Cookiecutter sharks are pelagic ectoparasites that feed on pieces of flesh from large marine animals. Knowledge on these sharks is still rather scant, with the few existing works successfully using bites found on prey to reveal ecological patterns. This study aims to identify cookiecutter shark bite patterns on pelagic fishes in aggregated schools to gain an understanding of the ecology of these sharks. Data were collected by accompanying landings and onboard in tuna fishing vessels in the western equatorial Atlantic Ocean off Brazil. A total of 138 bite wounds were found on the bigeye tuna (Thunnus obesus), common dolphinfish (Coryphaena hippurus), skipjack tuna (Katsuwonus pelamis), and yellowfin tuna (Thunnus albacares). The most bitten species were the bigeye and yellowfin tuna, together accounting for 85% of all bites. Our findings offer novel insights into ectoparasitic ecology between cookiecutter sharks and pelagic fishes, identifying three major patterns: (i) preference of the sharks for the ventral surface of pelagic fishes; (ii) plasticity in biting tactics, with both bottom-up and lateral attacks; and (iii) habitat-dependent bite incidence (larger sharks commonly bite the skipjack tuna in epipelagic zones, whereas smaller sharks predominantly bite the bigeye tuna in mesopelagic zones). These results contribute to narrowing the gaps in knowledge on the ecology of the elusive, dwarf cookiecutter sharks. Further studies are needed for a better understanding of how shark-pelagic fish interactions are affected by the fishing of aggregated schools.

Cookiecutter 鲨鱼是远洋外寄生虫，以大型海洋动物的肉块为食。关于这些鲨鱼的知识仍然很少，现有的少数作品成功地利用在猎物身上发现的叮咬来揭示生态模式。本研究旨在确定聚合鱼群中远洋鱼类的 cookiecutter 鲨鱼咬合模式，以了解这些鲨鱼的生态学。数据是通过在巴西近海的西赤道大西洋金枪鱼渔船上的登陆和船上收集的。大眼金枪鱼（ Thunnus obesus）、普通海豚（Coryphaena hippurus）、鲣鱼（Katsuwonus pelamis）和黄鳍金枪鱼（Thunnus albacares ）共发现138处咬伤。）。被咬伤最多的物种是大眼金枪鱼和黄鳍金枪鱼，占所有咬伤的 85%。我们的研究结果为 cookiecutter 鲨鱼和远洋鱼类之间的外寄生生态学提供了新的见解，确定了三种主要模式：（i）鲨鱼对远洋鱼类腹面的偏好；(ii) 咬人战术的可塑性，包括自下而上和横向攻击；(iii) 依赖栖息地的咬伤发生率（较大的鲨鱼通常在上层海域咬鲣鱼，而较小的鲨鱼主要在中层海域咬大眼金枪鱼）。这些结果有助于缩小对难以捉摸的侏儒鲨鱼生态学的知识差距。需要进一步研究以更好地了解鲨鱼与远洋鱼类的相互作用如何受到聚合鱼群捕捞的影响。