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Fishery Bulletin 104(2) 



genetics is currently underway. Current information 

 from the western and central North Pacific implies that 

 salmon sharks constitute a single stock, but there is no 

 current information for the Japan Sea or the eastern 

 North Pacific (Sano, 1962; Tanaka, 1980; Blagoderov, 

 1994; Nagasawa, 1998). New technologies such as ar- 

 chival and pop-up satellite transmitters should provide 

 documentation of movements and migrations (Weng at 

 al., 2005) and key information as to whether regional 

 or international conservation and management plans 

 are needed. 



Stock structure may be an important factor in the dif- 

 ferential growth rates between ENP and WNP salmon 

 sharks. However, ecological differences between the ENP 

 and WNP could also be responsible for the observed 

 differences. Young salmon sharks appear to move from 

 temperate waters of the U.S. west coast into the Alaska 



Gyre and the Gulf of Alaska as they approach adult- 

 hood, which is when their growth rate begins to exceed 

 that of their WNP counterparts. These waters are ex- 

 tremely productive (Strub et al. 2001), and abundant 

 food resources may be the key factor in the differences 

 in growth rate, age-at-maturity, and weight-at-length 

 observed between ENP and WNP salmon sharks. 



A high degree of variability exists in the periodicity 

 of ring and growth band formation within and among 

 taxonomic groups of elasmobranchs, and much of the 

 variation observed in several lamniform sharks has not 

 yet been explained (Branstetter, 1990; Branstetter and 

 Musick. 1994; Wintner and Cliff, 1999). For example, 

 Cailliet et al. (1983) stated that shortfin mako sharks 

 (Isurus oxyrinchus) from the Pacific appear to form 

 growth rings annually, whereas Pratt and Casey (1983) 

 stated that Atlantic specimens appeared to produce two 



