Fishes with high reproductive output potential on California offshore oil and gas platforms

Reproductive output can serve as an important metric to assess the value of a marine habitat as it combines fish densities, size at maturity, and the exponential increase of fecundity with body length. California may permit some portion of the structures of offshore oil and gas platforms to remain in place if a "net benefit to the marine environment" can be demonstrated. Here we assess habitats at 23 oil and gas platforms in terms of site- and species- specific estimates of potential reproductive output. We identified 17 fish species (15 rockfishes Sebastes spp.) that have potential reproductive output densities (no. eggs m^–2) on individual platforms that were tens to hundreds of times their average on natural reefs in the study area, with the highest potential reproductive output values being observed on platforms for all but two of these species. These extreme values were typically observed in platform base habitats, and likely result from the combined effects of high levels of fish recruitment to midwater platform habitats, relatively low fishing activity on these structures, and ontogenetic habitat use (depth-specific) patterns that make some platforms better habitats for some species based on the seafloor depth where they are sited. However, spatial variability was also very high across both platform and natural reef sites, including reproductive potential for almost all focal species being zero at the majority of surveyed sites. The contribution of fish reproductive potential to the discussion of decommissioning alternatives should therefore be considered on a case-by-case basis for each platform in California.