Spatial Patterns of the Yellowfin Tuna Thunnus albacares in the Eastern Pacific Ocean: An Exploration of Concentration Profiles

Yellowfin tuna abundance distributions in the eastern Pacific Ocean were studied using commercial tuna catch data from 1992-96. Spatial and temporal resolution units were defined and catch values were standardized using robust regression. Estimates of tuna distribution patterns were used to determine a catch-per-unit-effort (CPUE) time-space matrix. Nine time-space patterns explained more than 80% of the total variability. Analysis of spatial patterns and regions, and similarities between CPUE and concentration profiles indicate that a hyperdepletion process may be occurring. One explanation for the existence of such a process is that fish could be responding differentially to the extraction process, causing depletion of small but very vulnerable aggregations, leaving less vulnerable places nearby because of the heterogeneous distribution over the fishing zone.