Estimation of the relative annual abundance of yellowfin tuna, Thunnus albacares, in the Eastern Pacific Ocean during 1970-1985

ENGLISH: Estimates of relative annual abundance of yellowfin tuna in the eastern Pacific Ocean during 1970-1985 are made using catch rates, measured as tons caught by purse seiners per hour of searching. Catch rates are standardized a weighted generalized linear model. The important standardizing factors are vessel speed, season-area, and whether the yellowfin were caught in association with dolphins, skipjack tuna, or floating objects. Observations are weighted to give equal areas equal weight and to give each unit of fishing effort equal weight within an area. The results indicate that catch per days fishing underestimates abundance during the late 1970's when the fishery shifted some of its effort from dolphin sets to floating object sets, and overestimates abundance when the fishery shifted back to dolphin sets in 1984 and 1985. SPANISH: Se estima la abundancia anual relativa del atun aleta amarilla en el Oceano Pacifico oriental (OPO) durante 1970-1985 por medio de tasas de captura, calculadas como toneladas cortas capturadas por barcos cerqueros por hora de busqueda. Se usa un modelo lineal ponderado generalizado para estandardizar las tasas de captura. Los factores importantes de estandardizacion son la velocidad del barco, temporada-area, y si se capturaron los aletas amarillas en asociacion con delfines, barriletes, o objetos flotantes. Se ponderaron las observaciones para otorgar igual importancia a areas iguales y a cada unidad de esfuerzo pesquero dentro de un area. Los resultados senalan que la captura por dia de pesca estima por bajo la abundancia durante los ultimos anos de la decada de los 70, en cual epoca la pesqueria traslado parte de su esfuerzo de lances sobre delfines a lances sobre objetos flotantes, y la sobreestima al volver la pesqueria a lances sobre delfines en 1984 y 1985. (PDF contains 45 pages.)