Impact of fisheries on seabed bottom habitat: fisheries from The Netherlands, Germany, Denmark and Sweden

Gerjan Piet, Niels Hintzen, Floor Quirijns

Research output: Book/ReportReportProfessional


The Marine Stewardship Council (MSC) released new certification requirements in 2014. The new requirements come with new guidelines for scoring fisheries for several Performance Indicators (PIs). One of the adjusted PIs is PI 2.4.1: the Habitats outcome indicator:“The Unit of Assessment (UoA) does not cause serious or irreversible harm to habitat structure and function, considered on the basis of the area(s) covered by the governance body(s) responsible for fisheries management.”Up to now, the new guidelines for this PI have not yet been translated into an operational performance indicator. An international group of fisheries organisations, from the Netherlands, Denmark, Germany and Sweden, is interested in applying for MSC accreditation or for renewal of existing accreditation. For them it is relevant to know how the new guidelines for PI 2.4.1 translate into a scoring of their fisheries. Therefore, the fisheries organisations requested WMR to develop a methodology for assessing fisheries’ impact on the North Sea seabed which could be used in assessments for MSC accreditation.WMR combined the MSC guidelines with a methodology for assessing fisheries’ impact on the seabed developed in collaboration with partners in the International Council for Exploration of the Sea (ICES). A so-called ‘Population Dynamic’ method was applied, which indicates how bottom trawling affects the biomass of the benthic community relative to an undisturbed situation. Recovery of a habitat is an important aspect in determining whether serious or irreversible harm is caused by a fishery. The benthic invertebrate community consists of many different taxa that differ in their sensitivity to fishing disturbance. This difference in sensitivity is reflected in the parameterisation which distinguishes between an average sensitivity (sensitivity I) and a high sensitivity (sensitivity II). Recovery of Seabed Integrity (SI) is used as an indicator for serious or irreversible harm. This methodology was applied for habitats with status type ‘commonly encountered’. Data that were used are satellite (VMS) and logbook data giving information on the spatial distribution and intensity of the fisheries. Information on North Sea habitats was obtained from EMODnet EU Sea Map and data on recovery rates and gear specific impact rates were obtained from an EU project called ‘BENTHIS’. The methods were applied to 11 UoAs for four different countries, in four different management areas (North Sea, Skagerrak, Kattegat and Eastern English Channel).The analysis comprised of a definition of the current state of seabed integrity (SI), based on historic fishing intensity. For each UoA a study area or ‘footprint’ was defined by gear and management area. Next, for each grid cell (1-minute longitude by 1-minute latitude) the fishing intensity was calculated from VMS data for three different gear groups: Beam Trawl (BT), Demersal Otter Trawls (TR) and Danish Seine (SDN). It was then possible to assess recovery rates for each grid cell (relative increase of biomass per year). The SI was calculated for the moment right after fishing impact and then for respectively 1, 5, 10 and 20 years after ceased fishing. Two indicators were used to assess whether recovery of the habitat to 80% of its unimpacted structure was achieved:- T80% > 0.95K: the top 80% of least impacted grid cells have an SI of at least 0.95 K, meaning that biomass is at more than 95% of the carrying capacity (K).- 100% > 0.80K: all grid cells in the study area have an SI of at least 0.80 K, so biomass is more than 80% of K.For habitats with status type ‘Vulnerable Marine Ecosystem’ (VME) we did not apply the methodology. In order not to cause any serious or irreversible harm to VMEs, the VMEs should not be fished at all. If that is taken into account during assessments for MSC accreditation, it is not relevant whether the VME habitat recovers. We did overlay maps of fishing by UoA with maps of vulnerable habitats (based on either ICES or OSPAR data) in order to see whether VMEs may be a relevant theme during assessments for MSC accreditation.Habitats with status type ‘minor’ were not considered, as with our interpretation these are insignificant in the North Sea and data for carrying out the above (or any) methodology is lacking.The analyses show that for the scenario with Sensitivity I (average recovery rates) none of the UoAs causes serious or irreversible harm to the commonly encountered habitats. I.e. recovery up to 80% is achieved within 20 years for both indicators. If the other Sensitivity is applied (II, with lowest recovery rates), the results are different. The ‘T80% > 0.95K’ indicator always reaches the threshold value within 20 years, but the ‘100% > 0.80K’ indicator does not reach the threshold value for 6 UoA. The 6 UoAs are the TR groups from Denmark (North Sea and Skagerrak), Germany (North Sea), the Netherlands (North Sea) and Sweden (Skagerrak) and the BT group from the Netherlands (North Sea). This may mean – dependant on whether both indicators should reach the threshold value or not – that for these 6 UoA it could be concluded that they do cause serious or irreversible harm to the habitat.Overlaying fishing activities by UoA with VMEs in the North Sea show us that there may be an issue for the German TR unit on the North Sea. This UoA has a minimal overlap with VMEs according to the ICES database. However, if data on threatened and/or declining species and habitats from OSPAR are used, a larger overlap is found. The methodology developed in this study can be a useful starting point for assessing the impact of fishing on the sea bed. It is not yet fully developed to be used in the framework of MSC accreditation: there are still several issues to be dealt with. First of all, a decision needs to be made on which performance indicator(s) to use: the ‘T80% > 0.95K’ indicator or the ‘100% > 0.80K’ indicator, or both. Second, a choice needs to be made about the sensitivity to be used.Another issue that needs to be considered concerns the UoAs. Each UoA may have a negligible impact on the seabed compared to the whole fleet. However, all UoAs together may cause serious or irreversible harm to the seabed. It is therefore important to be aware of the context in which the UoA is practicing the fishery.
Original languageEnglish
Place of PublicationIJmuiden
PublisherWageningen Marine Research
Number of pages51
Publication statusPublished - 5 Mar 2018

Publication series

NameWageningen Marine Research rapport


Dive into the research topics of 'Impact of fisheries on seabed bottom habitat: fisheries from The Netherlands, Germany, Denmark and Sweden'. Together they form a unique fingerprint.

Cite this