Abstract. — Numerical classifi- 

 cation techniques, recurrent group 

 analysis, and a clustering analysis 

 that uses the Bray-Curtis resem- 

 blance measure were used to iden- 

 tify rockfish (family Scorpaenidae) 

 assemblages in the offshore waters 

 of Oregon and Washington. Catch 

 data from six multispecies ground- 

 fish assessment surveys conducted 

 at three-year intervals (1977-92) 

 by the National Marine Fisheries 

 Service's Alaska Fisheries Science 

 Center revealed three assem- 

 blages. The first, a deep-water as- 

 semblage, consisted of shortspine 

 thornyhead, Sebastolobus alas- 

 canus, Pacific ocean perch, Seba- 

 stes alutus, darkblotched rockfish, 

 S. crameri, and splitnose rockfish, 

 S. diploproa. Redbanded rockfish, 

 S. babcocki, and rougheye rockfish, 

 S. aleutianus, were closely associ- 

 ated with this group. The second 

 assemblage consisted of canary 

 rockfish, S. pinniger, yellowtail 

 rockfish, S. flavidus, and green- 

 striped rockfish, S. elongatus. This 

 group was most abundant in areas 

 over the middle shelf. The third 

 assemblage, closely associated with 

 the second, consisted of sharpchin, 

 S. zacentrus, rosethorn, S. helvo- 

 maculatus, and redstripe, S. 

 proriger, rockfish. While the three 

 assemblages may be of particular 

 interest to ecologists, managers 

 faced with the division of the 

 Sebastes complex management 

 unit into groups that better reflect 

 rockfish cooccurrence may only be 

 able to manage the latter two as- 

 semblages as one shelf-rockfish 

 unit. 



Rockfish assemblages of the middle 

 shelf and upper slope off Oregon 

 and Washington 



Kenneth L. Weinberg 



Alaska Fisheries Science Center 



National Marine Fisheries Service, NOAA 



7600 Sand Point Way N.E., Seattle, WA981 15-0070 



Manuscript accepted 4 January 1994. 

 Fishery Bulletin 92:620-632 ( 199 I 



620 



Over the last three decades, some 

 stocks of the more than 30 species 

 of rockfish (family Scorpaenidae) 

 known to inhabit the offshore wa- 

 ters of Oregon and Washington 

 (Eschmeyer and Herald, 1983) have 

 been the target of intense foreign 

 and domestic fishing pressure in a 

 largely multispecies trawl fishery. 

 In 1982 a groundfish fishery man- 

 agement plan was implemented by 

 the Pacific Fisheries Management 

 Council to address the reductions in 

 groundfish populations, including 

 serious declines of several rockfish 

 species in some areas. This plan was 

 based on an underlying single-species 

 management philosophy. 



In both the Columbia and the 

 U.S. portion of the Vancouver (US- 

 Vancouver) management areas in- 

 stituted by the International North 

 Pacific Fisheries Commission 

 ( INPFC ), annual harvesting restric- 

 tions have been fashioned for Pacific 

 ocean perch, Sebastes alutus, widow 

 rockfish, S. entomelas, shortbelly 

 rockfish, S. jordani, and thorny- 

 heads, Sebastolobus spp. The re- 

 maining rockfish species have been 

 lumped into a single management 

 unit, the Sebastes complex. In ad- 

 dition to individual trip limits, cur- 

 rent restrictions for this large group 

 involve an overall annual harvest 

 guideline and harvest guidelines for 

 two of its already stressed compo- 

 nents, yellowtail, Sebastes flavidus, 

 and canary, S. pinniger, rockfish 

 (PFMC, 1992 1 ). While efforts to pre- 

 vent over-harvesting of yellowtail 



and canary rockfish continue, the 

 fishing pressure on the minor rock- 

 fish in the management unit has 

 escalated. Species, such as dark- 

 blotched rockfish, S. crameri, are 

 becoming increasingly important to 

 fishermen. 



This research stems from a con- 

 cern over the long-term effects of the 

 trawl fishery on the condition of the 

 rockfish community as a whole. 

 Current reductions in some stocks 

 along with present bycatch prac- 

 tices may precipitate the need for 

 changes in management policies to 

 conserve these stocks. One possible 

 course of action involves multi- 

 species management, whereby cooc- 

 curring species are managed as a 

 species complex or assemblage. If 

 needed, restrictions could be placed 

 on the fishery for the assemblage 

 when specific components become 

 stressed. An effective assemblage 

 management program requires 

 knowledge of interspecific associa- 

 tions in addition to individual life 

 histories, distribution, and abun- 

 dance patterns. 



Prior knowledge of offshore rock- 

 fish associations has largely been 

 inferred from shoreside sampling of 

 commercial catches. In recent years 

 several investigations have been 



1 Pacific Fishery Management Council 

 l PFMC I. 1992. Status of the Pacific coast 

 groundfish fishery through 1992 and rec- 

 ommended acceptahle biological catches 

 for 1993; stock assessment and fishery 

 evaluation. Pacific Fishery Management 

 Council, Metro Center, Suite 420, 2000 SW 

 First Ave., Portland, OR 97201, 80 p. 



