Quantifying fishing activity targeting subsea pipelines by commercial trap fishers

Over 1400 km of oil and gas pipeline infrastructure exists within the boundaries of the Pilbara Trap Managed Fishery (PTMF) operating on the North West Shelf of Australia. Some of this infrastructure has reached the end of its operational life and requires decommissioning. Location and speed data collected from 2008 to 2018 using vessel monitoring systems onboard all trap fishing vessels (n = 3) operating in the PTMF were used to understand how fishing activity near pipelines has changed through time, and to identify the best predictive variables to explain hours spent fishing km⁻² week⁻¹. The proportion of fishing activity within 200 m of a pipeline increased over the survey decade and averaged 4.2% across all years. Hours spent fishing km⁻² within 200 m of any pipeline was found to be 8.0 h km⁻², ~ 11.4 times more than that recorded, on average, for the remaining area of the PTMF (0.7 h km⁻²), and ~ 4.6 times more than the western portion of the PTMP (1.7 h km⁻²) where all pipeline infrastructure exists. Fishing activity within 1 km of pipelines increased after their installation, and hence time since installation was the best predictor of fishing. This study demonstrated that trap fishers in the PTMF allocate a small proportion of their time targeting pipeline infrastructure, with the area close to a pipeline experiencing a relatively greater magnitude of fishing than that elsewhere in the PTMF. As such, the results of this study provide decision makers with an understanding of the intrinsic value of this infrastructure to trap fishers.