Inter-American Tropical Tuna Commission, Bycatch Program, La Jolla, San Diego, CA, United States of America.
AZTI-Tecnalia, Marine Research Division, Pasaia, Spain.
PLoS One. 2019 Aug 7;14(8):e0220854. doi: 10.1371/journal.pone.0220854. eCollection 2019.
In the eastern Pacific Ocean, the tropical tuna purse-seine fishery incidentally captures high numbers of five mobulid bycatch species; all of which are classified as mortalities by the Inter-American Tropical Tuna Commission due to uncertainties in post-release mortality rates. To date, the factors (operational or environmental) leading to the capture of these species by the fishery have not been well studied. Here, we developed Generalized Additive Models for fisheries observer data to analyze the relationships between the presence/absence of Mobula mobular bycatch and oceanographic conditions, the spatial and temporal variability in fishing location, and the set type (associated with dolphins, free-swimming tuna schools or floating objects). Our results suggest that chlorophyll concentration and sea surface height are the most important variables to describe the presence of M. mobular in conjunction with geographic location (latitude and longitude) and set type. Presence of the species was predicted in waters with chlorophyll concentrations between 0.5-1 mg·m-3 and with sea surface height values close to 0; which indicates direct relationships with productive upwelling systems. Seasonally, M. mobular was observed more frequently during December-January and August-September. We also found the highest probability of presence observed in School sets, followed by Dolphin sets. Three areas were observed as important hotspots: the area close to the coastal upwelling of northern Peru, the area west to Islands Colon Archipelago (Galapagos) and the area close to the Costa Rica Dome. This information is crucial to identify the mobulids habitat and hotspots that could be managed and protected under dynamic spatial management measures to reduce the mortality of mobulid rays in the eastern Pacific purse-seine fishery and, hence, ensure the sustainability of the populations of these iconic species.
在东太平洋，热带金枪鱼围网渔业偶然捕获了五种蝠鲼属副渔获物；由于后释放死亡率的不确定性，所有这些物种都被美洲热带金枪鱼委员会归类为死亡。迄今为止，导致这些物种被渔业捕获的因素（操作或环境）尚未得到很好的研究。在这里，我们为渔业观察员数据开发了广义加性模型，以分析 Mobula mobular 副渔获物的存在/不存在与海洋条件、捕捞位置的时空变化以及设置类型（与海豚、自由游动的金枪鱼群或漂浮物相关）之间的关系。我们的结果表明，叶绿素浓度和海面高度是描述 M. mobular 存在的最重要变量，与地理位置（纬度和经度）和设置类型相结合。在叶绿素浓度在 0.5-1 mg·m-3 之间且海面高度值接近 0 的水域中预测到了该物种的存在；这表明与生产力上升流系统有直接关系。季节性地，M. mobular 在 12 月至 1 月和 8 月至 9 月期间观察到的频率更高。我们还发现，在 School sets 中观察到的存在概率最高，其次是 Dolphin sets。观察到三个重要的热点区域：靠近秘鲁北部沿海上升流的区域、群岛科隆群岛（加拉帕戈斯群岛）以西的区域以及靠近哥斯达黎加圆顶的区域。这些信息对于确定蝠鲼属的栖息地和热点区域至关重要，可以根据动态空间管理措施进行管理和保护，以减少东太平洋金枪鱼围网渔业中蝠鲼属射线的死亡率，并确保这些标志性物种的种群可持续性。
