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.蝠𫚉（Mobulid rays）具有保守的生活史特征，既会被直接捕捞，也会作为兼捕渔获物被捕获。其面临过度捕捞的脆弱性现已得到学界认可，但倘若渔业管理忽视目标物种的栖息地与猎物偏好，以及其他营养级相互作用关系，则可能无法达到预期管理效果。本研究针对菲律宾保和海海域的4种蝠𫚉物种（双吻前口蝠鲼Manta birostris、智利蝠鲼Mobula tarapacana、日本蝠鲼M. japanica、图氏蝠鲼M. thurstoni），通过分析2013-2015年11月至次年5月间上岸的渔业捕捞标本的胃含物，对其摄食生态展开评估。研究发现，该海域的蝠𫚉每年有约6个月的时间会大量捕食磷虾类（euphausiid krill）。本研究未观测到不同蝠𫚉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底眼磷虾（Euphausia diomedeae）：在总计89个胃样本中，有81个（占比91%）检出该物种。其中日本蝠鲼与图氏蝠鲼的胃容物几乎完全由该磷虾组成；智利蝠鲼的胃内除该磷虾外，还包含头足类与鱼类；双吻前口蝠鲼则额外摄食灯笼鱼科（Myctophidae）鱼类与桡足类（copepods）。该磷虾的体型大于其他海域中滤食性板鳃类（elasmobranchs）的猎物，单胃中该磷虾提供的平均能量为61364千卡（标准误±105032千卡，能量范围0~631167千卡）。本研究结果表明，垂直洄游的中层大洋物种（mesopelagic species）可作为生活在贫营养表层水域热带海域的大型滤食性动物的重要食物来源。鉴于蝠𫚉保守的生活史特征，识别出与捕捞活动重叠的共同觅食场域，可为未来渔业作业规划提供科学依据。