HANAN: BLUEFIN TUNA FISHERY 



18,000 



15,000 



BLUEFIN TUNA 



• • ANNUAL CATCH 



o o 10-YEAR RUNNING AVERAGE 



1925 



1945 1950 



YEAR 



1955 



1970 



FIGURE 1.— Annual catches of northern bluefin tuna in the eastern North Pacific Ocean for the years 1918-81. 



I8,000r 



1920 1930 1940 1950 1960 1970 1980 

 YEAR 



Figure 2.— Annual California landings (metric tons) of north- 

 ern bluefin tuna caught north and south of the United States- 

 Mexico international border, 1918-79. South is represented 

 by solid circles and lines, north by open circles and broken 

 lines. 



the 200-mi exclusive economic zone, much of the 

 data in this paper are separated into areas north 

 and south of lat. 32°N. A better division from a 

 biological standpoint would be north and south of 

 lat. 29°N (Fig. 4). 



The increase in California landings of bluefin 

 caught south of the border during the 1957-66 

 period can be attributed to increased fishing 

 effort, but the decline in catch north of the border 

 cannot be explained by declining effort, since ef- 

 fort remained comparatively level throughout 

 the period (Fig. 5). Because bluefin are valuable 

 ($l,180/short ton in 1981) and because fishing ef- 



fort north of the 32d parallel remained fairly con- 

 stant, the decline in northern catches is attrib- 

 uted to a decrease in abundance in that area. 

 During this period, increased catches south of 

 the border appear to have offset the decline in 

 catches to the north and to indicate the fish were 

 intercepted before migrating northward. If this 

 is true, the recent catch decline south of the bor- 

 der indicates declining bluefin abundance in the 

 eastern North Pacific. 



Catch and effort data summarized by latitude 

 show a bimodal distribution centering just north 

 of the 25th and 32d parallels (Table 3). The catch- 

 es are concentrated in the period June-Septem- 

 ber, with the largest catches shifting northward 

 during the fishing season (Fig. 4). Early in the 



15,000 

 12,500 - 



p 10,000h 



I 7,500 - 



o 



< 



<-> 5,000 



2,500 



\ ,\ / \ NORTH 



v v V __----" 



_L 



J_ 



1957 1960 1963 1966 1969 1972 1975 

 YEAR 



Figure 3.— Logged annual catches (metric tons) of bluefin 

 tuna north and south of lat. 32°N for 1957-69 and 1974. 



109 



