Stem et al,: Fish-habitat associations at edge of Oregon continental shelf 



549 



and ridge habitats at 75-lOOm depths. Canonical 

 variate scores among stations differed on the third axis 

 with respect to habitat scores, but not on fish scores. 

 With respect to habitat, stations 1 and 3, which had 

 the highest amount of sand and ridge cover (Fig. 2), 

 were significantly different from stations 2, 4, and 6 

 (Kruskal-Wallis, jd<0.01) (Fig. 6C). In contrast, with 

 respect to fish abundance, stations were highly vari- 

 able, and not significantly different among stations 

 (Kruskal-Wallis, p>0.05) (Fig. 6C). 



Discussion 



The principal objective of our study was to develop 

 methods to estimate spatial variation in fish abundance 

 on Heceta Bank. However, the high variability of bot- 

 tom types encountered required that we understand 

 the effects of bottom-type variation on fish abundance 

 and distribution. 



Fish-habitat associations 



The principal components analysis showed that stations 

 with the least variability in fish abundance among 

 replicate transects were those at stations composed of 

 rock ridge, such as the bank tops (stations 1 and 3), 

 and of mud (station 5). In contrast, high variability in 

 fish abundance among replicate transects occurred at 

 stations having combinations of mud, cobble, and 

 boulders (stations 2, 4 and 6). Moreover, canonical cor- 

 relation analysis indicated that fish assemblages asso- 

 ciated with these habitats were unique. Mud, cobble- 

 boulder, and ridge-sand habitats displayed different 

 species composition and relative abundance. 



In most sampling situations, such as use of a bottom 

 trawl or bottom-set gillnet, analysis would be limited 

 to a fish-only PCA-type appproach. Within-station 

 variability, such as that documented here, would be 

 largely unaccounted for without detailed information 

 about bottom type. In the present study, canonical cor- 

 relation analysis of fish abundance relative to bottom 

 type provided key information on a major source of 

 within-station variability. 



The ability to estimate bottom-type composition and 

 determine the relationships of species with each sub- 

 strate is a critical advantage of submersible studies. 

 In shallow water, this has been done using scuba (e.g., 

 Hixon 1980, Larson 1980, Hallacher and Roberts 1985). 

 However, there are few such studies below scuba 

 depths. In the northeastern Pacific, Carlson and Straty 

 (1981) and Straty (1987) used a submersible to study 

 habitat and nursery areas for rockfishes in southeast- 

 ern Alaska. Straty (1987) concentrated on species of 

 juvenile rockfishes and their occurrence in relation to 



-2.5 -1.5 -0.5 



CCl Fish 



O 



I 



to 

 o 

 o 



-0.8 -0.3 



CC3 Fish 



XI 



o 



X 



o 

 o 



B ^g--*- 



I 

 . A . 



-2.0 -1.0 0.0 1.0 



CC2 Fish 



Figure 6 



Average canonical variate scores for each station (± 1 SE) on 

 three canonical correlation axes (see Table 4). Canonical scores 

 for habitat indicate the relative cover of specific bottom types 

 on each axis, while scores for the fish data indicate the relative 

 abundance of specific fish on each axis. 



substrate type and relief; he did not attempt to quan- 

 tify abundances. Richards (1986) similarly investigated 

 distributions of deep rockfishes at 21-140 m and related 

 their occurrence to bottom type. Although she was able 

 to show substrate associations for three species {Sebas- 

 tes elongatus, S. maliger, and S. ruberrimus), only 

 three substrate categories were used, and abundances 

 of fishes were determined on the basis of distance of 

 maximum visibility. Nevertheless, she recognized the 

 importance of such studies and developed initial 

 methods for obtaining data on this subject. 



Abundances of species 



We know of no comparable data to that presented here 

 for fish abundances on Heceta Bank. However, similar 

 studies have been done on inshore reefs in central 

 California. Miller and Geibel (1973), using scuba tech- 



