Spatial patterns of the yellowfin tuna (Thunnus albacares) in the Eastern Pacific Ocean: an exploration of concentration profiles

Abstract

The spatial distribution of the yellowfin tuna (Thunnus albacares) abundance in the Eastern Pacific Ocean was studied from commercial catches by the Mexican tuna-fishing fleet. Concentration profiles were carried out as indicators of a realtionship between catch-per-unit effort (CPUE) and fish abundance for the period from 1992 to 1996. Spatial and temporal resolution "units" were defined by means of a semi-variogram and serial correlation analyses, respectively. The unit resolutions obtained for catch data were 1 × 1 degree (spatial) and monthly (temporal). Catch values were standardized by means of robust regression. Fish resource spatial distribution patterns were identified and estimated catch-values were obtained with Generalized Additive Models. From these estimates, a CPUE time-space matrix CPUE was defined with 60 months and 1029 locations. Nine timespace patterns explained more than 80% of the variability. Individual spatial patterns were analyzed and spatial regions were defined with homogeneous CPUE values. Similarities between the CPUE and the concentration profiles (covered area) suggest that the CPUE-relative abundance relationship is not directly proportional which indicates hyperdepletion processes. Fishery management implications are also discussed in this study.