542 



Abstract— Between 1995 and 2002, 

 we surveyed fish assemblages at 

 seven oil platforms off southern and 

 central California using the manned 

 research submersible Delta. At each 

 platform, there is a large horizontal 

 beam situated at or near the sea floor. 

 In some instances, shells and sedi- 

 ment have buried this beam and in 

 other instances it is partially or com- 

 pletely exposed. We found that fish 

 species responded in various ways to 

 the amount of exposure of the beam. 

 A few species, such as blackeye goby 

 iRhmogobiopts nicholsii). greenstriped 

 rockfish iSebastes elongatus), and pink 

 seaperch iZalemhius rosaceus) tended 

 to avoid the beam. However, many 

 species that typically associate with 

 natural rocky outcrops, such as bocac- 

 cio {S. paucispinis), cowcod (S. levis), 

 copper (S. cauriniis). greenblotched 

 (S. rosenblatti). pinkrose (S. simula- 

 tor) and vermilion (S. miniatus) rock- 

 fishes, were found most often where 

 the beam was exposed. In particu- 

 lar, a group of species (e.g., bocaccio, 

 cowcod, blue (Sebastes niystinus), and 

 vermilion rockfishes) called here the 

 "sheltering habitat" guild, lived pri- 

 marily where the beam was exposed 

 and formed a crevice. This work dem- 

 onstrates that the presence of shelter- 

 ing sites is important in determining 

 the species composition of man-made 

 reefs and, likely, natural reefs. This 

 research also indicates that adding 

 structures that form sheltering sites 

 in and around decommissioned plat- 

 forms will likely lead to higher densi- 

 ties of many species typical of hard 

 and complex structure. 



The relationships between fish assemblages 

 and the amount of bottom horizontal beam 

 exposed at California oil platforms: 

 fish habitat preferences at man-made platforms 

 and (by inference) at natural reefs 



Milton S. Love (contact author) 



Marine Science Institute 

 University of California 

 Santa Barbara, California, 93106 

 Email address: loveighfesci ucsbedu 



Anne York 



PO 31375 



Seattle, Washington 98103 



Manuscript submitted 6 October 2004 

 to the Scientific Editor. 



Manuscript approved for publication 



14 December 2005 by the Scientific Editor. 



Fish. Bull. 104:542-549 (20061. 



Understanding the habitat preferences 

 of deeper-water (below scuba depth) 

 fishes has proven to be elusive. Off the 

 Pacific Coast, several studies (Stein 

 et al., 1992; Yoklavich et al., 2000; 

 Nasby-Lucas et al., 2002) have dem- 

 onstrated that habitat characteristics 

 play a major role in shaping deeper- 

 water fish assemblages. In those stud- 

 ies it was apparent that, although 

 individuals of many species may be 

 found in a number of habitats, most 

 species showed distinct preferences. 

 These studies clearly showed the role 

 that hard structure plays for many 

 species. How more subtle habitat char- 

 acteristics, such as the presence of 

 sheltering sites, may influence species 

 composition was still unclear. 



Between 1995 and 2002 we sur- 

 veyed fish assemblages associated 

 with southern California oil and gas 

 platforms. Platforms may serve at 

 least two functions for these fishes. 

 First, the water column around many 

 platforms serves as a nursery ground 

 for a suite of rockfishes {Sebastes spp.) 

 and other fish species, often harboring 

 higher densities of these species than 

 do nearby natural outcrops (Love et 

 al., 2003). Second, platform bottoms, 

 where the platform jacket and well 

 pipes meet the sea floor, may harbor 

 high densities of subadult and adult 

 fishes. Most of these fishes are rock- 

 fishes, but lingcod iOphiodon elon- 



gatus). painted greenling (Oxylebius 

 pictus), and various members of the 

 surfperch family (Embiotocidae) may 

 also be abundant (Love et al., 1999; 

 Love et al., 2003). 



The platforms we surveyed were 

 designed to have large, circular (1 m 

 in diameter) horizontal beams that 

 connect vertical and diagonal jacket 

 elements at or near the sea floor. In 

 some instances, these beams were 

 buried, either by shells that had fall- 

 en from shallow parts of the jacket 

 or by a combination of shells and fine 

 sediment. In other instances, beams 

 were partially exposed (full width of 

 beam or partial width of beam was 

 resting on the sea floor) or completely 

 exposed (thus leaving a gap between 

 the beam and sea floor). During our 

 fish surveys, we noted that fishes 

 appeared to be patchily distributed 

 along the platform bottom and that 

 some species seemed to be respond- 

 ing to the presence or absence of the 

 beam and to the amount of space 

 under the beam. Because the beams 

 are all composed of similarly shaped 

 steel and differ only in the amount 

 of surface exposed, we hypothesized 

 that patterns of fish associations with 

 this structure would present insights 

 into the role that sheltering spaces 

 play in determining species assem- 

 blages in both natural and man-made 

 habitats. 



