548 



Fishery Bullelm 104(4) 



(Rhinogobiops nicholsii), greenstriped, sharpchin, and 

 stripetail rockfishes, painted greenling, pink seaperch, 

 and sanddabs. These species are usually referred to as 

 "soft substrata" or "mixed substrata" fishes. Other taxa 

 were associated more often or almost exclusively with 

 the exposed beam and these are species often categorized 

 in the literature as "reef" species. These included blue, 

 brown, calico, canary, copper, flag, greenblotched, half- 

 banded, pinkrose, squarespot, and vermilion rockfishes, 

 cowcod, bocaccio, pile perch, and sharpnose seaperch. 

 As in natural systems, to a great extent greenspotted 

 rockfishes and non-YOY lingcod inhabited several dif- 

 ferent habitats. 



There is evidence that the crevices, cracks, and caves 

 on both natural and human-made structures, may influ- 

 ence fish species assemblages because they form shel- 

 ters for fishes (Luckhurst and Luckhurst, 1978; Kellison 

 and Sedberry, 1998; Rilov and Benayahu, 1998). In 

 many instances, overall fish abundances are positively 

 correlated with these openings that enhance habitat 

 complexity. On the Pacific Coast, there are only a few 

 observations specifically addressing shelter sites and 

 deeper-water fishes. Caselle et al. (2002), surveying 

 oilfield debris off southern California, examined the 

 influence that structural complexity may exert on fish 

 assemblages. They found that the presence of shelter 

 was one of the most important determinants for high 

 densities of both copper and vermilion rockfishes and 

 played some role in the abundance of a number of other 

 species. Yoklavich et al. (2000) noted that the "rock 

 habitat guild," composed of such species as cowcod, pyg- 

 my (S. wilsoni), and yelloweye rockfishes, were "closely 

 associated with ledges, caves, crevices, and overhangs." 

 Discussing yelloweye rockfish habitat off southeastern 

 Alaska, O'Connell and Carlile (1993) stated that the 

 "occurrence of refuge spaces may be one key to the pres- 

 ence of yelloweye rockfish, which were normally found 

 in areas where refuge spaces were available, even if the 

 surrounding habitat was not their preferred habitat of 

 boulder or broken rock." 



From our research, it was apparent that, among the 

 reef species, there is a "sheltering" guild. These are 

 species (i.e., blue, canary, flag, greenblotched, half- 

 banded, pinkrose, and vermilion rockfishes, cowcod, 

 and bocaccio) for which an exposed beam alone is not 

 sufficient. These taxa tend to be associated with the 

 spaces that provide shelter under that structure. Blue, 

 brown, canary, halfbanded, and vermillion rockfishes 

 and bocaccio were found in particularly large numbers 

 where the gap between beam and sea floor was larg- 

 est (exposures 3 and 4). A few species, such as calico, 

 copper, greenspotted, and pinkrose rockfishes, YOY 

 lingcod, and sharpnose seaperch, although often found 

 along the beams, seemed to avoid the most exposed 

 sections. 



Fishes that either avoided the beam, or at least that 

 part that formed a gap between the beam and the sea 

 floor, tended to be small in size and to fall into several 

 categories. One group, the sanddabs, is adapted to liv- 

 ing on soft substrata. Other species, including blackeye 



goby, greenstriped, rosy, and sharpchin rockfishes, 

 painted greenling, and pink seaperch, are diminu- 

 tive and solitary. Although pink seaperch are found 

 in schools over natural outcrops, we did not see them 

 schooling around platforms. All of these diminutive 

 forms will live in high relief, complex substrata when 

 larger predators have been removed from the system, 

 as occurs on most of the rocky outcrops off southern 

 and central California (M. Love, unpubl. data). How- 

 ever, it is likely they avoid exposed beams because 

 of the presence in the area of high densities of large 

 fishes. 



Variability in habitat complexity, caused by variation 

 in the amount of beam exposure and the size of gap 

 between beam and sea floor, may explain at least one 

 of the between-platform differences we have observed 

 in fish assemblages. In general, platforms occupying 

 similar depths harbor similar fish assemblages (Love 

 et al., 2003). However, an exception was found when 

 comparing fish species at Platform Gail (224 m) and at 

 Platform Harvest (205 m) (Love et al., 2003). In order 

 of density, greenblotched rockfish, bocaccio, greenspot- 

 ted, stripetail, and pinkrose rockfishes dominated the 

 bottom fish assemblage at Platform Gail. Cowcod, al- 

 though not among the top five most abundant fish, were 

 found at higher densities at this platform than at any 

 natural outcrops or other platform that we surveyed in 

 southern California. By contrast, at Platform Harvest, 

 stripetail, greenstriped, greenspotted, greenblotched, 

 and sharpchin rockfishes were most commonly seen. 

 Cowcod were considerably less abundant at this plat- 

 form and we observed almost no bocaccio. Platform 

 Gail contains, on average, the highest mean exposure 

 value (about 2.5 m) and Harvest the lowest (slightly 

 more than 1.0 ml. Most of the common fishes at Gail 

 are representative of complex habitat, those at Harvest 

 of lower relief and softer substrata. 



This research may have a bearing on the ultimate 

 disposition of California platforms. The possibility of en- 

 hancing fish habitats and fish populations at platforms 

 is an important issue in the decommissioning process. 

 In particular, the California Department of Fish and 

 Game has suggested increasing habitat complexity 

 around the bottom of platform jackets by placing quarry 

 rock or other materials around the jacket (Schroeder 

 and Love, 2004). However, to date, augmentation has 

 not been attempted. With the results from our study, 

 we predict that increasing the habitat complexity at 

 platforms will, in some instances, increase the densities 

 of a number of rock or boulder-oriented species, those 

 species that are preferentially found where there is a 

 gap below the bottom beam. 



In addition, the results of this research may also be 

 applied to natural reef studies, particularly those in- 

 volving marine protected areas (MPAs). This research 

 clearly demonstrates that, in terms of habitat prefer- 

 ences of many fish species, not all hard habitat is the 

 same. In fact, this research indicates that it may be 

 possible to predict which species are found around 

 different types of hard structure by the presence 



