Diffusivity Summary of

Abundance indices for yellowfin tuna (Thunnus albacares) in the Gulf of Mexico for the period 1992-2002 were estimated using data obtained through pelagic longline observer programs conducted by Mexico and the United States. Individual longline set catch per unit effort data, collected by scientific observers, were analyzed to assess effects of environmental factors such as sea surface temperature and depth, time-area factors, and fishery factors such as bait and fleet. Standardized catch rates were estimated through generalized linear models by applying a Poisson error distribution assumption. A stepwise approach was used to quantify the relative importance of the main factors explaining the variance in catch rates. Sea surface temperature, year, area fished, time of set start, and quarter were the factors included in the final model. RÉSUMÉ Les indices d’abondance pour l’albacore (Thunnus albacares) en provenance du Golfe du Mexique pour la période 1992-2002 ont été estimés en utilisant des données obtenues au moyen des programmes d’observateurs de palangre pélagique menés par le Mexique et les Etats-Unis. Les données de capture par unité d’effort de chaque opération individuelle de palangre, recueillies par des observateurs scientifiques, ont été analysées pour évaluer les effets de facteur