Tendencias en la biomasa de sardina común (Strangomera bentincki) y anchoveta (Engraulis ringens) en la zona centro-sur de Chile, entre 1991 y 2005

common sardine (strangomera bentincki) and anchovy (engraulis ringens) constitute the main commercial small pelagic fishing activity in central-southern chile, with average annual catches between 1991 and 2005 of 342,000 tons (common sardine) and 405,000 tons (anchovy). abundance estimates for these species were obtained through statistical models of catch by age. these models incorporate information on annual catches, catch by unit of effort, biomass estimated by acoustic methods, size structure, and biological information (growth parameters, maturity, weight). parameter estimates were done using maximum verosimilitude methods. the analysis of the structure by age of sardine and anchovy catches shows a high presence of recruits and adult fraction that has decreased over time. the abundance levels were especially low for common sardine; the 2005 spawning biomass was 207,600 tons, as compared to the 485,000 tons estimated in 1991. common sardine recruitment (age group 0) was currently found to be 280,600 tons, lower than the 392,000 tons estimated at the beginning of the study period. for anchovy, the 2005 spawning biomass was 460,000 tons, as compared to the 415,000 tons of 1991, and 2005 recruitment was estimated at 275,000 tons, lower than the 291,000 tons of 1991