Regional Variation in Active Bottom-Contacting Gear Footprints

Fishing with active bottom-contacting gears (here collectively described as 'bottom trawling') is considered the greatest source of anthropogenic disturbance to marine sediments. However, uncertainties are apparent in studies evaluating the severity of their impacts from fishing with these gears at the global scale. A major uncertainty is the estimation of the area of seabed disturbed by applying European-based vessel size to gear footprint (i.e., gear width) relationships to the global fleet, thereby assuming these relations hold worldwide. To test the strength of this assumption, we conducted a structured review to understand global variation in fishing gear parameters and, thus, footprint of bottom trawling gears. While we find a European bias in the primary literature, we find that the relationship between vessel size and gear footprint differs significantly among FAO Major Fishing Areas, suggesting that European-based relationships are not representative of fleets worldwide. For example, otter trawler footprints in the Mediterranean and the Black Sea increase by 10.2 m for every meter increase in overall vessel length compared to just 3.3 m for otter trawlers in the Northwest Atlantic. These findings challenge the reliability of previous estimates of the global footprint of bottom trawling gears, thus highlighting the urgent need for improved availability of commercial data to create a globally representative data set that can address uncertainties in the quantification of anthropogenic disturbance of the benthic environment and the consequential impacts on biodiversity, ecosystem integrity and carbon losses.