Habitat value of subsea wells and pipelines for fishery target species in Australia

Abstract

Subsea pipelines and wells installed to support the oil and gas industry represent some of the most extensive and numerous anthropogenic structures throughout global marine ecosystems. There remains a paucity of information on the habitat value of these structures for fishery target species and, as a result, little understanding of how decommissioning should be conducted to minimise impacts to populations of these economically and socially important species. We assess the diversity and abundance of species that are targets of recreational and commercial fisheries on 33 subsea wells and 17 pipelines across the tropical northwest and temperate southeast marine regions of Australia. We examine relationships between fish identity and abundance and a range of environmental (e.g., depth, location), infrastructure-specific (e.g., pipeline position, diameter, age, length of pipeline, height of well, position on well), and biological (% cover of epibiota) variables using video filmed by remotely operated vehicles during their routine offshore inspection and maintenance campaigns. A total of 100 fishery target species were observed across subsea well and pipeline infrastructure, 56 species uniquely observed on pipelines and nine unique to wells. The families Lutjanidae (snapper), Serranidae (rock cods, groupers, perch), and Carangidae (trevallies) were most common and abundant on both wells and pipelines. In the northwest, lutjanids were most abundant around the base of wells, in shallow depths, on shorter wells, and where pipelines spanned the seafloor. A greater number of fishery target species and abundance of ocean perch (Helicolenus spp.) were also associated with pipelines that spanned the seafloor in temperate southeast Australia. The combined biomass of three species of snapper on wells in the northwest was 1,270 kg, with production levels for these species on each well estimated to be 105.2 g m2 year-1. The present study serves as an important reference point for informing decommissioning decisions for pipeline and well infrastructure and demonstrates the utility of industry-held data for science. We suggest that key predictor variables identified here be incorporated into comprehensive before-after-control-impact scientific studies for specific fields/assets to enable the prediction of potential impacts of decommissioning scenarios on marine communities present and quantification of such impacts after the decommissioning activity has occurred.

An Assessment of Environmental Impact on Offshore Decommissioning of Oil and Gas Pipelines

“…Table 3. Maximum concentrations of disturbed sediments in the Northwest Hutton sediments (Source: [43]).…”

“…These might escape either during decommissioning or because of mishaps or spills. According to [43], there is a high correlation between concentrations of Cu, Fe, Mg, Mn, Pb, Zn, and total hydrocarbons, as well as the percentage of marine sediments with a diameter of less than 63 mm. The correlation patterns show that these coarser sediments were mixed with finer metal and hydrocarbon-contaminated sediments from drill cuttings, particularly after total and partial removal.…”

The vertical distribution of fish on two offshore oil platforms

“…The ecological value of ROV video, which is often collected haphazardly, remains unclear (Macreadie et al, 2018;McLean et al, 2020). Several studies have opportunistically harnessed ROV footage used in routine oil and gas platform inspections for scientific purposes, both for determining marine growth (Gass and Roberts, 2006;van der Stap et al, 2016;Thomson et al, 2018) and examining fish assemblages on and around offshore platforms (Pradella et al, 2014;Sih et al, 2022) and pipelines Bond et al, 2018;McLean et al, 2022b;Ierodiaconou et al, 2023). Challenges with haphazard data collection and poor video quality were common among studies, however scientific advances were made in each case.…”