172 



Fishery Bulletin 105(2) 



of substratum types (n = 19), where rock and boulders 

 types were the most abundant (Fig. 3A). Mixed strata 

 also contained a variety of patch types («=10), but were 

 devoid of rock and contained higher proportions of mud 

 (Fig. 3B). Soft strata contained the fewest patch types 

 (n = 3), composed primarily of homogeneous mud, and 

 small amounts of homogeneous sand and mud-cobble 

 patch types (Fig. 3C). 



Structure of fish assemblages and 

 broad-scale fish-habitat associations 



Sixty-two species of demersal fishes (from 21 fami- 

 lies) totalling 21,184 fishes were recorded during this 

 survey. Rockfishes were the most abundant portion of the 

 demersal fish assemblage, representing 93% of all fish 

 sampled (i.e., 24 rockfish species, totalling 19,668 rock- 

 fishes). Most fishes recorded (96%) were small (TL s20 

 cm) noncommercial species, dominated by small-bodied 



OC CQ O "5 S 



CC IT DC tr q; 



Substratum patch type 



Figure 3 



Intermediate-scale habitat characteristics: substratum patch 

 composition within the three broad-scale habitat strata: (A) hard 

 stratum, (B) mixed stratum, and (C) soft stratum. Substratum 

 types recorded were R = rock, B = boulders, C = cobbles, S = sand, 

 and M=mud. The first and second letters of each patch type (e.g., 

 RR, RB, RC, to MM) represent primary (50%) and secondary 

 (20%) substratum types, respectively. 



(dwarf) rockfishes, such as S. wilsoni (n = 5857, 28% of 

 all fish sampled), S. semicinctus (halfbanded rockfish) 

 (m = 5247, 25%), and S. hopkinsi (squarespot rockfish) 

 (n=2747, 13%). In comparison, both small (TL ^20 cm) 

 and large (TL >20 cm) fishes of commercial species and 

 large noncommercial species were uncommon (462 small- 

 size commercial fish (2%); 295 large-size commercial fish 

 (1%); and 79 large-size noncommercial fish (0.4%)). 



Fish density and species richness varied between 

 the three broad-scale strata. Hard stratum had the 

 highest density of fish (1357 fishes per 1000 m^), fol- 

 lowed by mixed stratum (862 fishes per 1000 m'-^), 

 and both strata were dominated by rockfishes (90%, 

 98% respectively). Inversely, soft stratum had com- 

 paratively few fish (130 fishes per 1000 m-), domi- 

 nated by nonrockfish species (63%). Small-size fishes 

 accounted for the majority of demersal fishes within 

 hard (98% of all fish sampled), mixed (99%), and soft 

 (79%) strata. In comparison, large demersal fishes 

 (TL>20 cm) were relatively uncommon in all 

 three substrata; however, the hard stratum 

 had higher densities (27 per 1000 m^ [2% of 

 all fishes in hard substratum]) than the soft 

 (21 per 1000 m^ [16%]), or mixed (4 per 1000 

 m^ [0.5%]) strata. The mixed stratum had the 

 highest number of species (44 species), where 

 64% of the species composition comprised non- 

 rockfish species. The hard stratum had slight- 

 ly fewer species (41 species) but comprised a 

 more even mix of rockfish (54%) and nonrock- 

 fish (46%) species. Soft stratum had the few- 

 est species of all three strata (19 species), of 

 which most were nonrockfish species (74%). 

 The number of commercially important species 

 decreased as habitat complexity decreased: 

 18 commercial species (15 rockfish species) 

 were recorded from hard substratum, com- 

 pared with 16 (10 rockfish species) in mixed 

 substratum, and 11 (5 rockfish species) in soft 

 substratum. 



Assemblage composition varied between the 

 three broad-scale strata (Fig. 4). High-relief 

 outcrops (hard stratum) were characterized by 

 schools of small-bodied rockfishes (S. hopkinsi, 

 S. wilsoni, and YOY), a suite of large-bodied 

 rockfish (e.g., S. paucispinis, S. flavidus, S. 

 rubrivinctus [flag rockfish], S. rosaceus [rosy 

 rockfish], and Sebasfomus spp.), and a few non- 

 rockfish species (e.g., R. nicholsii and O. elon- 

 gatus). Low-relief outcrops (mixed stratum), in 

 contrast, were characterized by schools of the 

 small-bodied rockfish, S. semicinctus, two large- 

 bodied rockfishes (S. chlorostictus [greenspot- 

 ted rockfish] and S. elongatus [greenstriped 

 rockfish]), and a variety of nonrockfish species 

 (e.g., Citharichthys spp., Zalembius rosaceus 

 [pink seaperch], Zaniolepis spp. [combfishes], 

 Argentina sialis [Pacific argentine], and O. elon- 

 gatus). Homogeneous mud areas (soft stratum) 

 differed from high-relief and low-relief outcrops 



