DAYS AT LIBERTY 



,400 



Figure 16. --Di stance from site of tagging as a function of time at liberty. 



Note that the shorter term recoveries are plotted on an expanded scale. 



Data are from Otsu and Uchida (I963). (15 miles = 27.8 km., 10 miles = 18.5 



km. , 5 mi les = 9. 3 km. ) 



if it were not capable of soaring, and the fact 

 that tagged tunas have been known to be cap- 

 tured at essentially the same location as that 

 in which they were tagged after several weeks 

 at liberty. Since our considerations are re- 

 stricted mostly to ''apparent" movement, our 

 conclusions relative to the actual movements of 

 the albacore are of course, to a large extent, 

 speculative. 



MIGR.\TORY ROUTE 



An understanding of yield-per-recruit and 

 other dynamical problems relevant to the alba- 

 core on the North Pacific longline grounds de- 

 pends, to a large extent, on an understanding of 

 the nature of albacore immigrations and emi- 

 grations from the various fisheries in the North 

 Pacific Ocean. Models describing these immi- 

 grations and emigrations have been forwarded 

 in the literature. In this section we review 

 these models in relation to our study of the 

 spatial statistics. 



Our present understanding of the migration 

 of albacore over the entire North Pacific Ocean 

 is essentially based on the work of Clemens 

 (1961, 1963) and Otsu and Uchida (1963). The 

 model formulated by Clemens established the 

 relationship between those albacore taken in 

 the coastal waters of North America and those 

 taken by the Japanese fisheries of the North 



Pacific. According to Clemens the albacore 

 are first recruited to the North American fish- 

 ery off the coast of California, move north 

 along the coast and then west, continuing along 

 the subtropical convergence until they encounter 

 the Japanese fisheries. The model proposed by 

 Otsu and Uchida (subsumed in figure 9 of their 

 paper and reproduced here as fig. 17) is in 

 many respects similar to that of Clemens, but 

 is more explicit in describing the clockwise as 

 well as the more typical counterclockwise 

 movements and postulating a definite pattern of 

 the mode of entrance of the North American 

 escapement into the Japanese fisheries: viz, 

 from North American, to longline, to pole and 

 line. 



The evidence presented by Otsu and Uchida 

 and by Clemens clearly confirms that at least 

 the majority of albacore taken in the Japanese 

 fishery are emigrants from the North Ameri- 

 can fishery. It is not clear, however, that the 

 albacore move directly from the North Ameri- 

 can to the longline and then to the pole-and-line 

 fishery. We believe, rather, that a large pro- 

 portion of the albacore that emigrate from the 

 North American fishery first enter the pole- 

 and-line fishery (we emphasize that our infer- 

 ences with respect to movement are fishery- 

 specific and therefore our statement that the 

 albacore "first enter the pole-and-line fish- 

 ery" does not preclude the possibility that 



23 



