Growth variability of mackerel (Scomber scombrus) off north and northwest Spain and a comparative review of the growth patterns in the northeast Atlantic.

Abstract

This paper studies the age, male and female growth patterns and the interannual growth variability during the 1990–2000 period of the northeast Atlantic mackerel (Scomber scombrus Linnaeus, 1758) off north and northwest Spain (ICES Divisions VIIIc and IXa north). Age was determined by interpreting and counting growth rings on the otoliths (sagitta) of 7732 individuals caught during the spawning seasons by the commercial fleet and during fisheries research surveys. The parameters of the von Bertalanffy growth curve were estimated for sex combined for the whole period studied (L∞=42.7 cm, k=0.268 per year, t0=−2.17 years) and for each year; for males (L∞=42.1 cm, k=0.276 per year, t0=−2.15 year) and females (L∞=43.0 cm, k=0.264 per year, t0=−2.21 year) for the whole period studied. The values of L∞ and k of the growth curves in males and females exhibited significant differences (likelihood ratio test, P<0.05) but not t0 (P=0.214). Length distributions by age group were compared by applying non-parametric tests (Kruskal–Wallis and Kolmogorov–Smirnov). Significant differences were found (P<0.05) between the years analysed, with high variability up to age 7. There were significant differences between sexes in some length distributions at age (Kolmogorov–Smirnov, P<0.05, ages 4–7, 9 and 11). The information obtained in this study was compared statistically with the available growth data for the mackerel in other geographic areas in the northeast Atlantic. The growth pattern showed variability along the geographical distribution range of the species. Spatio-temporal variability in the growth of mackerel would be taking into account in the stock assessment. The statistical differences between sexes found in growth pattern seem not implicate different behaviour, and a sex-specific assessment is not justified.