Bottom trawl-fishing footprints on the world’s continental shelves

Bottom trawlers land around 19 million tonnes of fish and invertebrates annually, almost one quarter of wild marine landings. The extent of bottom trawling footprint (seabed area trawled at least once in a specified region and time period) is often contested but poorly described. We quantify footprints using high resolution satellite Vessel Monitoring System (VMS) and logbook data on 24 continental shelves and slopes to 1000m depth, over at least two years. Trawling footprint varied markedly among regions, from <10% of seabed area in Australian and New Zealand waters, the Aleutian Islands, East Bering Sea, South Chile and Gulf of Alaska to >50% in some European seas. Overall, 14% of the 7.8 million km2 study area was trawled and 86% not trawled. Trawling activity was aggregated; the most intensively trawled areas accounting for 90% of activity comprised 77% of footprint on average. Regional swept-area ratio (SAR) (ratio of total swept-area trawled annually to total area of region, a metric of trawling intensity) and footprint area were related, providing a new approach to estimate regional trawling footprints when high resolution spatial data are unavailable. If SAR was ≤0.1, as in 8 of 24 regions, there was >95% probability that >90% of seabed was not trawled. If SAR was 7.9, equal to the highest SAR recorded, there was >95% probability that >70% of seabed was trawled. Footprints were smaller, and SAR ≤0.25, in regions where fishing rates consistently met international sustainability benchmarks for fish stocks, implying collateral environmental benefits from sustainable fishing.