116 



Fishery Bulletin 98(1) 



compared with 4.4 fish/100 m^ on the highest density 

 natural reeD. The reef was located on the northern 

 side of the passage between San Miguel and Santa 

 Rosa islands. The average density of bocaccio across 

 all natural reefs surveyed in 1996 was only 1.26 fish/ 

 100 m-. The large numbers of bocaccio around Gail 

 may reflect the minimal fishing pressure around this 

 platform. Fishing by recreational or commercial ves- 

 sels near platforms is generally discouraged by plat- 

 form operators. In addition, because larger fishes 

 tend to live close to or inside the platforms, they 

 are difficult to catch because the habitat close to or 

 inside the platforms eludes most fishing gear. 



We realize that the data presented in this paper 

 represent a "snapshot" in time and thus issues of 

 seasonality or interannual variation in assemblage 

 structure remain to be addressed. Longer-term sur- 

 veys of the fish fauna on two platforms in the Gulf of 

 Mexico as well as one in the Santa Barbara Channel 

 showed considerable diel and seasonal variation in 

 the number of species present (Carlisle et. al 1964; 

 Hastings et. al. 1975). In addition, monthly SCUBA 

 observations on one shallow-water platform indicate 

 that there may be large temporal changes in assem- 

 blage structure (Schroeder-). Despite this, the differ- 

 ences we observed in fish assemblages among and 

 within platforms suggest that each platform may 

 have unique characteristics. 



There has been considerable discussion regarding 

 the role of artificial structures in aggregation or 

 enhanced production of marine species (or both) 

 (Carr and Hixon, 1997). Based on this study, it 

 appears that oil platforms may serve to do both. 

 First, large adult fishes of several species were pres- 

 ent on several platforms where no juveniles of those 

 species had previously been observed, e.g. vermilion 

 rockfish. It appears that those adults may have set- 

 tled away from the platforms and migrated to them 

 at some life stage. On the other hand, several plat- 

 forms had very large numbers of very young fish 

 that presumably settled to the platforms directly 

 from the plankton, e.g. widow rockfish. If we assume 

 that some of these young fishes would not have found 

 appropriate settling habitat, then platforms, at least 

 in the short term, do play some role in enhancing pro- 

 duction. To ultimately assess the role of platforms in 

 production of reef fishes, it will be necessary to under- 

 stand the fate of the young fish settling to them. 



Acknowledgments 



We would like to thank Bob Lea, Mary Nishimoto, 

 Donna Schroeder, Rick Starr, and Mary Yoklavich, 

 all of whom were instrumental in -helping us collect 



data. We would also like to express our appreciation 

 to the crew of the RV Cavalier, Douglas Morse, Jona- 

 than Blackman, Don Chesnut, Don Tondro, Nancy 

 Stewart, Erik Kohnhorst, and the pilots of the sub- 

 mersible Delta, Chris Ijames, and Dave Slater, for 

 their very professional handling of the technical 

 aspects of this survey. Lyman Thorsteinson was, as 

 always, extremely supportive and we thank him. 

 This research was based on an information need 

 identified by the Minerals Management Service's 

 Pacific OCS Region and funded through the U. S. 

 Geological Survey Biological Resources Division's 

 National Offshore Environmental Studies Program 

 (1445-CA-0995-0386). 



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