Distribución, evaluación acustica y estructura poblacional de la anchoíta. Resultados de las campañas del año 1993

Two pelagic surveys to study were carried out during 1993. Those surveys covered the regions inhabited by either the bonaerensis stock in october (34-41°S)and the patagonian stock in November - December (41-45°30'S). Pre-stratified random sampling designs, including two random steps to allocate the transects, were adopted to perform the acoustic sampling by echo integration. A midwater trawl net (9-16 m vertical opening, 10 mm mesh-sized codend)was used to collect fish samples. The biomass of the northern stock was acoustically estimated to be about 1,45 million tons, whereas that of the southern stock was almost 740,000 t. Young anchovies, up to two-year old, allow for most of theose abundance values within each stock. The arrays of individuals at the sea both by size were calculated. There is some information supporting the picture of no increasing in anchovy total consumption by hake, as well as no main changes in natural mortality estimates. Most probably, the current biomass value has to be related to either a low reproductive success or recruitment as it is usual within Engraulids.