Caracterização das interações entre tubarão-charuto(Isistius spp.) e cetáceos ao longo de uma costa semiárida no Atlântico Equatorial Ocidental(1984 a 2024)

Abstract

The analysis of wounds and scars on in situ individuals or the investigation of stranded carcasses can serve as tools to study predator-prey relationships between sharks and cetaceans. Among the shark species that prey on cetaceans, the cookiecutter sharks Isistius brasiliensis and I. plutodus are found in epipelagic and bathypelagic waters and exhibit opportunistic feeding behavior. Despite their relatively small body length (up to 560 cm), these sharks are capable of attacking much larger marine animals, such as squids, large bony fishes, other elasmobranchs, pinnipeds, and cetaceans. Cookiecutter shark bite marks can be easily identified on prey due to the characteristic circular shape left by their distinctive dentition. However, due to their oceanic pelagic distribution, elusive behavior, and small size, cookiecutter sharks are relatively infrequently encountered by humans, resulting in knowledge gaps regarding their biology and feeding ecology. Therefore, this study aimed to characterize interactions between cookiecutter sharks and cetaceans along the equatorial semi-arid coast of Brazil. To this end, strandings recorded over a forty-year period (1984 to 2024) along the coast of Ceará were analyzed with regard to cetacean species, health condition of the individual, and body length, in addition to quantifying cookiecutter shark bites based on shape and healing stage. These data were obtained through monitoring conducted by the former Cetacean Study Group (GECC) and the subsequent NGO Aquatic Ecosystems Research and Preservation Association (Aquasis). Finally, the body length of I. brasiliensis individuals was estimated by measuring fresh circular bite wounds. Of the 1,070 stranded cetacean records analyzed, 4.86% (n = 52) presented marks caused by cookiecutter sharks. Among these, predation was predominantly observed in oceanic species that exhibit gregarious behavior and forage in demersal waters, such as Peponocephala electra, Stenella clymene, S. attenuata, and Globicephala macrorhynchus. The observation of fresh bites caused by cookiecutter sharks, coupled with the absence of a clear spatiotemporal pattern of strandings with such marks, may indicate the permanent presence of sharks of the genus Isistius spp. along the semi-arid equatorial Atlantic coast of Brazil. Moreover, through the estimated body length of I. brasiliensis, the data suggest a predominance of immature individuals in the region. In addition, the identification of specimens under 140 mm in length may indicate that the equatorial semi-arid Atlantic coast serves as a nursery area for cookiecutter sharks in Brazil.