An analysis of the fish assemblages around 23 oil and gas platforms off California with comparisons with natural habitats

Between 1995 and 2013, we surveyed fishes living around 23 California offshore oil and gas platforms (midwaters, bases, and shell mounds) and 70 natural habitats. These platforms were distributed between about Point Arguello, central California, and Huntington Beach, southern California, had seafloor depths between 49 and 363 m, and were surveyed between one and 16 times. A total of 1,526,437 fishes were observed. Fish densities were highest around platform bases, followed by platform midwaters, shell mounds, and natural habitats. Of all fishes observed, 90.4% were in the genus Sebastes. Water depth was the strongest driver of the fish species assemblages, although habitat type and geographic location were also important. Most of the fishes living around platforms and natural habitats were relatively small, primarily ≤20 cm in length. Many of these individuals were the juveniles of larger taxa or the juveniles and adults of dwarf species. Larger fishes were less common and these were most often found around platform bases and on natural habitats. Most young-of-the-year (YOY) fishes occurred at water depths of ≤150 m at all four habitats. At platforms, YOY densities were highest in platform midwaters and bases. On average, densities of these young fishes were somewhat higher compared to natural habitats and it is likely that many, although not all, California platforms play a significant role as nursery grounds for a variety of fishes, particularly for a number of Sebastes species.