UPDATE OF STANDARDIZED CATCH RATES OF LARGE BLUEFIN TUNA (THUNNUS THYNNUS) FROM THE U.S. PELAGIC LONGLINE FISHERY IN THE GULF OF MEXICO 1987-2013 WITH CORRECTION FOR WEAK HOOK EFFECTS

SUMMARY An updated index of abundance of bluefin tuna was constructed from logbook reports from the U.S. pelagic longline fishery in the U.S. Gulf of Mexico for the period 1987-2013. The index is an update of the index presented for the 2012 assessment and subsequently updated at the 2013 Species Group meeting.The index was constructed using vessel as a repeated measure to account for the variance in catch rates within vessels, and was standardized using two stage Generalized Linear Mixed Models with separate binomial and a lognormal models. In 2011 vessels were required to use a weak hook that would bend due to pressure from a large fish as a means of reducing bycatch of bluefin tuna. Extensive experiments have determined that these hooks result in a 46% (23-62%CI) reduction in the catch rates of bluefin tuna. Indices for2011, 2012 and 2013 were adjusted upwards by a factor of 1.108,1.85 and 1.85, respectively to account for this expected reduction in CPUE. Adjusted index values for 2012 were among the highest three in the time series and appear to indicate an increasing CPUE trend in recent years, which would not have been estimated to have been as high in the unadjusted index. However, the index has appeared to decline in the 2013. Due to management actions that appear to be impossible to model, we recommend splitting the index between 1991 and 1992. RESUME