Changes in growth and maturation parameters of Pacific sardine Sardinops sagax collected off California during a period of stock recovery from 1994 to 2010

Whether fluctuation in density influenced the growth and maturation variables of three aggregated cohorts (fish born during the 1986-1993, 1996-2003 and 2004-2008 periods) of Pacific sardine Sardinops sagax caeruleus collected off the Californian coast from 2004 to 2010 was investigated. Using a von Bertalanffy mixed-effects model with aggregated cohorts as covariates, estimated growth rate significantly covaried with aggregated cohorts. Growth rate (K) was modelled as a fixed effect and estimated to be 0264 +/- 0015 (+/- s.e). Statistical contrasts among aggregated cohorts showed that the 1996-2003 cohorts had a significantly lower growth rate than the other two aggregated cohorts. The theoretical age at length zero (t(0)) and the standard length at infinity (L-S) were modelled as random effects, and were estimated to be -2885 +/- 0259 (+/- s.e) and 27313 +/- 6533mm (+/- s.e). The relation of ovary-free mass at length was significantly different among the three aggregated cohorts, with the allometric coefficient estimated to be 2850 +/- 0013 (+/- s.e) for the S. sagax population. The age-at-length trajectory of S. sagax born between 1986 and 2008 showed strong density dependence effects on somatic growth rates. In contrast to the density-dependent nature of growth, the probability to be mature at-size or at-age was not significantly affected by aggregated cohort density. The size and the age-at-50% maturity were estimated to be 15092mm and 056years, respectively. Stock migration, natural fluctuations in biomass and removal of older and larger S. sagax by fishing might have been interplaying factors controlling growth parameters during 1986-2010.