REVIEW AND ANALYSIS OF 



THE BLUEFIN TUNA, THUNNUS THYNNUS, FISHERY IN 



THE EASTERN NORTH PACIFIC OCEAN 



Doyle A. Hanan 1 



ABSTRACT 



Northern bluefin tuna migrate from waters near Japan to the eastern North Pacific where they are 

 fished primarily by purse seine. While annual catches fluctuate greatly, two major periods are 

 identified. The average annual catch in the second period ( 1950-present) is nearly double that for the 

 first period (1921-50) and is attributed to increased fishing effort by the "high-seas" tuna fleet oper- 

 ating off Baja California. The declining catch per unit effort in the second period and declining 

 catches after 1963 are assumed to indicate declining abundance of bluefin tuna in the eastern North 

 Pacific. 



Length-frequency analysis reveals 1) significantly smaller bluefin tuna in U.S. waters than in 

 waters off Baja California and 2) significant variation in mean lengths among years. 



Analysis of tag-recapture data confirms seasonal northward migration and vulnerability to the 

 fishery for as many as three fishing seasons. A catchability coefficient of 1.66 X l(T 4 /boat-day and 

 an annual instantaneous total mortality rate of 2.07, both estimated from the tag-recapture data, 

 are used with summaries of fishing effort to calculate an average annual exploitation rate of 30% 

 for bluefin tuna in the eastern North Pacific. 



Purse seining for northern bluefin tuna, Thun- 

 nus thynnus Linnaeus, in the eastern North Pa- 

 cific Ocean began about 1914, with the first large 

 commercial landings in 1918 (Whitehead 1931). 

 Prior to the development of this purse seine fish- 

 ery, a sport fishery existed off southern Califor- 

 nia at Santa Catalina Island; and since bluefin 

 tuna are difficult to catch by hook and line, elab- 

 orate fishing methods evolved such as using a 

 kite to make the bait (flying fish) skip across the 

 water (Clemens and Craig 1965). The Tuna Club 

 of Avalon at Santa Catalina Island even awarded 

 "blue buttons" to its members for catching the 

 large and wary prize. Because of this difficulty 

 in hooking bluefin, the commercial "high-seas" 

 fleet did not fish for bluefin until the late 1950's, 

 when most of the fleet had converted from pole- 

 and-line gear to purse seines (Bell 2 ). 



Currently the bluefin fishery consists of a "wet- 

 fish" fleet, principally out of San Pedro, Calif.; a 

 high-seas fleet mostly out of San Diego, Calif.; 

 and since 1975, an expanding Mexican fleet most- 

 ly out of Ensenada, Baja California. The bluefin 



'California Department of Fish and Game, c/o Southwest 

 Fisheries Center, National Marine Fisheries Service, NOAA, 

 P.O. Box 271, La Jolla, CA 92038. 



2 Bell, Robert R. 1970. Bluefin tuna Thunnus thynnus ori- 

 entalis in the northeastern Pacific Ocean. Unpubl. manuscr. 

 Calif. Dep. Fish Game, 350 Golden Shore, Long Beach, CA 

 90802. 



Manuscript accepted Julv 1982. 



FISHERY BULLETIN: VOL. 81, NO. 1. 1983. 



fishery extends along the coast of North America 

 from Cabo San Lucas, Baja California, to Point 

 Conception, Calif., and occasionally farther north 

 (Table 1). The bluefin catch is composed mainly 

 of 1-, 2-, and 3-yr-old fish, which appear to mi- 

 grate to the eastern North Pacific from the west- 

 ern Pacific near Japan (Schultze and Collins 

 1977); however, older and much larger bluefin 

 are reported and occasionally caught in the east- 

 ern North Pacific. 



This paper reviews and analyzes the bluefin 

 tuna fishery in the eastern North Pacific, using 

 data collected by the California Department of 

 Fish and Game (CFG) in cooperation with the 

 Inter-American Tropical Tuna Commission 

 (IATTC), and the National Marine Fisheries 

 Service (NMFS) of the U.S. Department of Com- 

 merce. 



CATCH AND EFFORT ANALYSIS 



Although annual bluefin catches have fluctu- 

 ated considerably in the eastern North Pacific 

 (Table 2), two major periods are identified in the 

 catch by a plot of a 10-yr running average (Fig. 

 1). During the first period, about 1921-50, total 

 landings averaged 5,066 t (metric tons)/yr and 

 were declining toward the end of the period. 

 During this time, bluefin were landed almost ex- 



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