Estimation of annual bluefin tuna catch in weight by the troll fishery in Nagasaki prefecture [Japan], based on the Japanese official fisheries statistics
2007
Yamada, H.(National Research Inst. of Far Seas Fisheries, Shizuoka (Japan)) | Yamamoto, K. | Nitta, A.
Nagasaki Prefecture has the largest troll fishery for Pacific bluefin tuna Thunnus orientalis, which produces about a half of Japanese trolling catches of bluefin tuna every year. There is the Japanese official fisheries statistics compiled by the Ministry of Agriculture, Forestry and Fisheries of Japan, which produce the most reliable statistics in the long period. This statistics covers bluefin tuna catch by the troll fishery in Nagasaki Prefecture. However there are uncertainties in the bluefin tuna catch by trolling in Nagasaki Prefecture, since the statistics have problematic species category and changeable fishing gear category during a long series of compilation. In the statistics, the catch of small bluefin tuna is combined with longtail tuna (T. tonggol) etc. and categorized as the catch of small tunas. To segregate the bluefin tuna catch from the catch of small tunas, the ratio of bluefin tuna catch to the tunas was estimated based on the auction records from seven major landing ports in Nagasaki Prefecture for 1995-2002. We also found the missing tuna catches in the statistics in the 1960s, and tried to restore them. Finally, the annual catch in weight of bluefin tuna by the troll fishery in Nagasaki Prefecture was estimated during 1965-2002 in this study. The several years of the large catch were observed in the time series of the bluefin tuna catches, which was presumed caused by the strong recruitments migrating to the coastal area of Nagasaki Prefecture.
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