Site fidelity and depth utilization of nearshore reef fish on offshore San Pedro shelf petroleum platforms

Abstract

In California, economically important nearshore reef fish inhabit the shallow (<30 m) regions of deep (50-212 m) San Pedro Shelf (SPS) petroleum platforms. To determine the ecological importance of these habitats, the site fidelity and depth/habitat utilization of adult cabezon (Scorpaenichthys marmoratus), California sheephead (Semicossyphus pulcher), grass rockfish (Sebastes rastrelliger), and kelp rockfish (Sebastes atrovirens) was investigated at two platforms. All individuals were detected a mean (SD) of 66.9 ± 36.0% of their total days at liberty (445–578 d), with most individuals still present at platforms at the end of the study. All species displayed significant shifts in diel and seasonal depth utilization, while exhibiting distinct 24 h periodicity in activity patterns. The shallowest horizontal level on platform Edith (15 m) and Eureka (20 m) was the most utilized aspect of habitat by grass rockfish, kelp rockfish, and sheephead, with cabezon primarily utilizing areas deeper than 30 m.