Determining the Ecological Value of Fish Resources at Platform Decommissioning Sites using ROV and Trapping Techniques in the Santa Barbara Channel, California, USA

Abstract

Abstract As part of decommissioning four platforms off the coast of California (USA), the underlying drill cutting mounds were left behind. These mounds are covered with several meters of "shell hash" from bivalve shells dislodged from the platform jacket and natural sedimentation that has accumulated in the 30+ years following cessation of drilling activities. Previous studies have indicated that the "shell mounds" provide a complex hard bottom habitat and support a variety of fish and invertebrate species typical of a natural hard bottom community. This paper describes field studies to further characterize the ecological utilization by fish and invertebrates of the shell mounds and the surrounding soft bottom areas of Santa Barbara Channel. Initially, ROV surveys were performed to provide video transects of fish use. However, poor visibility limited the usefulness of the ROV approach. A multi-season fish trapping study using standard commercial fish traps is currently being conducted and the results of the first two deployments are presented and discussed. The assemblage of fish and invertebrates observed in the fish traps from the mounds include several species of rockfishes (genus Sebastes), ling cod, rock crabs, whelks and bat stars that are typical of natural hard bottom communities in the Santa Barbara Channel. Results to date indicate that the shell mounds have more fish and invertebrates and a more diverse benthic community than the soft-bottom reference areas. This preliminary investigation supports previous studies that indicated that fish habitat value of the shell mounds is greater than that of the surrounding soft bottom habitat and supports leaving the mounds in place.