Estimating some population parameters and stock assesment of spiny butterfly ray, Gymnura altavela (Linnaeus, 1758) the Levant Basin coast (Northeastern Mediterranean)

Abstract

The purpose of this study was to investigate the morphometric characteristics, growth, mortality and exploitation rate of the spiny butterfly ray (Gymnura altavela Linnaeus, 1758). The study was conducted using 284 specimens from the coastal waters of the Levant Basin (the northeastern Mediterranean). Samples were collected monthly between July 2014 and June 2015 using a bottom trawl from the following depth strata: 0-10m, 10-20m, and 20-50m. The following measurements were taken total length (TL), disc length (DL), disc width (DW) distance from nose tip to eye (NE), nose tip to mouth (NM, cm), width of mouth (MW, cm) where Y is the various dimensions (TL; W; DL; DW; NE; NM; MW, respectively) and X is the total length estimated by linear regression analysis. Length-weight and disc width-weight relationships were W = 0.097 * TL3.2070 and W = 0.084 * DW3.169 for total individuals. The von Bertalanffy growth function contained in DW was DW¥ = 136.50cm K = 0.230 year-1 t0= -0.492year-1 for total individuals. The total mortality (Z) was 0.91year-1, the natural mortality (M) was 0.41year-1, and the fishing mortality (F) was estimated to be 0.51year-1. The exploitation rate (E) was calculated as 0.55 year-1 for all obtained individuals.