The physical seafloor impact of mobile, bottom contacting fishing gear is a hot topic in discussions between environmental organizations and the fishing industry, and also receives a lot of attention from the public. In EU marine environmental policy, fishing pressures are a central component in Ecosystem Based Management. Ecolabels for seafood (e.g. MSC) also increasingly use the fishing pressure as part of their criteria.
Fishing pressure indicators, such as swept area and impact severity, are usually calculated on the basis of satellite based Vessel Monitoring Systems (VMS) coupled with logbook data. Unfortunately the existing logbook statistics account very poorly for the differences in size and design of the fishing gears deployed. For example, beam trawlers fishing for flatfish use chain mats and tickler chains, while shrimp beam trawlers use much lighter gears.
The article by Eigaard et al. (2015) presents a new generic method, developed within the EU 'BENTHIS' project, which substantially improves the ability to estimate the fishing pressure on the seafloor from logbook and VMS information.
Based on information obtained from the industry, the authors defined 14 distinct towed gear groups (eight otter trawl groups, three beam trawl, two demersal seine, and one dredge). The physical impact on the seafloor per individual gear component (such as doors, sweeps, beam shoes, ground gear) was then estimated. This resulted in a total footprint per gear, with each footprint being defined as the relative contributions made by these individual parts to the total area and severity of the gear's impact.
Next the authors generated impact comparisons for average-size vessels of each fishing gear group, based on relationships between ship size and gear size used. The Scottish seine fisheries for cod, haddock and flatfish showed the largest surface area swept per hour (1.6 km2/hour), but had less impact underneath the seafloor surface (0.1 km2/hour), compared to for example Nephrops (Norway lobster) otter trawl fisheries (1.2 and 0.3 km2/hour, respectively).
The insights and results obtained will have substantial implications for the definition, estimation and monitoring of fishing pressure indicators in the context of an ecosystem approach to fisheries management.
Traditional beam trawl for flatfish in the North Sea. The gear footprint was established by combining impact estimates for the individual gear components such as the shoes and the tickler chains. Photo: F. Quirijns/IMARES