236 



Fishery Bulletin 88(2). 1990 



Interestingly, I never observed YOY in bullkelp cano- 

 py. The young fish were only seen on the bottom closely 

 associated with the perennial understory macrophytes 

 Agarum, Pterygophora, and eelgrass, or closely asso- 

 ciated with rocks at AR2, which has little plant cover. 

 The YOY could have spent a short period of time in 

 the bullkelp canopy before I first saw them in my 

 surveys or they may never use the bullkelp canopy in 

 my study sites. Young rockfish may not be able to main- 

 tain position in the water column in areas with current. 



It is not surprising that YOY rockfishes were seen 

 in 1987, yet not in 1988. The numbers of first-year 

 rockfish recruits reportedly vary greatly year-to-year 

 along the coast of central and northern California (Hob- 

 son et al. 1986, Gaines and Roughgarden 1987). Studies 

 in California have documented wide fluctuations in 

 YOY recroiitment sometimes influenced by warm-water 

 years and changes in distribution after kelp removal 

 (Bodkin 1988). Temperature did not appear to be a fac- 

 tor in the absence of YOY in 1988; bottom tempera- 

 tures were similar between 1987 and 1988 (Fig. 8). In 

 addition, few YOY were observed off eastern Vancou- 

 ver Island during the same time period (summer and 

 fall 1988) (L. Richards, Pac. Biol. Sttn., Nanaimo, B.C., 

 Canada V9R 5K6, pers. commun., spring 1989). Ap- 

 parently, copper, quillback, and brown rockfish recniit- 

 ment is episodic; this has important implications to our 

 understanding of the population dynamics and manage- 

 ment of Puget Sound rockfishes. 



The most numerous aggregations of YOY were ob- 

 served on low-current reefs: HR2, AR2, and SE2. YOY 

 were never observed on the highest current reefs, HRl 

 and ARl. Possibly YOY settle out on high-current reefs 

 but lack the ability to remain on the reef and are swept 

 away by strong current. In contrast, larvae may accum- 

 ulate at sites of low current velocity. Leaman (1976) 

 collected significantly higher numbers of Sebastes 

 larvae in sheltered waters than in open, more exposed 

 channels off the west coast of Vancouver Island. 

 Similarly, Haldorson and Richards' (1987) observations 

 of YOY rockfishes on eastern Vancouver Island were 

 in low-current areas. 



Experimental design 



Because underwater transects are an effective means 

 of describing large diurnally active fish populations 

 (Brock 1954, Brock 1982), my transects were probably 

 effective for estimating abundances of adult rockfishes, 

 although I probably underestimated YOY rockfishes 

 and the very dense aggregations of 80-200 mm 

 quillback rockfish on the artificial reefs. For many size 

 categoi-ies of the three species during most seasons, 

 there were density differences between the two repli- 

 cate sites (reefs) within each habitat type. This variabil- 



ity suggests there may not be a typical rocky reef or 

 artificial reef. In most cases, though, this difference 

 was due to variability in densities and not to different 

 species present on the reef. For example, both ARl and 

 AR2 had very high densities of 80-200 mm quillback 

 rockfish, perhaps a characteristic of artificial reefs in 

 Puget Sound. High densities of 80-200 mm rockfishes 

 were not observed on any other reef type, but AR2 had 

 significantly larger densities, perhaps due to location 

 or age of the reef. 



Habitat quality 



Which is the highest quality habitat? One view of habi- 

 tat quality would predict that densities are directly pro- 

 portional to quality; rockfish densities are highest 

 where habitat quality is highest. This reasoning forms 

 the basis of many current habitat assessment models 

 in resource management (Van Home 1983). In the 

 absence of long-term information on growth, survival, 

 stability, and other features of how species respond to 

 different habitats, habitat quality is evaluated in short- 

 term studies describing densities (Van Home 1983). 

 Those habitats with the highest densities will be those 

 most important to the maintenance of that species and 

 should ultimately be protected as critical habitat. It is 

 important to note that densities can be misleading in 

 designating habitat quality (Van Home 1983). While 

 my habitat surveys documented the highest rockfish 

 densities on artificial reefs, the densities underwent 

 major fluctuations. According to classic ecological 

 theory, as density increases habitat quality declines 

 (Svardson 1949, Fretwell 1972). If resources are 

 limited, then at high rockfish densities, food, hiding, 

 and resting places would be in short supply, thereby 

 reducing growth and survival. In my study, changes 

 in availability of resources presumably were the causes 

 for rockfish density fluctuations. Therefore, a true mea- 

 sure of habitat quality should include factors other than 

 densities, such as availability of essential resources, 

 stability over time, survival, reproductive output, 

 growth, and the animal's preference for that habitat. 

 Nevertheless, copper, quillback, and brown rockfish 

 utilized all four habitat types surveyed, and each 

 habitat is important. But some of these habitats vary 

 seasonally vary their suitability, and so rockfishes move 

 to exploit alternate habitats when suitability is low 

 (Matthews In press). Thus, for rockfishes, I would 

 argue that high densities should not be the primary in- 

 dicator of habitat quality, particularly in reference to 

 the high ratio of small/large quillback rockfish on ar- 

 tificial reefs. Documenting densities of rockfishes on- 

 ly during a short time frame (few months) would not 

 be representative of that habitat's importance. In addi- 

 tion, low-relief rocky reefs, although only important as 



