Love et al : Fish assemblages around oil platforms in the Santa Barbara Channel area 



105 



similar assemblages were on platforms near the geo- 

 graphic extremes (Hidalgo and Grace). 



Density and biomass of all species combined also 

 varied among rigs but in a pattern different from 

 species richness and diversity (Fig. 5B). However, 

 similar to richness and diversity, density and bio- 

 mass differences could not be explained by bottom 

 depth or by geography (linear regression; density vs. 

 depth, r-=0.22, P=0.35, biomass vs. depth, 7-2=0.06, 

 P=0.64; Spearman rank correlation: density vs. ori- 

 entation, rj=-0.31, P=0.54, biomass vs. orientation, 

 r,=-0.37, P=0.46). 



Although bottom depth did not explain the pat- 

 terns of abundance of all species combined, the abun- 

 dance patterns of individual species did relate more 

 strongly to bottom depth. Among the more com- 

 monly observed species, eight showed depth-related 

 patterns of abundance (Fig. 6). Copper and vermil- 

 ion rockfishes, lingcod, and painted greenling were 

 most dense around the bottoms of some of the shal- 

 lower platforms (especially platform Irene). Half- 

 banded and flag rockfishes were most dense on the 

 bottoms of the middepth structures and bocaccio 

 and greenspotted rockfish were most common at the 

 bottom of the deeper platforms. 



Midwater habitat 



All platforms Rockfishes also dominated the mid- 

 water portions of the platforms, but were primarily 

 YOYs and slightly older juveniles. Rockfishes repre- 

 sented 91.4% of the individuals (Table 3) and 85.9% 

 of the biomass (Table 2) in the midwater. Although it 

 was difficult to identify many of the smaller individ- 

 uals, widow rockfish were by far the most common 



species, representing 35.0% of all fishes seen. It is 

 likely that many of the small, unidentifiable YOYs 

 also were widow rockfish. YOY bocaccio also were 

 fairly abundant around some of the platforms and 

 occasionally schooled with widow rockfish. Both spe- 

 cies formed relatively tight, polarized schools, loosely 

 associated with the pilings and crossbeams (Fig. 

 4F). When disturbed, the schools immediately swam 

 inward underneath the platform structure. We also 

 saw small numbers of what we tentatively identified 

 as YOYs of the complex of kelp, copper, gopher and 

 black-and-yellow rockfishes (S. chrysomelas). These 

 were found in smaller, much less coherent aggrega- 

 tions and were more likely to move in closer to the 

 substrata when disturbed. 



Painted greenling, primarily small individuals, 

 were the most commonly seen nonrockfish species. 

 We often saw solitary individuals resting on the 

 crossbeams. Other species occasionally seen near or 



