604 



Fishery Bulletin 88(3), 1990 



as were most S. miniatus and S. rubrivinctus and 

 many S. entomelas, S. mystinus, S. paucispinis, and 

 S. serranoides. 



Discussion 



During the period sampled, the platforms were impor- 

 tant sites for the Hornet's fishing effort. They were 

 also fished by other sportfishing party vessels from 

 Ventura Harbor, about 30 km to the east, though we 

 are unsure of the total effort from these vessels. In both 

 circumstances, these structures provided the vessel 

 operators with a relatively reliable source of easily 

 caught, though generally small, fish. The ease with 

 which small rockfish were caught made the platforms 

 particularly attractive to the Hornet's operators on 

 half-day runs, when the vessels carried many inexperi- 

 enced fishermen. The platforms were also utilized when 

 fishing was poor at other locations for more desirable 

 species, such as kelp bass Paralabrax clathratus. 



We have recently (1989) discussed platform fishing 

 with current Santa Barbara party vessel operators. 

 They report that though the platforms are still fished 

 for small rockfish, kelp bass are an equal or more im- 

 portant species during summer months. This is par- 

 ticularly true of the eastern platforms, particularly 

 Houchin, Hogan, and Hope (2 km east of Hogan). 

 Though there are five platforms in this complex, only 

 these three are routinely fished. During the season's 

 peak, as many as 300-400 P. clathratus per trip are 

 caught from around a single platform. Based on tag- 

 ging studies by P. Hart (Dep. Biol. Sci., Univ. Calif., 

 Santa Barbara 93106, pers. commun., Sept. 1988), it 

 is likely that kelp bass move onto the platforms before 

 summer and leave in the fall, traveling both east and 

 west, with reported movements of as much as 32 km 

 in 6 months. 



In the study conducted between 1975 and 1978, there 

 were significant differences in both species composi- 

 tions and mean sizes between the three sites (though 

 the natural reefs were much more similar with each 

 other). Much of the differences in species composition 

 between the platforms and the natural reefs came from 

 the relative abundance of high-relief substrate-associ- 

 ated rockfish (such as S. consteUatus and S. rubrivinc- 

 tus) over the reefs and their near absence around the 

 platforms. The substrata around these structures are 

 composed of a mixture of drill cuttings and mussels 

 which have broken off the platform pilings. This does 

 not appear to be suitable habitat for many rockfish 

 species. 



On the other hand, a few substrate-associated spe- 

 cies, such as juvenile 5. auriculatus and S. pinniger, 

 were most abundant around the platforms. Sehastes 



auriculatus (both juveniles and adults) are most often 

 found associated with low relief or the sand-rock inter- 

 face, habitat most similar to that around the platforms. 

 We do not know what substrata juvenile S. pinniger 

 prefer, though its abundance around the platforms and 

 scarcity over natural reefs imply it favors habitats 

 similar to S. auriculatus. 



It is unclear why S. mystinus and particularly S. hop- 

 kinsi should be relatively uncommon around the plat- 

 forms, yet abundant on the reefs. Both species are mid- 

 water planktivores, always found in association with 

 high relief. A possibility is that both species take refuge 

 in crevices at night and that these are relatively un- 

 common on the platform pilings and cross members. 



Differences in depths between the sites were prob- 

 ably responsible for only a few of the observed differ- 

 ences in species abundances and sizes. The absence of 

 P. clathratus from the 6 Mile Reef was undoubtedly 

 due to the reef's relatively extreme depth. The 6 Mile 

 Reef is situated in 74 m, well below the 46 m maximum 

 depth of P. clathratus (Eschmeyer et al. 1983). Love 

 et al (in review) summarizing ontogenetic Sebastes 

 movements, noted that almost all species recruit to 

 waters shallower than adult depth, subsequently mov- 

 ing to deeper water as they mature. If depth were a 

 major factor in our study, we would expect to see the 

 smallest rockfish at the shallowest (4 Mile Reef) sta- 

 tion. However, while both large and small individuals 

 of many rockfish species were taken at 4 Mile Reef, 

 the mean size of most species (except for S. entomelas) 

 was actually larger than at the other two sites. 



Are the platforms we sampled aiding rockfish pro- 

 duction or do they only act as aggregators? In other 

 words, do rockfish recruit from the plankton to the plat- 

 forms or do they settle out elsewhere and later migrate 

 to these structures? Though our data is not sufficient 

 to answer the question, there is evidence that at least 

 some recruitment takes place around Santa Barbara 

 platforms. In the only detailed study of a California 

 platform, Carlisle et al. (1964) found that both 5. 

 paucispinis and S. serranoides recruited to platform 

 Hazel, located in 30 m of water, about 6 km inshore 

 of our study platforms. We believe it is likely that som.e 

 rockfish species (i.e., S. entomelas, S. mystinus, S. pau- 

 cispinis, S. pinniger, and S. serranoides) recruit to our 

 platforms, particularly in light of the large numbers of 

 small fish, most only 1-2 years old. Smaller and 

 younger fish may be present at these platforms, but 

 their small size precludes their being taken by hook- 

 and-line. 



There are several reasons that mature rockfish are 

 rare around the platforms. While juveniles of deep- 

 water species (i.e., S. entomelas, S. pinniger, S. pau- 

 cispinis) are able to tolerate the warm shallow waters 

 around these structures, the adults are not (Love et al., 



