Influence of oceanographic variability on recruitment of yellowfin tuna (Thunnus albacares) in the western and central Pacific Ocean

Recruitment estimates for yellowfin tuna (Thunnus albacares) in the western and central Pacific Ocean (WCPO), derived from a stock assessment model, are highly variable seasonally, interannually, and over decadal periods. A generalized linear model (GLM) was developed that predicts the variation in yellowfin tuna recruitment in response to a range of oceanographic variables. The GLM model accounted for 54% of the variation in quarterly recruitment for the pe- riod 1980-2003, with the inclusion of seven different oceanographic variables derived from a zone within the northwestern equatorial region of the WCPO. The robustness of the recruitment model was investigated by cross-validation. The GLM was complemented by a cluster analysis approach that identified five principal oceanographic states within the northwest- ern zone selected by the GLM. Incorporation of the recent GLM recruitment indices in the yellowfin tuna stock assessment model is likely to improve the precision of estimates of current and projected (next 1-2 years) biomass and exploitation rates. In a broader context, the recruitment model provides a tool to investigate how yellowfin tuna recruitment might vary in response to short- and long-term variation in the oceanographic conditions of the WCPO. Resume´ : Les estimations du recrutement de l'albacore anageoires jaunes (Thunnus albacares) dans l'ouest et le centre du Pacifique (WCPO), obtenues al'aide d'un modele d'evaluation des stocks, varient fortement en fonction de la saison et de l'annee et au cours des differentes decennies. Nous mettons au point un modele lineaire generalise ´ (GLM) qui predit la variation du recrutement de l'albacore a nageoires jaunes en reaction aune gamme de variables oceanographiques. Le modele GLM explique 54 % de la variation trimestrielle du recrutement pour la periode 1980-2003 avec l'inclusion de sept variables oceanographiques differentes mesurees dans une zone du nord-ouest de la region equatoriale de WCPO. Nous avons etudiela robustesse du modele de recrutement par validation croisee. Le GLM est completepar une methode d'analyse de groupement qui identifie cinq etats oceanographiques principaux dans la zone du nord-ouest retenue par le GLM. L'incorporation des indices recents de recrutement provenant du GLM dans le modele d'evaluation des stocks des albacores anageoires jaunes va vraisemblablement ameliorer la precision des estimations de la biomasse et des taux d'ex- ploitation courants et projetes (sur les prochaines 1-2 annees). Dans un contexte elargi, le modele fournit un outil pour de ´- terminer de quelle maniere le recrutement de l'albacore a nageoires jaunes peut changer en reaction aux variations acourt et a long termes des conditions oceanographiques de WCPO. (Traduit par la Redaction)

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