O'Connell and Carlile. Density of adult Sebastes rubernums in eastern Gulf of Alaska 



307 



1.67 3.34 5.01 6. 48 8.35 



perpendicular distance (m) 



Figure 2 



Representative probability density function Ipdfl and histogram of relative frequencies 

 (n,/(A,n)) of yelloweye rockfish observed for 5 distance intervals over boulder habitat in 

 the Sitka study area. 1990. For relative frequencies, n, = number of fish observed in 

 interval i, A, = size of class interval (in this case. 1.67ml, and n = total number of 

 yelloweye observed I in this case, 176). 



timates; hence they varied considerably (Table 3). Data 

 on frequency-of-occurrence/meter traversed suggested 

 preference by juvenile yelloweye rockfish for the shal- 

 low-zone broken-rock habitat. 



Discussion 



In addition to confirming the strong association of 

 yelloweye rockfish with rocky habitat noted by Richards 

 (1986), we were able to estimate overall and habitat- 

 specific densities for yelloweye rockfish. The only pre- 

 viously published estimates of yelloweye rockfish den- 

 sities are from the Strait of Georgia, British Columbia. 

 Richards (1986) used strip transects conducted from 

 the submersible Pisces VI to describe spatial distribu- 

 tion patterns of rockfish. Although our results were 



not directly comparable to hers 

 because of differences in habitat 

 categorization and because juve- 

 nile yelloweye rockfish were in- 

 cluded in her density estimates, 

 our results were similar. For 

 two depth categories, 21-80 m 

 and 81-140 m, Richards (1986) 

 estimated yelloweye rockfish 

 densities of -10,000 and 14,000 

 yelloweye/km 2 in her complex 

 habitat category, including high- 

 relief areas of cobble with large 

 rock, broken rock, and boulder, a 

 category that may encompass our 

 broken-rock and boulder habitat 

 types. In our study, estimated 

 densities in boulder and broken- 

 rock habitats varied from 2405 

 to 9135 yelloweye rockfish/km- 

 depending on depth. Comparison 

 of estimated densities from 

 roughly similar habitat types in 

 the two studies suggests that 

 yelloweye densities in the Strait of Georgia, BC were 

 greater than we estimated for the coast of southeast 

 Alaska. 



Use of the submersible allowed collection of qualita- 

 tive data for assessment of factors contributing to the 

 distribution and abundance of fishes. Occurrence of 

 refuge spaces may be one key to the presence of 

 yelloweye rockfish, which were normally in areas where 

 refuge spaces were available, even if the surrounding 

 habitat was not the preferred habitat of boulder or 

 broken rock. For example, we often encountered 

 yelloweye rockfish under overhangs of large, solitary 

 boulders in cobble flats. Continuous rock bottom was 

 not particularly good habitat in terms of yelloweye 

 density. Additional transects will be needed to increase 

 the precision of habitat-specific estimates and narrow 

 the associated confidence limits. Further refinement of 

 habitat categories (e.g., subcat- 

 egories of boulders based on av- 

 erage size of boulders and/or in- 

 terstitial spaces) may also yield 

 more precise habitat-specific es- 

 timates for yelloweye. 



Differences in density esti- 

 mates for juvenile yelloweye be- 

 tween the Fairweather and Sitka 

 sites are interesting. The higher 

 density on the Fairweather site 

 may be due to terrain: the Fair- 

 weather Ground is a well-defined 

 bank surrounded by large ex- 



