The determination of maturity stages in male elasmobranchs (Chondrichthyes) using a segmented regression of clasper length on total length

Abstract

A novel statistical method for estimating the stages of maturity in male sharks and skates based on a segmented regression (SRM) is proposed. We hypothesize that this method is able to find the transition points in the three-phase relationship between total length (TL) and clasper length (CL). We applied an SRM to TL–CL data of nine species, from large pelagic sharks (e.g., Carcharhinus falciformis) to small coastal skates (e.g., Rioraja agassizi), captured in the southwestern Atlantic and northeastern Pacific. As expected, SRM detected two breakpoints, defining three maturity stages (immature, maturing, and mature), in six out of nine species. For three species, it was not possible to find two breakpoints because of incomplete sampling of TL. This novel method is noninvasive, it is applicable to previously collected data, is easy to use, and provides a reliable tool for increasing our understanding of elasmobranch reproductive strategies.