Williams and Ralston: Distribution and co occurrence of Sebastidae off California and Oregon 



837 



of California consists primarily of sampling commercial 

 and recreational landinKs at ports, and for these landings 

 there is little information on catch location (Pearson and 

 Erwin, 1997; Sampson and Crone, 1997). The National 

 Marine Fisheries Sci-vice, Alaska Fisheries Science Cen- 

 ter (AFSC) westcoast triennial continental shelf bot- 

 tom-trawl survey, which enters into California waters, 

 has yielded useful spatial information for determining 

 groundfish distributions and co-occurrences. This survey 

 began in 1977 as a rockfish survey but changed focus in 

 subsequent years, depending on the particular informa- 

 tion needs at the time (Dark and Wilkins, 1994; Wilkins 

 et al., 1998). For the eight surveys conducted from 1977 to 

 1998, the shelf trawl survey covered the area from central 

 V'ancouver Island, British Columbia, to Point Conception, 

 California, at depths ranging from 50 to 500 m (Wilkins 

 etal.. 1998). 



Along the U.S. west coast, 60-65'7i^ of the groundfish 

 catch (exclusive of Pacific whiting) is taken off the coasts 

 of Washington and Oregon (PFMC-). This area has been 

 the focus of past studies examining groundfish popula- 

 tion distributions and assemblages (e.g. Gabriel and 

 Tyler, 1980; Leaman and Nagtegaal, 1986; Rickey and 

 Lai, 1990; Rogers and Pikitch, 1992; Weinberg, 1994; 

 Jay, 1996; Gunderson, 1997). In these previous studies 

 of rockfish distributions and groupings, rockfish could 

 be broken into shelf and slope assemblages (e.g. Rogers 

 and Pikitch, 1992; Weinberg, 1994). These studies have 

 all indicated that along the Oregon-Washington coast a 

 "slope" or deep-water rockfish assemblage e.xists, consist- 

 ing of darkblotched rockfish. Pacific ocean perch, splitnose 

 rockfish (S. diploproa), yellowmouth rockfish (S. reedi), 

 and shortspine thornyhead iSebastolohus alascanus). In 

 addition, a "shelf" or bottom rockfish assemblage consists 

 of yellowtail rockfish iS. flavidus), canary rockfish (S. 

 pinniger), sharpchin rockfish (S. zacentrus), greenstriped 

 rockfish (S. elongatus), rosethorn rockfish (S. helvomaciila- 

 tus), and redstripe rockfish (S. proriger). Weinberg (1994) 

 also examined patterns in abundance and number of rock- 

 fish species with respect to depth gradients. Both abun- 

 dance and the number of species increased with depth to a 

 maximum in the range of 151-250 m but both quantities 

 decreased at depths greater than 250 m. 



Groundfish assemblages off California have not been 

 studied, primarily because of the absence of detailed 

 at-sea fishery data collection programs and because of 

 smaller landings. Although California landings account 

 for only 35'^7f of the nonwhiting groundfish total (PFMC-), 

 nearly AV/c of west coast rockfish landings are taken in 

 California waters (Herrick et al.'). Thus, an understand- 

 ing of the distribution and co-occurrence of rockfishes off 

 the California coast would help with efforts to implement 

 effective fishery management actions leading to a sus- 



'■^ PFMC (Pacific Fishery Management Council). 2000. Status 

 of the Pacific Coast groundfish fishery through 2000 and 

 recommended acceptable biological catches for 2001 — stock 

 assessment and fisherv* evaluation. Pacific Fishery Manage- 

 ment Council. 2130 SW Fifth Ave., Suite 224. Portland. Oregon 

 97201. 



48 



46 



42 



40 



38 



36 



34 



Vancouver 



Washington 



Columbia 



Oregon 



Eureka 



Cape Blanco 



\ 



N 



■"Cape Mendocino 



I California 



Monterey 



^fean Franc 



isco Bay 

 Monterey Bay 



Conception 



'_Pl Buchon 

 l^Pl-Conception 



-132 -130 128 -126 -124 -122 -120 -118 -116 -114 

 Longitude 



Figure 1 



Map of the west coast of the United States, including names 

 of important coastal features and International North Pacific 

 Fisheries Commission management areas. 



tainable California rockfish fishery. In particular, an un- 

 derstanding of rockfish distributions and co-occurrences 

 could lead to improved definitions of species complexes. 

 Weinberg ( 1994) analyzed rockfish assemblages of the "Co- 

 lumbia" and U.S. portion of the "Vancouver" fishery man- 

 agement areas, as specified by the International North 

 Pacific Fisheries Commission (INPFC) (Fig. 1). In part to 

 complement Weinberg's (1994) analysis, we analyzed the 

 AFSC continental shelf trawl survey data from the more 

 southerly waters of the Eureka, Monterey, and Concep- 

 tion INPFC areas, i.e. all sampling conducted south of lat. 

 43°N(Fig. 1). 



Materials and methods 



Rockfish likely form aggregations or complexes as a 

 response to oceanographic and bathymetric features. For 

 this reason the bathymetry of the region encompassed by 

 the limits of the survey area in the Eureka, Monterey, and 

 Conception INPFC areas was characterized. The study 

 area is the area of marine waters located from lat. 34° 

 to 43°N within a depth range of 50-500 m. Bathymetric 

 data for this region were obtained from the National 

 Ocean Service Hydrographic Data Base (NOSHDB). The 



