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III. B. Stock Assessment and Fishery Evaluation 



III.B.l. Trends in Catch-per-Unit-Effort 



81 ue marl in- -The catch-per-uni t-effort steadily declined 

 from 3.0 fish/1,000 hooks in 1952 to about 0.5 fish/1,000 hooks in 1975 

 (Figure 6 ). 



Striped marl in- -The catch rate for the entire Pacific 

 showed a slow, long-term decline from 1952 to 1975. The catch rate in the 

 North and South Pacific showed long-term declines since the 1950's (Fiqure 

 8 ) . 



Bl ack marl in- -The catch rate in the northwestern Pacific 

 (Area 1) reached a peak in 1954 and declined to its lowest in 1975 (Figure 

 10). In the southwest (Area 2), the catch rate reached a peak in 1955, 

 declined to less than 4 fish/10,000 hooks in 1'557, then fluctuated between 

 1 and 3 fish/10,000 from 1958 to 1975. The catch rate in the east (Area 3) 

 reached a peak in 1957 and declined thereafter. The western Pacific (Area 

 4) catch rate reflected the same trends as its constituent areas (Areas 1 

 and 2). 



III.B.2. Results of Production Model Analysis 



The following discussion of production model analyses on 

 the stocks of blue marlin, striped marlin, and black narlin is based on the 

 results of the Bill fish Stock Assessment Workshop held at the Honolulu 

 Laboratory from 5 to 14 December 1977 (Shomura 1980). 



Bl ue marl in- -Based on the assumption that the blue 

 marlin in the Pacific comprises a single oceanwide stock, production model 

 analysis gives a HSY estimate of 22,000 mt, which is associated with an 

 effective fishing effort equal to about 50% of the 1975 total effective 

 effort (Figure 11). This result, combined with the steadily decreasing 

 catch-per-unit-effort in spite of increased fishing effort, indicates the 

 stock is overfished (Shomura 1980). 



Striped marl in- -Assuming a single, oceanwide stock, the 

 MSY estimate is 24,000 mt at an optimum effective effort of 3.4 million 

 hooks/5° scuare (Figure 12). Considering the 1964-1975 catches of 14,500 

 to 27,100 mt at an average effective effort of 1.5 to 2.25 million hooks/5° 

 square, the MSY estimate infers a striped marlin population that is not 

 being overexploited. 



Assuming a two- stock population structure, a North 

 Pacific stock and a South Pacific stock, the results of the production 

 model analysis indicate a perplexing picture for the North Pacific stock 

 and a South Pacific stock that is being fished at about optimum level 

 (Figure 12). The catches in the South Pacific for 1973-75, however, were 



