Recruitment of young-of-the-year fishes to natural and artificial offshore structure within central and southern California waters, 2008–2010

Abstract

Many of the oil and gas platforms off California harbor high densities of young-ofthe- year (YOY) fishes, primarily rockfishes (genus Sebastes). One decommissioning option for these platforms is “topping,” cutting the structure some distance below the water line and leaving the rest of the jacket in place. Questions have arisen regarding how this option would affect the nursery function of the remaining structure. Between 2008 and 2010, we surveyed the densities of YOY fishes at seven intact platforms, as well as six reefs and three shipwrecks that did not crest near the surface and thus might act as surrogates for topped platforms. Rockfishes of about five species dominated the deeper parts of the platforms, reefs, and shipwrecks, while YOY blacksmith, Chromis punctipinnis (Cooper, 1863), were most characteristic of the shallow portions of platforms. Over the course of the study, we observed large fluctuations in the recruitment success of fishes; recruitment of rockfishes was particularly successful in 2010, while particularly poor for blacksmith in the same year. This interannual pattern was observed throughout our study sites. In general, the YOY fish assemblages around the deeper parts of the platforms were similar to those around the reefs and shipwrecks, implying that removing the shallow parts of California platform may have relatively little effect on juvenile rockfish recruitment; however, blacksmith recruitment to platforms will likely decrease. Although offshore oil and gas structures have been present in US waters since