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



115 



young that do not disperse widely, making it unlikely 

 that they commonly find their way to platforms. 

 Kelp bass and opaleye produce pelagic larvae and 

 although it is likely that some may settle to the plat- 

 forms, conditions at these structures may preclude 

 their survival after settlement. Young opaleye seem 

 to require quiet intertidal waters and kelp bass YOY 

 may need algae or thick benthic turf to avoid preda- 

 tion (Carr, 1994; Stephens'*). Both of these conditions 

 are lacking at platforms. Moreover, in the study area 

 kelp bass recruitment is only sporadic and may not 

 have occurred in the recent past. Thus, strong cur- 

 rents and lack of suitable habitat around platforms 

 may reduce the amount of successful recruitment of 

 these and other nearshore species. 



A few species, notably painted greenling, do seem 

 to be well adapted to a substrate-associated life in 

 the midwaters. Judging from the very small individ- 

 uals we observed, it is likely that lai-vae of this spe- 

 cies recruit directly to the platform and settle out in 

 the shallower portions. We saw a wide range of sizes, 

 from newly settled individuals to adults, sitting on 

 the crossbeams and hanging vertically on the pil- 

 ings. Other than painted greenling, only a few juve- 

 nile flag, greenspotted, copper, swordspine, gopher, 

 and rosy rockfishes were seen sitting on the platform 

 in midwater. 



Although juvenile rockfishes dominated the plat- 

 form midwater, for some species platform bottoms 

 tended to harbor a wider range of life stages. For 

 some rockfishes (such as copper and greenspotted 

 rockfishes), the entire range of stages from YOY to 

 adults were present. In these species, the smaller 

 individuals tended to live somewhat away from the 

 legs and crossbeams and more among those parts 

 of the mussel shell mounds a few meters from the 

 platform. Although juvenile vermilion rockfish were 

 common on several of the shallower platforms, we 

 saw no YOYs around any of these structures. Ver- 

 milion rockfish tend to settle out in the nearshore, 

 relatively shallow waters, and it is likely that even 

 the shallowest of the surveyed platforms were situ- 

 ated in waters too deep for successful recruitment. 

 This supposition was born out in our SCUBA diver 

 surveys of platform Gina, located off Port Huen- 

 eme, southern California. Platform Gina is located 

 in waters about 33 m deep. Divers have surveyed 

 the entire structure and on several occasions have 

 noted YOY verm.ilion rockfish at the bottom of the 

 platform. 



The situation with lingcod is particularly interest- 

 ing. Including observations from all platforms, we 



observed all life stages from YOYs to large adults. 

 However, almost all the young fish lived around plat- 

 form Irene, in relatively high densities. From the 

 lengths of these animals (Miller and Geibel, 1973), 

 we determined that these fish were either YOYs 

 or one-year-olds. We noted that most were sitting 

 in the mussel shells on the bottom slightly away 

 from the structure. In an underwater survey that 

 encompasses seven platforms and 61 natural reefs 

 in central and southern California, we have never 

 encountered juvenile lingcod densities approaching 

 the levels noted around platform Irene. Similar 

 submersible research farther north, off Big Sur- 

 Monterey (Yoklavich^) and Alaska (O'Connell^) also 

 implies that such aggregations are very rare. The 

 aggregation around Irene may also be relatively 

 stable because we saw similar high densities in the 

 subsequent 1997 survey. It is unclear what attracts 

 young lingcod to this location. A large juvenile aggre- 

 gation was noted off Big Sur on a sandy bottom cov- 

 ered with ripple marks (Yoklavich"*). Perhaps young 

 lingcod seek out substrate with at least some verti- 

 cal relief and, at Irene, mussel shell mounds provide 

 this type of relief. 



Many bottom fishes tended to be patchily distrib- 

 uted around individual platforms. This is particu- 

 larly true of the aggregating species, such as bocaccio 

 and vermilion and halfbanded rockfishes. Whether 

 this is in response to current pattern, variations in 

 platform structure, or to other parameters is not 

 clear at this point. We have also observed a ten- 

 dency for small individuals, such as halfbanded rock- 

 fish or juvenile greenspotted rockfish, to be found 

 away from larger, presumably predacious, individu- 

 als. Smaller fishes also tend to be found farther away 

 from the platform, again probably to avoid the larger 

 fishes nestled in the structure. 



Fishing pressure is intense over most of the natural 

 reefs in southern California and platforms may act 

 as refuges for rockfishes and lingcod. An example is 

 the relatively high numbers of bocaccio living around 

 platform Gail. Historically, bocaccio were very impor- 

 tant recreational and commercial fish along all of Cal- 

 ifornia and owing to a combination of over-fishing 

 and poor juvenile recruitment, their populations have 

 drastically decreased ( Ralston et al. , 1996 ). Our survey 

 of the fish assemblages of 61 natural reefs off south- 

 em and central California shows that platform Gail 

 has by far the highest density of adult bocaccio of 

 all of these sites ( 10.5 fish/100 m^ on platform Gail 



■• Stephens, J. 1997. Department of Biology, Occidental College, 

 1600 Campus Rd., Los Angeles, CA 90041. Personal commun. 



■^ Yoklavich. M. 1997. Pacific Fisheries Environmental Labora- 

 tory, National Marine Fisheries Service, 1352 Lighthouse Ave., 

 Pacific Grove, CA, 93950. Personal commun. 



'^ O'Connell, T. 1998. Alaska Department of Fish and Game, 

 304 Lake St., Rm. 103, Sitka. AK, 99835. Personal commun. 



