Commercial Coral Reef Fish Community Structure along an Island Gradient of Contrasting Habitat and Fishing Pressure in the Society Archipelago (French Polynesia) Thierry LISON DE LOMA CRIOBE Centre de Recherches Insulaires Observatoire de l'environnement UMS 2978 CNRS - EPHE thierry.lison@mail.pf
- Representativity of Moorea? - Homogeneity of fore reef in Moorea? - Impact of fishing on fish communities in Moorea? - Implications for long-term monitoring?
Dynamics and demographics of commercial fish communities rely on: - geomorphology and habitat structure - fishing pressure - larval recruitment - predator-prey relationships = > Rationale Respective effects of these two factors on population descriptors (density, biomass, size)? Sampling technique: fixed point UVC (surface: 150 m 2 ) Sampling on on fore reef (10 < D < 15 15 m) m)
UVC - stationary : - species - abundance - size (FL) - habitat description Site 18 - Moorea Site 14 - Raiatea
Commercial species in 19 families QuickTime et un décompresseur Serranidae (Groupers) Scaridae (Parrofishes) Carangidae (Jacks) QuickTime et un décompresseur Lutjanidae (Snappers) Priacanthidae (Big-eyes) Sphyraenidae(Barracudas) Unfished family Acanthuridae (Surgeonfishes) Holocentridae (Soldier- Squirrelfishes) Chaetodontidae (Butterflyfishes)
Study sites Maupiti Moorea Raiatea Tahiti 20 sites, 60 UVC around each island => 80 sites, 240 UVC
Density and biomass (ind.100 m -2 ) (g.m -2 ) 110 species, 29 29967 individuals Total fish community Island Density (± SD) Biomass (± SD) Moorea 95.0 ± 30.8 274 ± 222 Raiatea 88.1 ± 47.9 340 ± 247 Tahiti 81.3 ± 34.2 262 ± 199 Maupiti 66.8 ± 53.5 289 ± 212 Commercial fish community Island Density (± SD) Biomass (± SD) Raiatea 77.7 ± 48.8 335 ± 247 Moorea 76.7 ± 28.8 267 ± 220 Tahiti 68.2 ± 32.9 257 ± 199 Maupiti 58.4 ± 52.5 281 ± 212
- Good correlation between massive corals,, fore reef steepness, rugosity, habitability and commercial communities. - Good correlation between branching corals and butteflyfish communities. - Lack of correlation between commercial species and unfished species Principal Component Analysis: Canonical correspondence Analysis: - 20 % of total variation explained by habitat. => what proportion of the observed variations is due to fishing?
Density, biomass and fishing pressure in the selected islands Linear regression: biomass / fishing pressure Linear regression: density / fishing pressure
Size distribution of high commercial interest species in the four selected islands Absence of big sized individuals in Maupiti and Moorea, quasi-absence absence in Tahiti. Number of individuals in bigger size classes ( ( 40 cm) higher in Raiatea and Maupiti.
Mean size of 10 selected species in the four studied islands Mean fish size bigger in Raiatea and Maupiti than in Moorea and Tahiti
Biomass of trophic groups in the four selected islands Micro herbivores generally dominant. Relative dominance of piscivores and macro invertivores in Raiatea, and of macro herbivores and zooplanktivores in Maupiti
Trophic groups characterizing the four different islands: Correspondance Analysis Tahiti-Moorea -alg -alg Pisc/M-inv Pisc/M-inv M/ -alg M/ -alg M/ -inv M/ -inv M-inv M-inv -alg/ -inv -alg/ -inv Pisc Pisc Raiatea Raiatea Axe 1 (21 %) Axe 1 (21 %) M-alg M-alg -alg/zpk -alg/zpk Pisc/Zpk Pisc/Zpk Maupiti Maupiti Zpk Zpk Axe 2 (18 %) Axe 2 (18 %) Contribution relative forte : sur axe 1 Contribution relative forte : sur sur axe axe 2 1 sur axe 2 Axis 1 : Raiatea/Piscivores Piscivores-Macroinvertivores opposed to Tahiti-Moorea and Maupiti. Axis 2 : differenciation Tahiti-Moorea Moorea/MicroherbivoresMicroherbivores and Maupiti/Zooplanktivores Zooplanktivores.
Size and trophic groups distribution in the Society Islands Potential causes : - direct effect of fishing -Species transdominance through predator- prey interactions
CONCLUSIONS - Significant decline in density and biomass of commercial coral reef fishes in the Leeward Islands of Tahiti and Moorea. Maximum figures in Raiatea. - Decrease in mean size of common species in the Leeward Islands, and drastic reduction of big sized individuals. - Change in trophic structure in Maupiti (relative dominance of macro herbivores et zooplanconophages), in Moorea and Tahiti (dominance of micro herbivores). Relative dominance of piscivores in Raiatea. - Significant negative correlations between fishing pressure descriptors and density and biomass.
IMPLICATIONS AND PERSPECTIVES - Fore reef fish communities are very different between islands and sites: long term monitoring needed at the regional scale. - Conservation. - Study of commercial fish communities in deeper habitats and lagoons: estimation of stocks for sustainable fisheries, connectivity between different reef geomorphological units. - A better estimation of fishing efforts needed. - Acquire more knowledge on life history traits and recruitment patterns of target species: prediction of density and biomass decrease rates, resilience of commercial fishes.
Commercial Coral Reef Fish Community Structure along an Island Gradient of Contrasting Habitat and Fishing Pressure in the Society Archipelago (French Polynesia) Thierry LISON DE LOMA CRIOBE Centre de Recherches Insulaires Observatoire de l'environnement UMS 2978 CNRS - EPHE thierry.lison@mail.pf