320 



Fishery Bulletin 92|2), 1994 



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of bathymetry or habitat surveyed from 

 the submersible. Yellowtail rockfish may 

 be segregated spatially from tiger rock- 

 fish and, to some degree, copper and 

 quillback rockfish, because the activities 

 of yellowtail rockfish consistently placed 

 them in the water column near the sub- 

 strate but never in direct contact with 

 the bottom. The appearance of quillback 

 and copper rockfish near to one another 

 (Fig. 6) was consistent with observations 

 from SCUBA dive surveys at Saanich 

 Inlet in 20-40 m. Sympatric aggrega- 

 tions of quillback and copper rockfish 

 over complex habitat in Saanich Inlet 

 can be dense (-25-50 fishlOOm" 2 ) 

 (Murie, 1991). 



Published information on in situ be- 

 havioral activity, species associations, 

 and density of tiger rockfish is scarce, no 

 doubt in part due to the consistently low 

 densities in which this species is encoun- 

 tered. Tiger rockfish have been observed 

 in low densities, and primarily as only 

 a single fish encountered at any one 

 time, in waters <30 m deep in Puget 

 Sound (Moulton, 1977), in 21-140 m in 

 the northeastern Strait of Georgia 

 (Richards and Cass, 1985), in 64-305 m 

 depths off Oregon (Pearcy et al., 1989), 

 and in <30 m in Saanich Inlet (Murie, 

 1991). As 21% (6/28) of S. nigrocinctus were observed 

 within 3 m of another tiger rockfish in our study 

 (Fig. 6), this species may not be as 'solitary' as in- 

 dicated by the previous studies. Density of tiger 

 rockfish may be limited by the availability and de- 

 fense of suitably large shelter holes, which the fish 

 retreat into upon approach by a SCUBA diver 

 (Murie, pers. obs.). 



The depth distribution of rockfish in Saanich In- 

 let, and hence any size or species associations, may 

 be influenced by a number of factors, including a) 

 the physical regime of the inlet; b) the paucity of 

 observations for relatively uncommon species; and 

 c) the actual depth range and total number of 

 transects surveyed with the submersible. The year- 

 round oxygen deficiency in waters >100 m in 

 Saanich Inlet, and the intermittent anoxia that oc- 

 curs in waters of 125-234 m depth during January 

 to August (Liu, 1989), may act to compress or shift 

 the depth distribution of rockfish compared to open 

 coastal waters where relatively deep water is not 

 limiting in dissolved oxygen. In Saanich Inlet, squat 

 lobsters, Munida quadrispina, migrate vertically en 

 masse to avoid decreasing oxygen levels (Burd, 



QUILLBACK (n=681) 





1 



COPPER (n=24) 



1 

 11 



-2 



Wwft . 



rrrvrrx 



TIGER (n=28) 



L 



m 



4T77T . . JZZ3, 



T YT YE GS A 



YELLOWTAIL (n=23) 



I 



\ rrr\n-r- il 





rrr\ 



Q C T YT YE GS A 



SPECIES 



Figure 6 



Percent occurrence of conspecific and heterospecific rockfish in as- 

 sociation with quillback rockfish, Sebastes maliger; copper rockfish, 

 S. caurinus; tiger rockfish, S. nigrocinctus; and yellowtail rockfish, 

 S. flavidus; Species key: Quillback rockfish (Q), copper rockfish (C), 

 tiger rockfish (T), yellowtail rockfish (YT), yelloweye rockfish (YE), 

 greenstriped rockfish (GS), and alone (A). 



1983) although catastrophic mortality of spot 

 prawns, Pandalus platyceros, in 85—90 m depth has 

 been attributed to a sudden intrusion of displaced 

 anoxic bottom-water into midwater depths 

 (Jamieson and Pikitch, 1988). For mobile organisms 

 (such as rockfish) decreasing oxygen levels may 

 elicit a behavioral response involving a vertical or 

 horizontal habitat shift (Kramer, 1987). Of three 

 transects in Saanich Inlet that started at 150 m, no 

 rockfish were observed at depths >115 m, and only 

 three quillback rockfish were seen at depths >100 

 m (note: one of these transects was not used in the 

 overall analysis owing to loss of the audio-track at 

 <80 m). With the exception of copper rockfish, Hart 

 (1973) reports maximum depths of >250 m for the 

 other rockfish species. In addition, quillback, tiger, 

 greenstriped, and yellowtail rockfish have been ob- 

 served from submersibles at depths >120 m 

 (Richards and Cass, 1985; Pearcy et al., 1989). 



The scarcity of observations on relatively low den- 

 sity species of rockfish, especially in combination 

 with time limitations of the submersible, could also 

 affect our interpretation of rockfish depth distribu- 

 tion. In Saanich Inlet, few rockfish other than quill- 



