Jagielo et al ; Demersal groundfish densities in trawlable and untrawlable habitats off Washington 



557 



were Pacific ocean perch (S. alutus), splitnose rockfish 

 (S. diploproa), greenstriped rockfish, and bocaccio [S. 

 paucispinis). Major species on untrawlable bottom were 

 sharpchin (S. zacentrus) and redbanded rockfish (S. bab- 

 cocki). In a submersible study conducted off Southeast- 

 ern Alaska (188-290 m), Krieger (1993) compared the 

 fish densities of 4 untrawlable sites with 16 trawlable or 

 marginally trawlable sites, and reported that densities 

 of large (>25 cm) rockfish (a category that included Pa- 

 cific ocean perch, sharpchin rockfish, redstripe rockfish, 

 and harlequin rockfish (S. variegatus) were highest at 

 trawlable sites. In a study of shortraker (S. boreal is) and 

 rougheye (S. aleutianus ) rockfish conducted on the upper 

 continental slope off southeastern Alaska (262-365 m), 

 Krieger and Ito (1999) reported that soft substrates of 

 sand or mud usually had the greatest densities; hard 

 substrates of bedrock, cobble, or pebble had the least 

 densities; and habitats containing steep slopes and 

 numerous boulders had greater densities of rockfish 

 than habitats with gradual slopes and few boulders. 

 O'Connell and Carlile (1993) conducted a submersible 

 survey off southeastern Alaska in two depth strata; 

 shallow {<108 m) and deep (a 108 m). Yelloweye rock- 

 fish were observed in cobble, continuous rock, broken 

 rock and boulder habitats but were most abundant in 

 broken rock and boulder habitats of the deep stratum. 

 Habitat-specific studies in Oregon and California have 

 used finer scales of habitat classification to characterize 

 fish-habitat associations than our comparatively coarse 

 trawlable or untrawlable classification. In Oregon wa- 

 ters. Stein et al. ( 1992) reported estimates offish density 

 by habitat-type from a submersible study of six stations 

 at Heceta Bank in waters ranging from 60 to 340 m 

 in depth. Rockfishes, particularly pygmy (S. wilsoni), 

 sharpchin, rosethorn, and yellowtail, dominated all 

 substrates except mud, where Dover sole and black- 

 belly eelpouts (Lycodes pacificus) were most abundant. 

 In California waters, Yoklavich et al. (2000) conducted 

 a submersible study at Soquel canyon (94-305 m) in 

 Monterey Bay. Cluster analysis grouped fish densities 

 into six habitat guilds; most distinct were 1 ) guild I (fish 

 associated with uniform mud bottom of flat or low relief, 

 dominated by stripetail rockfish (S. saxicola)) and guild 

 VI (fish associated with rock-boulder habitat of low to 

 high relief dominated by pygmy rockfish). 



To contrast our results in Washington with findings 

 from Oregon and California, we summarized the fish 

 density estimates reported by Stein et al. ( 1992 ) and Yokla- 

 vich et al. (2000) into a format roughly comparable to our 

 data. Differences in the objectives and methods of their 

 studies precluded a rigorous quantitative comparison with 

 our results, particularly because of differences in habitat 

 classification and survey design (random sampling in our 

 study, purposive sampling in the other two studies). How- 

 ever, some interesting similarities are apparent if the most 

 highly rugose habitats of these two studies are treated as a 

 proxy for untrawlable habitat and if the low bottom relief 

 habitats are treated as a proxy for trawlable habitat (Table 

 11). Seven species (italicized in Table 1 1 ) co-occurred in all 

 three studies. For all three studies, greenstriped rockfish 



Roc)<flsh 



0.5 1 1.5 



Flatfish 



Empirical 

 Asymptotic 



2.5 



0.5 



1.5 



LIngcod 



25 



0.5 1 1.5 2 



Yelloweye rockfish 



2.5 



Tiger rockfish 



0.5 1 15 2 



Effect size index (d) 



2.5 



Figure 4 



Comparison of empirical power (from bootstrap simulation 

 results) with power calculated by using Equation 1 under the 

 assumption of asymptotic normality (a=0.05, n=8) for rockfish 

 and flatfish in the aggregate and for lingcod, yelloweye rockfish, 

 and tiger rockfish individually. 



and Dover sole densities were higher in the trawlable habi- 

 tat, and rosethorn, yelloweye and yellowtail rockfish dens- 

 ites were higher in the untrawlable habitat. Results were 

 mixed for canary rockfish (more abundant in trawlable 

 habitat in Washington but more abundant in untrawlable 

 habitat in the Oregon and California studies) and lingcod 

 (more abundant in trawlable habitat in Oregon but more 

 abundant in untrawlable habitat in the Washington and 

 California studies). 



The most striking contrast among the three studies was 

 the much lower overall magnitude of the fish densities in 

 Washington compared to Oregon and California. One pos- 

 sible explanation for this difference could be due to the 



