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



843 



m, and there was some indication of a secondary increase 

 in diversity at 150 m for the most southerly latitudes 

 34.0-36.0°N (Fig. 41. The distribution of species richness 

 indicated that the existence of a distinct ridge at depths 

 of 200-250 m — the highest portion of the ridge occurring 

 between 36.0 and 39.0°N latitude (Fig. 5). In that region, 

 in excess of eight distinct species co-occurred in individual 

 trawl samples. A solitary peak in richness occurred at a 

 depth of 500 m near 37.5°N latitude (Fig. 5). Inspection 

 of the raw data revealed that this peak was heavily influ- 

 enced by a single trawl sample, but there was no indica- 

 tion of a data recording error in this sample. 



The spatial distribution of CPUE for each of the rockfish 

 species is shown in Figures 6-10. The particular sequence 

 of species in these figures corresponded to clustering re- 

 sults that are presented below. Careful examination of 

 these 26 distributions revealed that the depth distribu- 

 tions of almost all species were not related to latitude. 

 The sole exception to this generalization was the depth 

 distribution for shortspine thornyhead, which showed a 



significant interaction between depth of capture and lati- 

 tude, based on results from a two-way factorial ANOVA. 

 For that species, depth distribution shifts into deep water 

 at more southerly latitudes (Fig. 6). 



Latitudinal boundaries of rockfish distributions ap- 

 peared to be influenced by two of the main bathymetric 

 features on the U.S. west coast. In particular, the Men- 

 docino Escarpment (ME), located at approximately 40.4°N 

 latitude, and Monterey Canyon (MC), located near 36.8°N 

 latitude, appear to form distributional impediments for 

 some of the species, and other species appeared to be dis- 

 tributed more uniformly across the entire latitudinal range 

 of the study (Figs. 1, 6-10). Examples of species whose 

 distributional boundaries appeared to be influenced by 

 the ME were blackgill rockfish (S. melanostomus), Pacific 

 ocean perch, chilipepper (S. goodei), shortbelly rockfish 

 iS. jordani), bocaccio, and greenspotted rockfish. Species 

 whose distributions appeared to border on MC were dark- 

 blotched, greenstriped, canary, yellowtail, widow, sharp- 

 chin, and rosethorn rockfish (Figs. 6-10). 



