Data from: Mobulid rays feed on euphausiids in the Bohol Sea

Mobulid rays have a conservative life history and are caught in direct fisheries and as bycatch. Their subsequent vulnerability to overexploitation has recently been recognised, but fisheries management can be ineffective if it ignores habitat and prey preferences and other trophic interactions of the target species. Here, we assessed the feeding ecology of four mobulids (Manta birostris, Mobula tarapacana, M. japanica, M. thurstoni) in the Bohol Sea, Philippines, using stomach contents analysis of fisheries specimens landed between November–May in 2013–2015. We show that the mobulids feed heavily on euphausiid krill while they are in the area for ~6 months of the year. We found almost no trophic separation among the mobulid species, with Euphausia diomedeae as the major prey item for all species, recorded in 81 of 89 total stomachs (91%). Mobula japanica and M. thurstoni almost exclusively had this krill in their stomach, while M. tarapacana had a squid and fish and M. birostris had myctophid fishes and copepods in their stomachs in addition to E. diomedeae. This krill was larger than prey for other planktivorous elasmobranchs elsewhere and contributed a mean of 61,364 Kcal per stomach (±105,032 Kcal s.e., range = 0–631,167 Kcal). Our results show that vertically migrating mesopelagic species can be an important food resource for large filter feeders living in tropical seas with oligotrophic surface waters. Given the conservative life history of mobulid rays, the identification of common foraging grounds that overlap with fishing activity could be used to inform future fishing effort.

蝠鲼科鳐类（Mobulid rays）具有保守的生活史特征，既会被直接渔业捕捞，也会作为兼捕渔获物被捕获。这类生物对过度开发的脆弱性近来已得到学界确认，但倘若渔业管理忽视目标物种的栖息地偏好、猎物选择及其他营养级相互作用，往往难以达到预期管理效果。本研究以菲律宾保和海的4种蝠鲼科鳐类为研究对象，包括双吻前口蝠鲼（Manta birostris）、短尾蝠鲼（Mobula tarapacana）、日本蝠鲼（M. japanica）与芒氏蝠鲼（M. thurstoni），通过分析2013-2015年11月至次年5月间上岸的渔业捕获个体的胃含物，评估了其摄食生态学特征。研究结果显示，该区域的蝠鲼科鳐类在每年约6个月的居留周期内，主要以磷虾（euphausiid krill）为食。我们未发现不同蝠鲼物种间存在显著的营养生态位分化：所有物种的核心猎物均为迪奥梅德磷虾（Euphausia diomedeae），在总计89个胃样本中，有81个（占比91%）检出该物种。其中日本蝠鲼与芒氏蝠鲼的胃内容物几乎仅包含该种磷虾；短尾蝠鲼的胃中除迪奥梅德磷虾外，还检出了头足类与鱼类；双吻前口蝠鲼则额外检出了灯笼鱼科鱼类（myctophid fishes）与桡足类（copepods）。该磷虾的体型大于其他区域滤食性板鳃类（elasmobranchs）的猎物，单胃平均能量摄入达61364千卡（标准误±105032千卡，范围0~631167千卡）。本研究结果表明，垂直洄游的中层大洋物种（mesopelagic species）可作为热带寡营养表层水域（oligotrophic surface waters）大型滤食性动物的重要食物资源。鉴于蝠鲼科鳐类保守的生活史特征，识别出与渔业活动重叠的共同摄食栖息地，可为未来渔业作业调控提供科学参考依据。