NOTE Stanley et al.: Movements of tagged Sebastes flavidus 



661 



Washington were recovered in Queen Charlotte 

 Sound. However, landings of yellowtail rockfish in 

 Queen Charlotte Sound were also low in the years 

 during, and the first three years following, tagging 

 (Table 4). 



The yellowtail rockfish tagged in the Alaskan study 

 were caught in waters shallower than 30 m and were 

 predominantly immature. A southward, ontogenetic 

 migration to the broader continental shelf off cen- 

 tral B.C. is possible. This would parallel the move- 

 ment of immature yellowtail rockfish from Puget 

 Sound to the outer Washington coast (Mathews and 



Barker, 1983 ). However, many of these fish may sim- 

 ply move west towards the deeper water on the outer 

 shelf but remain within southeastern Alaska. The 

 limited commercial fishery in these outside waters 

 prevents resolution of these alternatives, although 

 they are not mutually exclusive. 



We suggest that the low recovery rate for the Ca- 

 nadian study was caused by short-term post-tagging 

 mortality arising from a combination of the greater 

 depth of capture, the greater stress from trawl cap- 

 ture compared with hook-and-line, and the added 

 handling during anaesthetization, decompression, 

 and OTC injection. The dosage level of OTC may have 

 also contributed to mortality, as studies on other spe- 

 cies have shown increasing mortality with dosages 

 greater than 25 mg/kg body weight (McFarlane and 

 Beamish, 1987). 



An alternative explanation for low recovery rates 

 in the Canadian study is that the tagged fish were 

 released into very large populations, well in excess 

 of current estimates (Table 4). Thus, landings of 400- 

 900 t in the early 1980s provided little chance for 

 recovery. However, this same logic should then ap- 

 ply to the likelihood of recapturing Alaskan tags in 

 the B.C. fishery at the same time. Since this recov- 

 ery ratio was much higher, the Alaskan results sup- 

 port the contention of high initial mortality in the 

 Canadian study. 



The rate of recovery for Canadian tags was low at 

 the outset and gradually declined over the ten years 

 after release. The 95% confidence limits of the point 

 estimate for the instantaneous rate of decline over 

 the ten years (0.099-0.307) is consistent with the 

 range of extinction rates (0.28- 

 0.54) predicted by combining pub- 

 lished estimates of instantaneous 

 rates for natural mortality, 0.06- 

 0.12 (Archibald et al., 1981; 

 Tagart, 1991), tag loss for black 

 rockfish, 0.13 (Lai and Culver, 

 1991), and fishing mortality for 

 yellowtail rockfish off northern 

 Washington, 0.09-0.29 (Tagart, 

 1991). 



Despite the commercial impor- 

 tance of this species, the stock 

 boundaries are poorly understood. 

 Assessment biologists have re- 

 sorted to selecting boundaries 

 based on a combination of official 

 statistical areas and on the distri- 

 bution of major fishing grounds. 

 The most recent assessments have 

 assumed four stocks from group- 

 ings of International North Pacific 



