Age and growth of the Spanish chub mackerel Scomber colias off southern Spain: a comparison between samples from the NE Atlantic and the SW Mediterranean

This paper studies the age and growth patterns of the Spanish chub mackerel Scomber colias off southern Spain collected from two different areas, Atlantic coast and Western Mediterranean, from October 2003 to September 2004. The length-weight relationship was given by TW= 0.0015 TL 3.5289 (r² = 0.99, where TW= total weight in g, TL= total length in mm). Age was determined by interpreting and counting growth rings on the sagitta otoliths of 221 individuals caught by the commercial Andalusian fleet and during fisheries research surveys. Two rings, one opaque and one hyaline, were laid down each year on the otoliths. The opaque zone was formed during spring and summer and the hyaline one during autumn and winter. The otolith radius-length of the fish relationship was described by the equation: TL= 43.881 * OR1.245 (r²= 0.93, where OR= otolith radius). The parameters of the fitted von Bertalanffy growth curve were estimated for sex combined for the whole period (L_∞= 43 cm, K= 0.27 for the Gulf of Cadiz, and L_∞= 40 cm, K= 0.37 for the Alboran Sea, where L_∞ is defined as the asymptotic mean length and K is the rate at which the curve approaches the asymptote). There were no differences in growth rate between the sampling areas, suggesting that the Strait of Gibraltar is not a geographical break for the life history of this species; on the contrary, thanks to the similar environmental conditions of the Alboran Sea and the Gulf of Cadiz, the Strait of Gibraltar is a communication way that allows an Atlantic-Mediterranean larval flow.