176 



Fishery Bulletin 105(2) 



Patch use 

 A S. semicinctus 



Patch selectivity 



Microhabitat 

 use 



B S. chlorostictus 



^^^tS"T^ 



1° Substratum 

 ^Rocl< 

 m^i Boulders 

 ED Cobbles 



Sand 



IVIud 



C S. elongatus 



I 

 I 







I 



B C S 



Patch type 



100% 



50% 



0% 

 1 00% 



50% 



0% 

 100% 



50% 



0% 



-40 -20 20 40 



Selectivity index 



Figure 7 



Intermediate and fine-scale habitat use by cobble-mud associates: (A) halfbanded 

 rockfish {Sebastes semicinctus), (B) greenspotted rockfish (S. chlorostictus), 

 and (C) greenstriped rockfish (S. elongates). Symbols and interpretation are 

 given in Figure 5. 



S. chlorostictus, along with other species, used habitats 

 comprising a combination of rock and mud. 



Soft substratum had the lowest habitat complexity 

 and the lowest diversity and density of fishes of all 

 three strata, although many of these species, particu- 

 larly the Pleuronectiformes, are important commer- 

 cial species. Stein et al. (1992), Yoklavich et al. (2000, 

 2002), and Jagielo et al. (2003) also recorded similar 

 demersal fish assemblages in flat mud habitats (i.e., 

 Pleuronectidae, namely M. pacificus, Glyptocephalus 

 zachirus [rex sole], and Lyopsetta exilis [slender sole]), 

 Agonidae, Sebastes saxicola [stripetail rockfish], Zo- 

 arcidae [eelpouts], and Sebastolobus spp. [thornyhead 

 species]). Although demersal fish assemblages over 

 trawlable habitats have been well documented by tra- 

 ditional fishery methods (e.g., Weinberg et al., 2002), 

 biases in catchability between strata (because trawls 

 may snag in complex habitats) mean that differences 



in fish assemblage structure between soft, mixed, and 

 hard strata have been difficult to identify. Although in 

 situ submersible surveys facilitate these types of com- 

 parisons, some biases may still be present. For example, 

 soft-sediment habitats reported in submersible studies 

 (e.g., Stein et al., 1992; O'Connell and Carlile, 1993; 

 Yoklavich et al., 2002) are often adjacent to, at the 

 base of, or in the general vicinity of rock outcrops. As a 

 result, it is unclear how the proximity of hard structure 

 influences demersal fish composition and abundance, or 

 whether these habitats are representative of soft-sedi- 

 ment areas where rock outcrops are not present. The 

 analysis of submersible transects in relation to distance 

 from rocks, or alternatively trawl surveys that include 

 video or acoustic images of the benthos, may help to 

 clarify these patterns. 



All three spatial scales provided valuable informa- 

 tion on how demersal fish species use benthic habitats. 



