Age and growth of the blackchin guitarfish Glaucostegus cemiculus (Geoffroy Saint-Hilaire, 1817) from Iskenderun Bay (Northeastern Mediterranean)

Abstract

Between September 2010 and June 2012, a total 291 (166 females and 125 males) blackchin guitarfish Glaucostegus cemiculus were captured by a commercial bottom trawler (F/V Coskun Reis) in Iskenderun Bay, Turkey (northeastern Mediterranean Sea). The total length (L) and total weight (W) of the female and male guitarfish ranged between 32.0-165.0 cm and 88 g-16.68 kg, and 34.3-128.3 cm and 112 g-6.00 kg, respectively. Vertebral age estimates ranged from 0 to 8 years for females and 0 to 5 years for males. The growth models of von Bertanlanffy and Gompertz were fitted to the length at age data using the nonlinear regression method. Model selection was based on the values of the residual standard error and the Akaike's information criterion corrected for small sample size (AIC(C)) associated with each fit. The von Bertalanffy growth model provided the best fitting growth curves for each sex with parameters reaching L-infinity = 187.17 cm, K = 0.195 year(-1), t(0) = -1.38 year for females, and L-infinity = 144.85 cm, K = 0.321 year(-1), t(0) = -1.13 year(-1) for males. The W-L relationship parameters did not differ significantly between sexes, the estimated values of a and b were 0.0018 and 3.11, respectively. By using these values of a and b, and also respective estimates of L-infinity, the values of W-infinity were obtained as 20.53 kg for females and 9.25 kg for males. The overall percentage ratios of females and males in the samples were 57% and 43% respectively.