YELLOWFIN TUNA, THUNNUS ALBACARES, CATCH RATES IN 



THE WESTERN PACIFIC 



Tom Polacheck' 



ABSTRACT 



The surface fishery for yellowfin tuna, Thunnus albacares. in the western Pacific has increased drama- 

 tically since 1978. Catch and effort statistics from the Japanese purse seine and longline fisheries are 

 examined in terms of changes in catch rates and the interaction between these two fisheries. In spite 

 of a 10-fold increase in surface catches to around 100,000 metric tons per year, purse seine catch rates 

 have remained relatively constant. Longline catch rates since 1980 have been declining, with the excep- 

 tion of high rates in 1983. Comparison of purse seine and longline catch rates within the same area and 

 time period indicated no relation between them and suggests that the yellowfin tuna stocks are not 

 homogeneous with respect to the two gears. In addition, observed changes in longline catch rates within 

 areas of the western Pacific appear not to be related to the magnitude of the purse seine catches within 

 these areas. The results provide no direct evidence for any interactions between the two gears, but whether 

 purse seine catches are contributing to the possible, overall decline in longline catch rates remains an 

 open question. 



Purse seine catches of yellowfin tuna, TMmnus alba- 

 cares, in the western Pacific have increased from 

 8,000 to 10,000 1 (metric tons) in 1978 (Habib 1984^) 

 to estimates of around 100,000 t in 1984. Prior to 

 the advent of purse seining, the main vessels har- 

 vesting yellowfin tuna in this region were the Japa- 

 nese, Korean, and Taiwanese longliners. Longliners 

 still continue to harvest significant amounts of 

 yellowfin tuna (an estimated 60,000 t in 1984). The 

 effect of this 10-fold increase in purse seine catches 

 since 1978, both on the overall stocks of yellowfin 

 tuna in the western Pacific and the effect of the 

 purse seine catches on the longline fisheries, is un- 

 known, but the status of yellowfin tuna stocks is a 

 critical question for a number of reasons. Yellowfin 

 tuna represent the second largest fishery resoiu-ce 

 for the tropical western Pacific area. Yet, there is 

 no adequate assessment of the magnitude of the 

 harvestable catch for the region, while yellowfin 

 tuna stocks in other regions appear vulnerable to 

 overexploitation by purse seiners (lATTC 1979, 

 1980, 1981, 1982; Fonteneau and Diouf 1983; Au 

 1983). In addition, about two-thirds of the yellowfin 

 tuna longline catch is targeted for the Japanese 

 Sashimi market and, as such, has an economic value 



'Tuna and Billfish Assessment Programme, South Pacific Com- 

 mission, B.P. D5, Noumea Cedex, New Caledonia; present address: 

 Northeast Fisheries Center Woods Hole Laboratory, National 

 Marine Fisheries Service, NOAA, Woods Hole, MA 02543. 



^Habib, G. 1984. An overview of tlie purpose seine tuna fish- 

 ery in the central/western Pacific and development opportunities 

 for island states. Workshop on National Fishing Operations, 

 Tarawa, Kiribati, 28 May-4 June 1984. 



Manuscript accepted August 1988. 

 Fishery Bulletin, U.S. 87:123-144. 



exceeding that of the purse seine-caught fish. Long- 

 liners harvest older and larger fish than purse 

 seiners (Cole 1980). In the present paper, the most 

 recent data available on the catch and effort for 

 yellowfin tuna are examined for information on the 

 current yellowfin tuna stocks and on the interaction 

 between longline and purse seine fisheries. 



METHODS 



Data 



The data available for examining catch rates come 

 from records of daily catch and effort supplied by 

 vessels to individual island states in the western 

 Pacific as part of access arrangements which allow 

 vessels to fish within the 200-mile EEZ's (Exclusive 

 Economic Zone) of these states. These catch records 

 have been subsequently transmitted to the Tuna and 

 BOlfish Assessment Programme of the South Pacific 

 Commission (SPC), and have formed the core of the 

 regional statistical data base. Data are only supplied 

 as a requirement of access for fishing within EEZ's. 

 While some vessels include activity in international 

 waters in their reports, the available data are rela- 

 tively incomplete for these waters. Also, for some 

 states in past years, adequate data reporting was 

 not included in the access ag'-eements. In addition, 

 prior to 1984 almost no data are available from 

 United States and some other eastern Pacific purse 

 seiners. 



Because of incompleteness and limitations in the 



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