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Fishery Bulletin 91(2), 1993 



Density estimates were obtained for combinations of 

 species, area, depth, and habitat type using the den- 

 sity estimator advanced by Burnham et al. (1980), ex- 

 cept that length of transect (1,) as used in the denomi- 

 nator was not doubled, since we were able to count 

 fishes only on one side of each line transect. Data from 

 all transects were combined, and yelloweye rockfish 

 density was estimated as 



Dy E 



nf(0) 



where n = total yelloweye rockfish adults observed 

 (from all transects), and L = total line length (all 

 transects combined) in meters. 



We used the indirect method of estimating variance 

 in density (Burnham et al. 1980:54), and f(0) was esti- 

 mated from detection functions based on the hazard- 

 rate perpendicular distance model of Hayes & Buckland 

 (1983). 



Results 



Density estimates 



No discernable difference was noted in the occurrence 

 of yelloweye rockfish between day and night replicate 

 transects, and all density estimates are calculated from 

 daytime dives. Estimated densities of yelloweye rock- 

 fish in 1990 and 1991 varied from 1954/knr to 2531/ 

 km 2 (Table 1). Estimated probability density functions 

 (pdf) generally exhibited the "shoulder" (i.e., an inflec- 

 tion and asymptote in the pdf for perpendicular dis- 

 tances near 0) that Burnham et al. ( 1980) discuss as a 

 desirable attribute of the pdf for estimation of f(0) 

 (Fig. 2). 



Habitat effects 



Boulder fields were the most densely populated 

 habitat type, followed by broken rock (Table 2). 

 Although density was greater in boulder cover regions, 



the occurrence of this habitat type was relatively in- 

 frequent, accounting for only 16% of the total bottom 

 surveyed. 



Surveyed habitat ranged from low-relief mud to 

 high-relief pinnacles and cliff faces. The predominant 

 rock type was volcanic, including folded lava flats and 

 columnar basalt. Adult yelloweye rockfish were en- 

 countered over all habitats surveyed, but occurred 

 most frequently over broken rock and boulder fields, 

 often observed resting in refuge spaces such as cracks, 

 caves, or overhangs (Fig. 3). They were also observed 

 hovering off cliff faces above cobble or pavement bot- 

 toms. Generally, only one yelloweye rockfish was ob- 

 served per refuge space, but often the hole was co- 

 occupied by a tiger rockfish Sebastes nigrocinctus. 

 Frequency-of-occurrence of yelloweye rockfish over 

 soft, cobble, and continuous rock bottom was too low 

 to provide acceptable line-transect density estimates. 

 In both the Sitka Sound and Fairweather areas, there 

 are infrequent abrupt pinnacles overlaid with mas- 

 sive boulders and overhangs. Density of yelloweye 

 and other species was extremely high in these habi- 

 tats. In the Sitka area we surveyed two adjacent 

 pinnacles: one pinnacle highly dissected with many 

 boulders and overhangs, the other comparatively 

 smooth. Occurrence of yelloweye rockfish on the com- 

 plex habitat pinnacle was clearly higher than on the 

 smoother pinnacle. Alhough gross vertical relief is 

 similar between the two pinnacles, the number of 

 refuge spaces differed and appeared to be important 

 in the occurrence of yelloweye rockfish. 



Depth effects 



Depth effects on abundance were difficult to interpret 

 because of the confounding influence of habitat. Depth- 

 related density differences were evaluated by combin- 

 ing the 1990 and 1991 Sitka data and examining two 

 depth zones within the two preferred habitat 

 types: broken rock and boulder. In both habitats, deep 

 zones had higher abundances than shallow zones 

 within the same habitat type. Boulder areas differed 

 the most between shallow and deep zones: The high- 

 est estimated density in boulder areas was in 

 the deep zone where 9135 yelloweye rockfish/ 

 km 2 were counted, compared with 6122 yelloweye 

 rockfish/km- in the shallow zone. The deep-zone 

 broken-rock habitat had 2831 yelloweye rockfish/ 

 km 2 - compared with 2748/km 2 for the shallow 

 zone. 



Juvenile yelloweye 



Abundance of juvenile yelloweye rockfish was too 

 low to obtain reliable habitat-specific density es- 



