A comparison of the fish assemblages associated with an oil/gas pipeline and adjacent seafloor in the Santa Barbara Channel, southern California bight

An oil pipeline and its surrounding seafloor, located in the Santa Barbara Channel, southern California, were surveyed for fishes using a manned research submersible. The parts of the pipeline and seafloor surveyed were situated in waters 95-235 m deep. Some sections of the surveyed pipe were covered with both sessile and motile invertebrates, such as sea anemones (Metridium cf. farcimen) and sea urchins (Allocentrotus fragilis), sea stars (particularly Hippasteria cf. spinosa and Stylasterias cf. forreri), basket stars (Gorgonocephalus eucnemis), spot prawns (Pandalus platyceros), and king crabs (Paralithodes californiensis). Based on differences in fish assemblages, four habitats (shallow and deep pipeline and shallow and deep seafloor) were categorized. Fish densities along the shallow portion of the pipeline were about seven times higher than on the adjacent seafloor and densities along the deep pipeline portion were nearly six times that of the deeper seafloor. Along the pipeline, rockfishes comprised 84% of the fishes and included 22 species. Unidentified sanddabs (probably most or all Citharichthys sordidus), forming 33.2%, and combfishes (Zaniolepis frenata and Z. latipinnis), comprising 19% of the total, were most often observed on the seafloor. Most of the fishes living on the pipeline were either juveniles of such larger taxa as blackgill (Sebastes melanostomus), flag (S. rubrivinctus), and vermilion (S. miniatus) rockfishes, cowcod (S. levis), and lingcod (Ophiodon elongatus), or diminutive species such as halfbanded (S. semicinctus) and stripetail (S. saxicola) rockfishes, combfishes (Zaniolepis spp.), and poachers (Family Agonidae). Higher densities of fishes were often noted in areas of the pipeline that had been undercut. Of particular interest were the relatively high densities of juvenile cowcod along the deeper parts of the pipeline, densities that were far higher than any seen at over 80 natural outcrops and at ten platforms. We suggest that, in the process leading to oil platform and pipeline decommissioning, it is important to understand the role that human-made structure plays as fish habitat.