Relações morfométricas de carcaças de tubarões-lixa (Ginglymostoma cirratum) e tubarões-tigre (Galeocerdo cuvier) do nordeste do Brasil

Abstract

Sharks and rays are essential to the oceans due to their ecological role. In general, these organisms have low fecundity and late sexual maturation. This makes them particularly susceptible to overfishing, which in turn makes it necessary to monitor the capture of these organisms. The landing of large sharks can be in the form of carcasses (without head, viscera, and fins). In this context, a length-weight relationship (LWR) can be useful for determining carcass weight when only length data are available. Relationships between lengths taken from shark carcass, including the interdorsal length (ID), can also be useful for monitoring and fisheries enforcement, as these relationships are length-length relationships (LLR). The goal of the present study was to determine the LWR of carcasses and LLRs for the sharks Ginglymostoma cirratum (sandbar shark) and Galeocerdo cuvier (tiger shark) captured off the coast of Northeastern Brazil. The captures were made by commercial fisheries using longlines on the continental shelf, from eastern Maranhão to northern Bahia, from November 2004 to February 2007. Carcasses of G. cirratum (n = 83) and G. cuvier (n = 26) specimens were analyzed after landing. For the LWR of carcasses, for nurse sharks, the equation obtained was: W = 5,461*10 -5 *CL 2,72 (R² = 0,947), representing an increase in growth with body elongation, a negative allometric growth; and for tiger sharks the equation was: W = 4.16*10 -5 *CL 2.78 (R² = 0,983), showing isometric growth, i.e., their body shape and condition do not change as they grow. To calculate the LLR, the equation for specimens of G. cirratum was generated: BP = -1.60 + 0.94*ID (N = 10) and AP = -1.89 + 1.02*ID (N = 11); and for individuals of G. cuvier: BP = -0.70 + 0.98*ID (N = 20) and AP = -0.82 + 1.02*ID (N = 21). The data analysis suggests that most of the sharks captured were juveniles or subadults, indicating that fishing pressure may be reducing the chances of reproduction for these species in the region. The nurse shark, classified as Vulnerable by the IUCN, has a low growth and reproduction rate, making it particularly sensitive to fishing. The tiger shark, despite its high fecundity, suffers significant impact due to excessive capture. The equations obtained in this study are potentially useful for estimating carcass weight, which is essential fishery data, as well as enabling the estimation of complementary morphometric measurements, contributing to the characterization of carcasses of these species landed. This could be useful for monitoring and fisheries regulation programs. This research addresses 'Sustainable Development Goal (SDG) 14,' one of the 17 SDGs established by the United Nations in 2015, which focuses on the conservation and sustainable use of oceans, seas, and marine resources for sustainable development.