Relationship between body size and geographic range size of elasmobranchs from the Tropical Eastern Pacific: An initial approximation for their conservation

Abstract

This study evaluated the relationship between body size and geographic range size, measured as extent and volume of occurrence of resident and endemic elasmobranchs of the Tropical Eastern Pacific. Data of body size, minimum and maximum depths, and latitudinal distribution of the species were obtained from the literature. Extent and volume of occurrence were measured from 3080.25-km² quadrants, considering the northern and southern boundaries, the maximum depth, and the depth interval of the 82 species included. The relationships between body size and depth, extent of occurrence, and volume of occurrence, and between body size and bathymetric zones were evaluated using linear regression and a nonparametric analysis of variance, respectively. The relationship between body size and extent of occurrence was positive for all groups and significant only for the batoids. They occupy smaller depth intervals than sharks and are almost exclusively restricted to the euphotic zone; the resident sharks occur in the three bathymetric zones, but not the endemic sharks. The interspecific relationship of body size and volume of occurrence revealed a triangle with defined boundaries, with 22 species under the constraint line (13 sharks and 9 batoids), Pristis sp. and Manta birostris being the most prone to extinction. Although there were no factors or characteristics common to all 22 species, variables such as habits and reproductive traits influence their vulnerability, in addition to the human pressures to which they are subjected. In elasmobranchs, the triangular relationship between body size and range size is a good predictor of species susceptible to extinction, which is useful for assessing the threat status and taking action for management and prioritization of species at regional level.