Año 2002, Número 15: 85-94

Año 2002, Número 15: 85-94

Cordo, H.D. 2002. Efectos del filtrado de datos sobre la estimación de la tendencia de los índices de abundancia de polaca (Micromesistius australis).
Rev. Invest. Desarr. Pesq., 15: 85-94. Ver texto completo

Catch per unit of effort (CPUE) analysis of the argentine surimi fleet is a rutine work to estimate abundance indices of southern blue whiting (Micromesistius australis). Several analyses of this fishery suggest that, as of the years when intensive fishing by foreign and national fleets started, the resource has suffered a marked decline. When calculating the CPUE it is common practice to take into acount only trips and fishing operations with high catches of the target species; fishing operations directed to other species are not considered to avoid underestimations. Therefore, in order to include a percentage of catch of the analyzed species higher than a subjective value, available data are filtered. However, because only operations with high yield are considered, this kind of restriction can mask the true trend of the CPUE. In this paper the effects of data filtering on the estimation of abundance trends of southern blue whiting (SBW) in argentine waters for the period 1992-2000 are assessed. To analize the estimated mean values of abundance for the year a general linear model (GLM) was applied to data bases resulting from different levels of filtering. Results show that data filtering, in more or less degree, produce a false stability of the CPUE that leads to underestimation of the decline of SBW abundance. This fact became evident in 1997 when proportion of SBW in catches dropped significantly. Before 1997 the effects of data filtering were not evident because the fishery was practically monospecific with very high yields.