UR-CoRéUs, Institut de Recherche pour le Développement, Nouméa, New-Caledonia.
PLoS One. 2013 May 28;8(5):e64641. doi: 10.1371/journal.pone.0064641. Print 2013.
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.
在过去几十年中，巨型蛤 Tridacna maxima 在许多热带地区遭到了过度捕捞，因此于 1985 年被列入《濒危野生动植物种国际贸易公约》（CITES）附录 II。在法属波利尼西亚，几个环礁和岛屿拥有世界上最高的巨型蛤资源，这些蛤位于非常浅且易于到达的地区，因此极易受到捕捞压力的影响。当地渔业管理局（即海洋资源管理局或“DRM”）于 2002 年实施了多项管理计划，以控制和调节捕捞压力。然而，DRM 还需要对可能的管理措施的有效性进行敏感性分析，以便做出进一步的决策。在这里，我们报告了使用确定性可行种群分析（VPA）和基于年龄的空间显式种群模型来模拟 Tubuai 和 Raivavae 两个已开发岛屿的 30 年 Tridacna maxima 种群轨迹。具体来说，鉴于岛内幼虫扩散的各种情景，我们测试了在哪些情况下建立禁捕区（NTAs）、轮捕、尺寸限制、配额和补放计划可以在 Tubuai 和 Raivavae 这两个澳大利亚群岛的已开发岛屿上带来最高的未来种群。在这两个岛屿上，分别于 2004/2010 年和 2005/2010 年估计了种群数量，之前仅在 Tubuai 评估了自然死亡率。与实地数据相比，该模型成功预测了 2010 年 Tubuai 的种群数量，但对于 Raivavae 的预测结果却不太可靠，因为那里的自然死亡率可能与 Tubuai 不同。对于 Tubuai，空间模型表明，通过固定配额减少捕捞努力和禁止捕捞 12 厘米以下的尺寸限制（如目前实施的那样）是维持 T. maxima 种群未来的最有效管理措施。建立禁捕区的效果不佳。禁捕区增加了保护区内的巨型蛤数量，但也增加了邻近地区的过度捕捞，总体上效果不佳。
