366 



Fishery Bulletin 101(2) 



California and Mexico, all from outside tag release areas. 

 These rather remarkable recaptures do provide evidence 

 for the trans-Pacific connection of spiny dogfish stocks but 

 pose the question of the significance of such east to west 

 exchanges. One possible significance would be the transfer 

 of genetic material. The fact that these recaptures occurred 

 regularly from 1982 to 2001 suggests ongoing migration be- 

 tween areas. Two recent recoveries off Japan support this 

 hypothesis. One fish, a 69-cm female was released off the 

 west coast of Vancouver Island in 1984, and the other, also 

 a female (72-cm) was released in the Strait of Georgia in 

 1988. Both fish were recovered in May 2001 off Hokkaido. 

 Although the evidence is limited, and the magnitude of 

 the exchange between eastern and western Pacific stock, 

 and indeed northern Canadian fish and those off southern 

 California and Mexico, is small, it is clear that the inter- 

 relationships between these areas needs to be examined if 

 ecosystem management incorporating these apex preda- 

 tors is to be developed. 



In the eastern North Pacific, the management of spiny 

 dogfish was recently identified as a priority by the Ameri- 

 can Fisheries Society (Musick et al., 2000). In addition, the 

 global decline in many shark populations, and in particular 

 spiny dogfish in the Atlantic ocean (Stevens et al., 2000), 

 raises the question: What are the effects of the removal of 

 large numbers of sharks (spiny dogfish) on marine ecosys- 

 tems? A recent attempt (Stevens et al., 2000) to examine 

 this question (albeit a somewhat simplistic one) identified 

 a number of significant ecological and economic impacts. 

 The study illustrated that under differing conditions, the 

 consequences of depleting sharks in certain ecosystems are 

 complex and could lead to unforeseen consequences that 

 extend beyond the fished ecosystem. The highly migratory 

 nature of many shark species complicates management 

 efforts (Musick et al., 2000), and adding to the complexity 

 are relationships between distribution, migration, and en- 

 vironmental conditions, such as those documented for blue, 

 salmon, and thresher sharks in the northern Pacific (Holts, 

 1988; McKinnell and Seki, 1998; Bigelow et al., 1999). The 

 development of effective ecosystem-based management 

 hinges on understanding the implications of indirect 

 and direct impacts on ecosystem structure and function 

 (Fogarty and Murawski, 1998) and will require improved 

 understanding of 1) species interactions, i.e. what, when, 

 and where dogfish eat, and what eats dogfish, 2) migration 

 patterns (both seasonal and long term) from and between 

 all ecosystems within the range for dogfish (identified in 

 this report), and 3) changes in migration and distribution 

 in relation to changing climate and ocean conditions. To 

 date, the effects of the removal of large numbers of spiny 

 dogfish remain essentially unexamined, in part because of 

 the limited information in each of these three areas. 



Acknowledgments 



Wo thank Bill Andrews, Brad Beailli, Mark Saunders, 

 Mike Smith, and Maria Surry for conducting field work, 

 maintaining databases, and preliminary production of 

 tables and figures. 



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