The value of Subsea pipelines to marine biodiversity

Abstract As offshore oil and gas infrastructure reaches the end of its operational life, owners and regulators will question the best options available to decommission it, with decisions requiring information about the potential ecological value of these structures and the environmental impact of their removal. Using a combination of existing industrial underwater Remotely Operated Vehicle video data and marine scientific remote stereo-video surveys, we describe and compare the fish assemblage on pipelines with those on the adjacent natural seafloor of the North West Shelf of Western Australia. Using these video observations of commercially important fish species on pipelines we were able to summarise the potential monetary value of commercial fish found on pipelines to commercial fisheries. Greater numbers of fish were observed on pipelines, compared with that seen on adjacent seafloor areas, and the monetary value of the fish found on the pipelines was estimated to be ca. six times greater than that of fish in surrounding areas lacking subsea infrastructure. Pipeline spans had high fish abundance, with fish appearing to utilise these spans as refuges. These results, together with allied assessments of marine growth on pipelines, suggest over the course of their operating lives, pipelines gain ecological and fishery value, enhancing the diversity and abundance of fish (including important commercial species) which can be translated to a monetary value for commercial fisheries. With an extensive array of pipeline infrastructure spread across the North West Shelf of Western Australia, knowledge of the ecological and fisheries value of subsea infrastructure is imperative to understanding the environmental and economical consequences of removing infrastructure as part of decommissioning. Where pipelines add value to marine biodiversity and fisheries in Western Australia, engineers and ecologists can work towards quantifying this value and preserving it – and potentially also enhancing it – via novel evidence-based abandonment strategies.