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III. STATUS OF STOCKS 



III. A. Stock Structure 



The stock structure of yellowfin tuna in the Pacific Ocean is not 

 perfectly clear but a hypothesis has been advanced that there are two 

 distinct stocks, one in the eastern Pacific and the other in the western 

 Pacific, separated by a less clearly defined stock in the central Pacific 

 (Suzuki et al . 1978). 



III.B. Stock Assessment and Fishery Evaluation 



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



In a study to examine the changes in catch-per-unit- 

 effort in the Japanese longline fishery, the Pacific Ocean was divided into 

 nine areas (Figure 4). After the first few years of fishing, the catch- 

 per-unit-effort fell sharply in most areas, then showed a relatively steady 

 and gradual decline as nominal effort increased (Figure 5). 



III.B. 2. Results of Production Model Analysis 



Although a production model analysis was not possible for 

 the combined surface and longline fishries for yell owf in tuna in the 

 western Pacific, an analysis (Honma and Suzuku^) was possible for the 

 entire Pacific longline fishery, which probably reflects the situation in 

 the western Pacific longline fishery (Figure 6). This analysis suggests 

 that the total effort is at or approaching the level producing MSY (maximum 

 sustainable yield), which is estimated at around 80,000 to 90,000 mt. 



III.B. 3. Results of Yield-per-Recruit Analysis 

 None available. 



III.B. 4. Results of Spawner/Recruitment Analysis 

 None available. 



^Honma, M., and Z. Suzuki. 1979. Stock assessment of Pacific yellowfin 

 tuna exploited by the tuna longline fihsery together with surface and 

 other fisheries in the western and central Pacific. Prepared for the 

 Workshop on the Assessment of Selected Tuna and Billfish Stocks in the 

 Indian and Pacific Oceans, Shimizu, Japan, 13-22 June 1979. 



