Inter-cohort growth rate changes of common sardine (Strangomera bentincki) and their relationship with environmental conditions off central southern Chile

The inter-cohort variability in the von Bertalanffy (VB) growth parameters of common sardine (Strangomera bentincki) was analyzed for the period between 1990 and 2007. Time series of monthly length–frequency data were used to study the growth of the species. The MIX software was used to separate normal components and modal progression analysis was used to identify cohorts that have recruited each year. The VB growth parameters were estimated using nonlinear mixed-effects model (NLME) by considering that the population growth parameters have a common distribution, and that cohort-specific parameters can be treated as random effects. A model that considered L∞ (asymptotic length) and K (growth coefficient) as random effects was the best in explaining inter-cohort changes in body growth. The growth rate during the first fast-growing period of sardine cohorts exhibited a significant change after 1998. Cohorts recruited between 1990 and 1997 showed higher growth rates than cohorts recruited from 1999 to 2006. This significant change is coincident with a colder period established in the area after 1998, and with a significant increment in the Ekman transport. Sea surface temperature anomalies explained 46.2% of the variability observed in the early growth rate of the cohorts. It is concluded that environmental conditions encountered by the cohorts during the spawning period could modulate the growth rate of common sardine year to year, but the possibility of further intrinsic factors affecting the growth dynamics of common sardine could be also important and deserve to be considered in future studies.