Inter-cohort growth variability and its implication for fishery management of the common sardine (Strangomera bentincki) stock off the coast of south-central Chile

Temporal and spatial variability in somatic growth of small pelagic fish populations has been recently acknowledged in a variety of stocks worldwide. We investigated the inter-cohort variability in length-at-age and somatic growth of the common sardine on the south-central coast of Chile. Using length frequency decomposition analysis of monthly samples from 1990 to 2006, we obtained the mean length-at-age and estimated 15 cohort specific asymptotic growth models (von Bertalanffy) with additional seasonal parameters. Results showed a conspicuous inter-cohort variability in the mean length and growth rate at different life stages throughout the first year of life. Striking anomalies (positive and negative) were observed during the 97/98 ENSO (El Niño South Oscillation), but the mechanisms behind these dynamics are unknown. Nevertheless, we investigated the impact of these variables on the optimal cohort yield. Simulations show that optimal age (month) to begin exploitation varies between cohorts, and a large portion of available cohort is lost by applying fishing mortality in a sub-optimal period. Therefore, monitoring size composition of each incoming cohort and use of an appropriate harvest strategy could help to better manage this resource and optimize fishery benefits.