Matthews Habitat use by rockfishes in central Puget Sound 



237 



rockfish habitat in the summer, Hkely represent essen- 

 tial summer feeding area for rockfishes. Although den- 

 sities are low, this habitat type is widespread in Puget 

 Sound. In order to protect low-relief habitats, they 

 would obviously have to be preserved year-round, i.e.. 

 not altered or destroyed. Thus, in terms of seasonal 

 stability in densities, presence of all size categories, and 

 seasonal resource availability, I suggest the following 

 ranks for the different habitats, listed from highest to 

 lowest: High-relief rocky reefs, low-relief reefs (impor- 

 tant as summer feeding area and thus contribute to 

 year-round growth), artificial reefs (pending further 

 research and assessment), and sand/eelgrass. 



Regardless of which habitat has the highest quality, 

 the habitat types examined in this study were utilized 

 differently by the various size groups and species. 

 Recently, however, Hueckel et al. (1989) have sug- 

 gested that artificial reefs can be used as mitigation 

 for the loss of natural rocky-reef habitat. Mitigating 

 the loss of natural habitats with artificial reefs uses the 

 rationale that artificial reefs provide rocky-reef type 

 substrate that replicates natural rocky reefs. Hueckel 

 and Buckley (1989) reported that artificial reefs in 

 Puget Sound replicate processes on natural reefs and 

 provide as evidence the similarity in the number of fish 

 and prey species present on artificial and natural reefs. 

 My research indicated that rockfish species composi- 

 tion was similar (with the exception of brown rockfish) 

 between natural and artificial reefs. However, these 

 species utilize artificial reefs quite differently than 

 natural reefs: Large copper rockfish leave artificial 

 reefs during the summer, large quillback rockfish are 

 found in small numbers, and artificial reefs are domi- 

 nated by extremely high densities of small quillback 

 rockfish, unlike any natural reef I surveyed. In fact, 

 the artificial reefs I studied seem to represent an 

 anomalous habitat unlike any natural habitat. 



Furthermore, the difference in resource availability 

 and habitat use may result in different birth and death 

 rates on different habitats. Thus, the different habitats 

 could be viewed as sources, where reproductive out- 

 put exceeds deaths, or sinks, where a deficit exists 

 (Pulliam 1988). On the superficial observation of high 

 densities of quillback rockfishes on artificial reefs, it 

 could be determined that the destruction of a nearby 

 rocky reef would have little impact on rockfishes. 

 Pulliam (1988) points out that if a habitat (e.g., artificial 

 reef) being preserved was a sink and the one being 

 destroyed was a source (e.g., natural rocky reef), 

 destruction of a relatively small source habitat could 

 then have disastrous results. For example, if a low- 

 relief natural reef was destroyed for a development 

 project, the loss of the productive feeding area used 

 by artificial-reef rockfishes during the summer could 

 result in reduced growth and less reproductive output. 



Again, whether or not artificial reefs provide adequate 

 food for such high densities of rockfishes is unknown. 

 The largest rockfish inhabiting artificial reefs were 

 those that made use of natural habitats; their move- 

 ment was confirmed in a tagging study (Matthews 

 1988). Thus copper rockfish may be maintained by a 

 source habitat when they make use of kelp beds dur- 

 ing the summer. In addition, artificial reefs are con- 

 siderably smaller than natural reefs, so they would not 

 compensate for the total loss of abundance (Ambrose 

 and Swarbrick 1989). Thus it is premature and specu- 

 lative to suggest that artificial reefs should be used as 

 mitigation. 



Summary 



Habitat surveys comparing monthly densities of cop- 

 per, quillback, and brown rockfishes on high-relief 

 rocky reefs, low-relief rocky reefs, high-relief artificial 

 reefs, and sand/eelgi'ass areas demonstrated strong dif- 

 ferences in how rockfishes utilize these habitats. High- 

 relief rocky reefs had the most consistent densities of 

 the three species of rockfishes, mostly fish >200 mm. 

 Low-relief rocky reefs were primarily inhabited in the 

 summer months coincident with the summer growth 

 of Nereocystis leutkeana. YOY rockfishes were also 

 observed on low-relief reefs; however, most fish left 

 these reefs in the fall. The highest densities of rock- 

 fishes, primarily 80-200 mm quillback rockfish (up to 

 420/90-m'^ transect), were observed on artificial reefs 

 and high densities of large copper rockfish were also 

 observed. On artificial reefs, density fluctuations were 

 dramatic; copper rockfish densities peaked in the fall 

 and winter and declined (to 0/transect) during the sum- 

 mer and quillback rockfish densities also seasonally 

 fluctuated. Brown rockfish were rarely seen on the 

 artificial reefs. Sand/eelgrass areas were the least util- 

 ized habitat type; only during July and August were 

 YOY, adult copper rockfish, and brown rockfish ob- 

 served on one sand/eelgrass habitat. Although all four 

 habitats were used, natural reefs may represent source 

 habitats that are used by and maintain rockfishes on 

 less productive sink (artificial reef) habitats. Thus the 

 recent use of artificial reefs as mitigation for the loss 

 of natural reefs could have negative impacts on rockfish 

 populations. 



Acknowledgments 



I am grateful to the many people who helped me com- 

 plete this study, which was part of my dissertation 

 research at the University of Washington School of 

 Fisheries. I was fortunate to have the expert diving 

 assistance of Robert Reavis throughout the entire 



