Yoklavich et al : Habitat associations of deep-water rockfishes 



635 



lated site 5 had the lowest diversity among 

 all sites and depths, as measured by H' 

 and J'. 



Discussion 



Habitats 



Several studies have described distinct 

 fish-habitat associations for various spe- 

 cies of benthic rockfishes during different 

 stages of development ( Carlson and Straty, 

 1981; Pearcy et al., 1989; Carr, 1991; Stein 

 et al.. 1992; O'Connell and Carlile, 1993). 

 Although species composition may vary 

 latitudinally, there is remarkable concor- 

 dance between some of the habitat guilds 

 identified in Soquel Canyon and the results 

 of a habitat-based assessment of fishes 

 using similar techniques and habitat char- 

 acterizations on Heceta Bank off central 

 Oregon (Stein et al., 1992). Mud, rock- 

 boulder, and boulder habitats were most 

 distinct in both studies and included the 

 same dominant species; M. pacificiis. S. 

 alascanus, and Agonidae were abundant 

 on mud. whereas S. wilsoni was the single 

 most abundant species in the rock-boul- 

 der habitat of Soquel Canyon and the boul- 

 der habitat on Heceta Bank (Table 2). 

 Fish assemblages in low relief, mixed hab- 

 itats of mud, cobble, and pebble grouped 

 together, and although dominant species 

 were largely different (i.e. mud-cobble hab- 

 itat dominated by S. zacentrus and S. 

 wilsoni in Oregon and by S. saxicola. S. 

 helvomaculatus and Agonidae in Soquel 

 Canyon), the assemblages were made up 

 of relatively small species in both studies. 

 Several species common to both studies 

 were characterized similarly in terms of 

 habitats (e.g. associations of S. pinniger 

 with rock-boulder combinations and S. 

 elongatus with mud-cobble combinations). 



Several of the species-habitat associations identified 

 in Soquel Canyon also agreed with those described even 

 farther north. From submersible observations off British 

 Columbia, albeit made at shallower depths (21-150 m) 

 and with less comprehensive habitat classifications than 

 in Soquel Canyon or Heceta Bank, Murie et al. ( 1994) and 

 Richards (1986) reported adult S. ruherrimus to be found 

 exclusively on complex rock habitats, whereas S. elonga- 

 tus was almost exclusively associated with sand-mud and 

 mud-cobble substrata of low relief In the eastern Gulf 

 of Alaska, adult S. rubernmus were found to be strongly 

 associated with boulder fields, broken rock, overhangs, and 

 crevices (O'Connell and Carlile, 1993), features similar 

 to those of habitats described for this species in Soquel 

 Canyon. 



Shallow Deep 



50n Sebastes chlorostictus 



Shallow Deep 



Sebastes helvomaculatus 



Sebastes elongatus 



Sebastes saxicola 



252 



Figure 7 



Mean size (vertical bars are 1 standard error) for dominant species in shal- 

 low and deep depth categories over all bottom types at study sites 1 to 3 and 

 .5. Small numbers above bars are sample sizes. 



The generalities in habitat-specific associations, such as 

 those described above for several rockfish species occur- 

 ring along the entire west coast of the United States from 

 central California to Alaska, can be valuable in predict- 

 ing community structure and its response to perturbation. 

 Identifying functional groups or habitat guilds that persist 

 coastwide will be especially useful when applying these 

 small-scale relationships between species and habitats 

 to broader-scale resource surveys, potentially improving 

 assessments of groundfish populations. Additionally, estab- 

 lishing these groups is critical to incorporating the con- 

 cept of essential groundfish habitats, and negative impacts 

 to them into the management of fisheries in relatively 

 deep water, as required by the Sustainable Fisheries Act 

 of 1996. 



