Avaliação da estrutura populacional dos elasmobrânquios em um ecossistema insular no Oceano Atlântico Equatorial

Abstract

Observation per unit effort (OPUE) data were utilized to assess the population structure of elasmobranchs comprising the fauna of the São Pedro and São Paulo Archipelago (SPSPA) in the Equatorial Atlantic Ocean based on sightings during the period from 2008 to 2019. In this context, the overall objective of the study was to provide information about the population structure of elasmobranchs in the SPSPA fauna through sightings obtained during visual censuses in the region, aiming to contribute to the conservation of the island ecosystem and the species inhabiting the area. Throughout the study, 904 individuals were sighted during a sampling effort of 767 hours and 2 minutes of observation across 52 expeditions to the SPSPA. Rays represented 96.2% of the observations, with Mobula tarapacana being the most representative species (95.75%, n=833), followed by Mobula thurstoni (4.02%, n=35), and Mobula mobular (0.23%, n=2). Sharks accounted for 3.76% of the observations, exclusively belonging to the Carcharhinidae family, represented by the species Carcharhinus galapagensis (97.06%, n=33) and Carcharhinus falciformis (2.94%, n=1). Out of the total individuals sighted, the sex of 304 specimens was identified, with 188 being females, namely: 182 M. tarapacana, 1 M. thurstoni, and 5 C. galapagensis. For males, 116 individuals were identified, including 111 M. tarapacana, 4 M. thurstoni, and 1 C. galapagensis. Consistent variations in OPUE for the years and months of sampling indicate a trend in the occurrence of elasmobranch species in the SPSPA, with the highest annual values occurring in 2010 and 2015, and monthly values being prominent between February and August. According to IUCN criteria, only the Galapagos shark is not considered threatened with extinction in this study. Understanding the population structure of elasmobranchs is crucial for the management and conservation of species in the SPSPA, thereby contributing to the development of strategies to better understand the status of their populations and reduce their interaction with fishing activities.