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III. STATUS OF THE STOCKS 

 III. A. Stock structure 



North Pacific bluefin spawn near the surface from April to July in 

 the Philippine Sea. Young fish remain near Japan and are fished by surface 

 gear until their first or second winter, when some migrate to the eastern 

 Pacific to enter the fishery during May to October. Data based on 11 

 transpacific tag returns show that the fish may remain in the eastern 

 Pacific 1 to 3 years before making the 2-year migration back to the 

 spawning grounds. Longliners probably exploit this returning migration. 

 Northern Pacific bluefin are also reported in the Australia-New Zealand 

 area, but the origin of these fish is unclear (Figure 3). 



III.B. Stock Assessment and Fishery Evaluation 



III.B.l. Trends in Catch- per-Un it-Effort 



This preliminary analysis is based on the summary data 

 for 1957 to 1966 from a recent California Department of Fish and 

 Game/National Marine Fisheries Service study, plus adjusted Inter-American 

 Tropical Tuna Commission (lATTC) figures for 1966 to 1979; both are 

 expanded to represent the eastern Pacific catch (Table 1). Over the 

 complete time series, the catch-per-unit-effort (CPUE) index declines 

 slightly (b = -0.123 per year), with a mean vaue of 2.45 mt per day (SD = 

 1.4). The mean CPUE for the most recent 12 years (x = 1.8, SD = 0.49) is 

 about half that of the previous 10 years (x = 3.28, SD = 1.72), while 

 nominal effort during this 22-year series has not significantly increased 

 (b = 0.07 per year) . 



III.B. 2. Results of Production Model Analysis 

 None available. 



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

 None available. 



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

 None available. 



