Stanley and Kronlund: Life history characteristics for Sebostes brevispims 



677 



data. The first is that while the overall 

 number of samples and specimens is large, 

 they are not equally distributed over time 

 and space. Thus, for example, we cannot 

 examine whether larger or older males 

 complete the mating earlier in the season 

 because of the lack of winter samples. The 

 second implication is that the results are 

 influenced by the fishing practices. This 

 is particularly the case for inferring depth 

 distribution from trawl catches. 



Habitat 



Silvergray rockfish appeared to be concen- 

 trated in the 100-300 m depth interval. 

 Their distribution tended to overlap the 

 distribution of "slope" and "shelf" assem- 

 blages of Weinberg (1994) that were based 

 on survey results from northern California 

 to southern British Columbia. The dis- 

 tribution also agrees with observations 

 from research surveys in B.C. waters (Nag- 

 tegaal, 1983). Peak catch rate at depth 

 indicates an annual depth migration, noted 

 by fishermen, of about 80 m. The timing 

 and range of this movement is considered 

 by fishermen to be typical for rockfish 

 (Dickens 7 ). 



The movement appears correlated with 

 temperature. Bottom temperature increases 

 in winter owing to downwelling (Fig. 2) 

 (Thomson 6 ). Thus, the shift to shallower 

 water in the summer means that peak 

 catch rates throughout the year are found 

 in waters centered at just over 7°C. The 

 apparent seasonal movement has obvious 

 implications for stock assessments. Sur- 

 veys designed to track abundance among 

 years need to be consistent with respect to 

 their timing and depth. More importantly, 

 those who attempt to use CPUE to moni- 

 tor abundance must consider changes in 

 the distribution of fishing effort by season 

 among years. 



There has been no research on the larg- 

 er scale movements of silvergray rockfish. 

 Barotrauma induced during traditional 

 trawl or hook-and line-fishing precludes 

 tag-recapture studies, although recent work 

 on other rockfish indicates there is poten- 

 tial for tagging in situ (Schrope, 2000; 

 Starr et al., 2001). Nor do we know of any 

 genetic studies on silvergray rockfish to 

 determine stock structure, although the 



10 



12 



0,0 



0.7 O 



0.5 O 



0.3 O 



0.1 ° 



10 12 



Month 



Figure 4 



The proportion of each maturity stage within each month for (Al female 

 and (B) male silvergray rockfish (Sebastes brevispinis) (see Table 1 for 

 definition of stages represented by the numbers on the y axis). 



Dickens, B. 2000. Personal commun. 1678 

 Admiral Tryon Boulevard. Qualicum Beach, 

 British Columbia VOR 2T0, Canada. 



