Report of the Workshop to evaluate trade-offs between the impact on seafloor habitats and provisions of catch/value (WKTRADE)

The workshop to evaluate trade-offs between the impact of the seafloor habitats and provisions of catch/value (WKTRADE) chaired by Josefine Egevist (Denmark) and Adriaan Rijnsdorp (the Netherlands) met on 28–31 March 2017 at Danhostel, Vejlands Allé 200, 2300, Copenhagen S. The workshop was attended by 20 participants from 9 countries, including representatives from various ICES Working Groups, the fishing industry and experts involved in regional sea’s convention (RSC) work.

This is the last of a series of three workshops (WKBENTH, WKSTAKE, WKTRADE) that ICES has organised to address an advice request from European Commission to “Evaluate indicators for assessing pressure and impact on the seafloor from bottom-contacting fishing. Using this assessment, demonstrate trade-offs in catch/value of landings relative to impacts and recovery potential of the seafloor”. The three workshops and advice process outcomes as a whole were published as ICES Advice and delivered to the EU on 26 June 2017.

In WKTRADE a worked example of an Assessment of the Impact of Mobile Bottom Contacting Gears was carried out using a quantitative mechanistic approach based on population dynamic responses to bottom trawling (PD2). A set of metrics was selected to provide managers with key information for managing impacts of bottom trawling on the seafloor. In addition to the scientific content, it was discussed how the assess-ment outcome could best be presented to a broad audience of stakeholders that are involved in the management.

The proposed “Assessment Information Sheet” provides illustrations of the pressure, seafloor status, impact and on the trade-off between impact and landings or value sup-plemented with short text. Candidate Figures and Tables are presented to populate the Assessment Information Sheet. Pressure from bottom-contacting fishing gears in the assessment year, estimated as the swept area ratio per c-square (SAR), is presented in a map together with a map of the seafloor habitats. The sheet further presents the tem-poral development of the areal extent (footprint) in region and habitats, the degree of aggregation of the trawling activities within the footprint, the temporal development in the average status of the seafloor in the region and main seafloor habitats, the tem-poral development of the impact in region and habitats of a selection of metiers. Finally information is presented about the relation between the status and the value or land-ings per unit of impact. It is important to note that the impact assessment presents a static picture of these relationships.

The assessment shows that bottom trawling is aggregated in a relatively small part of the footprint. The status of the seafloor at these core fishing grounds was poor but the catch rate per unit of impact was higher than in the peripheral fishing areas. These peripheral areas had a higher status, while they had a relatively small contribution to the overall landings and value. The relative high catch per unit of impact in the core fishing grounds implies that a reduction of fishing impact might be achieved with a lower cost in landing reduction by limiting fishing pressure in the peripheral grounds as compared to a reduction of fishing in the core fishing grounds. The ecological ra-tionale for eliminating or reducing the pressure at low trawling intensities is also that the most sensitive species are affected already at low trawling intensities. In contrary, a marginal increase in the pressure at high trawling intensities will have little effect as the assemblage in these areas are primarily comprised of species resilient to trawling.

The testing of management scenarios in WKTRADE report also show that spatial man-agement measures that focus on protecting the peripheral fishing grounds (instead of the core fishing ground) and replacing effort to the core fishing ground will improve the average status of the seafloor. Whether it will contribute to an increase in the pro-portion of the seafloor above the threshold depends on the threshold level set and to the proportion of the effort reallocated. Reallocating effort from the core fishing ground will reduce the average status of the seafloor.

When evaluating management options to improve the status of the seafloor, trade-offs between impact and landings or value can best be evaluated on the level of the metier The implications of spatial management measures cannot be based on the static infor-mation provided in the standard assessment sheets only. Fisheries are by nature dy-namic and response to changes in their environment. Models on the dynamics of the fisheries are required to assess the potential implication of the displacement on the level of the fisheries and individual companies.

The interconnectivity of all marine life through the food web means that every man-agement action will have an effect to some degree on every part of the system. So measures designed to mitigate impacts on seabed integrity can be expected to have indirect effects elsewhere in the food web, even on top-predators. Preliminary results from food web modelling suggest that these may amount to a few percent changes at the regional scale. A consequence of these effects is that metiers such as static gears which are considered non-damaging and not subject to spatial management, will ex-perience indirect, collateral effects on their catch rates as a result of managing seabed contact gears.