displaced after birth from nesting sites to a distant rearing site. Wild turtles survived after release, but did not move far away from release site. We hypothesize that this resident behaviour may be explained by stage-specific habitat requirements. Captive-reared turtles survived after release and migrated over thousands of kilometres. Among these, the oldest immature turtles retrieved the foraging sites of their native population, with movement patterns similar to those displayed by adults. Observed movements may be linked to hydrographic conditions such as general oceanic circulation, sea temperature and thermal fronts.

Spearfishing Regulation Benefits Artisanal Fisheries: The ReGS Indicator and Its Application to a Multiple-Use Mediterranean Marine Protected Area

The development of fishing efficiency coupled with an increase of fishing effort led to the overexploitation of numerous natural marine resources. In addition to this commercial pressure, the impact of recreational activities on fish assemblages remains barely known. Here we examined the impact of spearfishing limitation on resources in a marine protected area (MPA) and the benefit it provides for the local artisanal fishery through the use of a novel indicator. We analysed trends in the fish assemblage composition using artisanal fisheries data collected in the Bonifacio Strait Natural Reserve (BSNR), a Mediterranean MPA where the spearfishing activity has been forbidden over 15% of its area. Fish species were pooled into three response groups according to their target level by spearfishing. We developed the new flexible ReGS indicator reflecting shifts in species assemblages according to the relative abundance of each response group facing external pressure. The catch per unit effort (CPUE) increased by ca. 60% in the BSNR between 2000 and 2007, while the MPA was established in 1999. The gain of CPUE strongly depended on the considered response group: for the highly targeted group, the CPUE doubled while the CPUE of the untargeted group increased by only 15.5%. The ReGS value significantly increased from 0.31 to 0.45 (on a scale between 0 and 1) in the general perimeter of this MPA while it has reached a threshold of 0.43, considered as a reference point, in the area protected from spearfishing since 1982. Our results demonstrated that limiting recreational fishing by appropriate zoning in multiple-use MPAs represents a real benefit for artisanal fisheries. More generally we showed how our new indicator may reveal a wide range of impacts on coastal ecosystems such as global change or habitat degradation.

Complementarity of Rotating Video and Underwater Visual Census for Assessing Species Richness, Frequency and Density of Reef Fish on Coral Reef Slopes

Estimating diversity and abundance of fish species is fundamental for understanding community structure and dynamics of coral reefs. When designing a sampling protocol, one crucial step is the choice of the most suitable sampling technique which is a compromise between the questions addressed, the available means and the precision required. The objective of this study is to compare the ability to sample reef fish communities at the same locations using two techniques based on the same stationary point count method: one using Underwater Visual Census (UVC) and the other rotating video (STAVIRO). UVC and STAVIRO observations were carried out on the exact same 26 points on the reef slope of an intermediate reef and the associated inner barrier reefs. STAVIRO systems were always deployed 30 min to 1 hour after UVC and set exactly at the same place. Our study shows that; (i) fish community observations by UVC and STAVIRO differed significantly; (ii) species richness and density of large species were not significantly different between techniques; (iii) species richness and density of small species were higher for UVC; (iv) density of fished species was higher for STAVIRO and (v) only UVC detected significant differences in fish assemblage structure across reef type at the spatial scale studied. We recommend that the two techniques should be used in a complementary way to survey a large area within a short period of time. UVC may census reef fish within complex habitats or in very shallow areas such as reef flat whereas STAVIRO would enable carrying out a large number of stations focused on large and diver-averse species, particularly in the areas not covered by UVC due to time and depth constraints. This methodology would considerably increase the spatial coverage and replication level of fish monitoring surveys.

Decadal increase in the number of recreational users is concentrated in no-take marine reserves

In coastal areas, demographic increase is likely to result in greater numbers of recreational users, with potential consequences on marine biodiversity. These effects may also occur within Marine Protected Areas (MPAs), which are popular with recreational users. Our analysis builds on data collected over a ten-year period during three year-round surveys to appraise changes in recreational boating activities in coral ecosystems. Results show that the number of boaters has greatly increased, particularly so within MPAs during weekends and the warm season, when peaks in boat numbers have become more frequent. We also observed that the number of anchored boats has increased over the period. These changes may be resulting in biophysical impacts that could be detrimental to conservation objectives in MPAs. This steady increase over time may cause changes in the spatial and temporal distribution of users and in their practices, thus highlighting the importance of monitoring recreational activities.

Disentangling the Effects of Habitat and Protection on Coral Reef Fish Communities in Long-Established Marine Reserves

Marine Protected Areas (MPA) play a central role in policies for the conservation of coastal ecosystems and resources. One of the current challenges of monitoring the effectiveness of MPAs at protecting fish assemblages is distinguishing between the influence of habitat, protection effects and anthropogenic activities. We used strongly spatially-replicated data to investigate these effects within an area comprising two no-take long-established marine reserves. Data were obtained from remote underwater video collected across all habitats in the study area. First, each station was assigned to a habitat based on a multivariate typology of biotic and abiotic cover. A number of metrics including fish abundances, assemblage composition and trophic structure were then modeled as a function of habitat and protection status. We showed that protection effects may be easily detected from a number of metrics involving fished species, but for other metrics, effect detection requires that habitat is explicitly taken into account.

Evaluating Management Scenarios for Fished Resources of the New Caledonian Lagoon Using a Spatially-Explicit Model

In the New Caledonian lagoon, fish populations live in a highly-fragmented habitat and seascape, and many are exploited by commercial, recreational and subsistence fishers. Although fishing has been increasing over decades, fisheries sustainability has not been assessed. We used the ISIS-Fish tool to build a spatially-explicit dynamic model for two major fish resources: spangled emperor and coral trout. The model was constructed and parameterized from many existing data habitat, fish populations, and fishing pressures. After calibration, it was used to simulate the outcomes of several management scenarios including MPA, size limitation, and increase in commercial fisher number. Results showed that depending on the species, an MPA could result in a significant resource increase within its boundaries. Size limitation highly reduced line fishing catches, but its benefits depended on the survival rate of released fish. Increasing the number of commercial fishers significantly affected spangled emperor but not coral trout.