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

Pan-Atlantic distribution patterns and reproductive biology of the bigeye thresher, Alopias superciliosus

“…In addition, a segmented regression model (SRM) was used to estimate the transition points and slopes in the regression between fork length and clasper length. These breakpoints have been defined to identify the three FL intervals with different slopes that represent the three maturity stages of male elasmobranchs: ''immature'', ''maturing'' and ''mature'' (Segura et al 2013). Thus, the breakpoints are defined as the values of the explanatory variable (FL) at which the changes in slope occur (Muggeo 2003).…”

“…The fact that the median size at maturity estimated through the maturity ogive (L 50 = 159.2 cm FL) is included between the two breakpoints of the regression, seems to support the effectiveness of this method. Furthermore, other authors have used this approach as it provides an objective and direct estimate of the maturity stages of male elasmobranchs (using only clasper measurements) instead of relying on a subjective classification which depends on the observer's ability and may vary between different observers (Segura et al 2013). In addition, it is a non-invasive method and can be applied to existent common fisheries data (Segura et al 2013).…”

Metabolic dependence of phytoplankton species richness

“…For a detailed description of the piecewise regression fitting method we refer to Muggeo () and for examples of biological applications to Segura et al . () or Toms & Lesperance ().…”

Sexual development and maturity scale for the angel shark Squatina squatina (Elasmobranchii: Squatinidae), with comments on the adequacy of general maturity scales

“…Additionally, Capapé et al (1990Capapé et al ( , 2002 used clasper length to separate juvenile, subadult and mature phases. Segura et al (2013) validated that the estimation of the breakpoints and slopes in the total length to clasper length relationship based on a segmented regression model (Muggeo 2003) can discriminate among these phases for S. guggenheim, among others, regardless of the life history strategy or the habitat of the species.…”

“…Walker 2005, Segura et al 2013; therefore, only 'fully calcified', 'functional' and 'not calcified' were described. In cases where more details of clasper development are required, length is a more accurate parameter because it can be clearly defined and measured (Segura et al 2013). Additionally, Capapé et al (1990Capapé et al ( , 2002 used clasper length to separate juvenile, subadult and mature phases.…”