Estimates of exploitation rates for north Pacific albacore, Thunnus alalunga, from tagging data

North Pacific albacore tagging data from a tag-release program conducted fr om 1971 to 1989 were analyzed to obtain estimates of exploitation rates and related parameters. The major albacore fishing fleets in the North Pacific , the U.S. baitboat, Japan baitboat, troll and longline fleets were used in the analysis. Another category of fleet ("other") that combined remaining miscellaneous recapture sources was also used. Tag-attrition models incorpo rating variable availability of tagged albacore to the various fleets, seas onal catchability, and multiyear effects on catchability were developed and applied. The incorporation of all three effects was found to improve model fit significantly. If exploitation of the tagged population is representat ive of the North Pacific albacore population as a whole and if tag reportin g rates were high, the results would suggest that the exploitation rate has been less than 10% per year since the early 1970s. However, a deficit of r eturns from the troll fleet in comparison with its catch suggested that the pattern of exploitation of the tagged population, by this fleet at least, was different from that for the untagged albacore population. After compens ating for assumed depressed availability of tagged albacore to the troll fl eet, annual exploitation rates were estimated to have declined from a high of 40% in the mid-1970s to <10% since the early 1980s.