Effects of an offshore oil platform on the distribution and abundance of commercially important crab species

Abstract

The distribution, abundance, and population charactenstics of large, highly mobile crab species (Cancer antennan.us, C. anthonyi, C. productus, Loxorhynchus grandis) differed in relation to an offshore oil platform in the Santa Barbara Channel, California, USA. Only C. antennanus individuals recruited onto the platform. primarily into the attached community of Mytilus gaUoprovincialis and M. californianus at depths of <12 to 15 m. The higher CPUE (catch per unit effort) of C. antennarius beneath the platform, compared with nearby soft bottom stations, suggested that this species remained pnmarily in the vicinity of the platform. Although C. anthonyi did not recruit at the platform, adult female C. anthonyi were attracted to the platform from surrounding habitat. The higher CPUE of female C. anthonyi beneath the platform, compared with soft bottom stations, suggested that habitat selection is related to reproduction in this species. C. productus and Loxorhynchus grandis were present in low nurnbers at aii benthic stations. The distnbution and abundance of these crab species fit into 3 of 4 hypothesized scenanos that descnbed different combinations of recruitment, distnbution and abundance of mobile species around oii platforms: (1) 'recruitmenWemigration', a platform provides recruitment habitat and individuals that recruit to the platform ernigrate at some point to the surrounding environment, (2) 'recruitmenWresident', a platform provides recruitment habitat, but individuals remain in the vicinity of the structure (C. antennanus), (3) 'attraction', individuals that recruited elsewhere are attracted to and aggregate at a platform (C. anthonyi), and (4) 'visitor', individuals that recruited elsewhere occur temporarily at the plafform without aggregation (C. productus, L. grandis). Our results. in the context of these scenanos. dustrate the need to consider the responses of individual species to artificial structures.