Site fidelity, vertical movement, and habitat use of nearshore reef fishes on offshore petroleum platforms in southern California

Abstract

Off California, economically important nearshore reef fishes inhabit the shallow (<20 m) regions of offshore petroleum platforms on the San Pedro Shelf (SPS). It is essential to understand the degrees to which platforms support fish over time to indicate whether biological requirements (e.g., shelter, diet, reproduction) are being met. To determine the ecological importance of platforms as fish habitat, the site fidelity and depth/habitat use of adult cabezon, Scorpaenichthys marmoratus (Ayres, 1854), grass rockfish, Sebastes rastrelliger (Jordan and Gilbert, 1880), kelp rockfish, Sebastes atrovirens (Jordan and Gilbert, 1880), and California sheephead, Semicossyphus pulcher (Ayres, 1854) were investigated at platforms Edith (50 m bottom depth) and Eureka (212 m). A total of 63 fish were acoustically tagged and monitored for up to 578 d. Sixty-three percent of individuals were still present at platforms at the end of the study (long-term site fidelity), with 55 individuals detected a mean of 66.9% (SD 36.0%) of their total days at liberty (daily site fidelity). All species displayed a shift in seasonal depth use. The shallowest horizontal level, consisting of various horizontal beams at platform Edith (15 m depth) and Eureka (17 m), was the most utilized habitat by grass rockfish, kelp rockfish, and California sheephead. Cabezon at platform Eureka utilized depths (21-31 m) unassociated with horizontal levels, while at platform Edith they primarily utilized the second horizontal level (30 m). Decommissioning options that remove the shallowest 26 m of structure would eliminate the habitat most utilized by three of the four study species that dominate the nearshore reef fish communities at SPS platforms.