Interannual changes in size-at-maturity of common sardine, Strangomera bentincki, in the central-southern zone of Chile (2007-2012)

Interannual changes in size-at-maturity (Lm ) of common sardine, Strangomera bentincki, were evaluated for the period 2007-2012 in the south-central area of Chile. Data consisted of microscopic maturity stages of female ovaries, which were collected during the reproductive peak each year. Immature females were identified from mature females and a logistic model was fitted to data through generalized linear model (GLM) and generalized linear mixed model (GLMM). The best model was characterized by having both variable slope and intercept, revealing significant interannual variations in size-at-maturity. Although the average length of the immature fraction showed a tendency to decline over time, interannual changes in size-at-maturity varied at random between 8.4 and 12.7 cm, and around Lm = 10.7 cm total length. It is concluded that GLMM technique was suited to representing interannual random changes in size-at-maturity of common sardine. There was no trend to diminish according to the hypothesis of truncation of size/age due to fishing intensity. Rather, the random expression in size-at-maturity could be a consequence of factors associated with sampling, growth or delayed response in maturity due to spatio-temporal asynchrony in the reproductive process.