Best Management Strategies for Sustainable Giant Clam Fishery in French Polynesia Islands: Answers from a Spatial Modeling Approach

Type Article
Date 2013-05
Language English
Author(s) Van Wynsberge Simon1, Andrefouet Serge1, Gilbert Antoine2, Stein Arsene3, Remoissenet Georges3
Affiliation(s) 1 : Inst Rech Dev, UR CoReUs, Noumea, New Caledonia.
2 : Ginger Soproner, Noumea, New Caledonia.
3 : Direct Ressources Marines, Papeete, Fare Ute, France.
Source Plos One (1932-6203) (Public Library Science), 2013-05 , Vol. 8 , N. 5 , P. e64641 (15p.)
DOI 10.1371/journal.pone.0064641
WOS© Times Cited 17

The giant clam Tridacna maxima has been largely overexploited in many tropical regions over the past decades, and was therefore listed in appendix II of the Convention of International Trade in Endangered Species (CITES) in 1985. In French Polynesia, several atolls and islands harbor the world's highest stocks of giant clams in very shallow and accessible areas, which are therefore highly vulnerable to fishing pressure. The local fishery authority (i.e., Direction des Resources Marines or "DRM") implemented several management schemes in 2002 to control and regulate fishing pressure. However, for further decisions DRM was missing a sensitivity analysis on the effectiveness of the possible management actions. Here, we report on the use of a deterministic Viable Population Analysis (VPA) and spatially-explicit age-based population model that simulated the 30-year trajectory of a Tridacna maxima stock under different management approaches. Specifically, given various scenarios of intra-island larval dispersal, we tested which of No-take-Areas (NTAs), rotational closures, size limits, quotas, and restocking schemes would lead to the highest future stocks in Tubuai and Raivavae, two exploited islands of the Austral archipelago. For both islands, stock abundances were estimated in 2004/2010 and 2005/2010 respectively, and natural mortalities were assessed previously only in Tubuai. When compared to field data, the model successfully predicted the 2010 stocks for Tubuai, but proved to be less reliable for Raivavae, where natural mortality rates may well be different from those on Tubuai. For Tubuai, the spatial model suggested that reducing fishing effort (through fixed quotas) and banning fishing below the 12 cm size limit (as currently implemented) were the most effective management actions to sustain T. maxima populations into the future. Implementing NTAs was of poor effectiveness. NTAs increased giant clam stock inside the protected area, but also increased overfishing in the neighboring areas, and were ineffective overall.

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Figure S1. Range of values used for Tubuai and for each component of the Leslie Matrix used in the model, without any management action. 56 KB Open access
Figure S2. Projection of future stocks for Tubuai in tons of spawning biomass estimated by the model under various scenarios of management. 272 KB Open access
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