Niels T. Hintzen

The footprint of bottom trawling in European waters: distribution, intensity, and seabed integrity

Mapping trawling pressure on the benthic habitats is needed as background to support an ecosystem approach to fisheries management (EAFM). The extent and intensity of bottom trawling on the European continental shelf (0–1000 m) was analyzed from logbook statistics and VMS data for 2010, 2011 and 2012 at a resolution of 1×1 minutes longitude and latitude. Trawling intensity profiles with seabed impact at the surface and subsurface level are presented for 14 management areas in the North-east Atlantic, Baltic Sea and Mediterranean Sea. The footprint (proportion of the seabed trawled 1 or more times every ten years) ranged between 40–90% across EUNIS habitats with largest footprints observed in sandy (A5.2) and muddy (A5.3) habitats. The footprint of the management areas ranged between 52-99% and 5-94% for the depth zone from 0–200 m (Shallow) and from 201–1000 m (Deep), respectively. The footprint was estimated as the total area of all grid cells that were trawled fully or partially. Excluding these untrawled proportions reduced the footprint estimates to 28-85% and 2-77%. Mean trawling intensity ranged between 0.5 and almost 8.5 times per year, but was less in the Deep zone with a maximum intensity of 6.4 times per year. Highest intensities were recorded in the Skagerrak–Kattegat and Adriatic Sea. Largest footprints per unit landings were observed in the Mediterranean Sea. Bottom trawling was highly aggregated. The seabed area where 90% of the effort occurred comprised between 11% and 65% (median 44%) of the total area trawled. Using the longevity distribution of the untrawled infaunal community, the seabed integrity was estimated as the proportion of the biomass of benthic taxa where the trawling interval at the subsurface level exceeds their life span. Seabed integrity was low (<0.1) in large parts of the European continental shelfs, although smaller pockets of seabed with higher integrity values occur. The methods developed here integrate official fishing effort statistics and industry-based gear information to provide high-resolution pressure maps and indicators, which greatly improve the basis for assessing and managing benthic pressure from bottom trawling. Further they provide quantitative estimates of trawling impact on a continuous scale by which managers can steer.

Evaluating Biological Robustness of Innovative Management Alternatives

The influence of innovative management alternatives (participatory governance, effort management, decision rules) on biological robustness (BR) in various fisheries relevant to the EU (Baltic, Western Shelf, Faroe Islands, North Sea), was investigated with a numerical simulation model developed in the EU projects EFIMAS (2004–2008) and COMMIT (2004–2007). The index for BR was set as the percentage of years in which standard biological reference points (Bpa, Fpa) were met. The results suggest that new information obtained through participatory governance may affect BR by reducing bias rather than increasing precision, implying that participatory governance should rather focus on potential sources of bias than on (perceived) low sampling efforts. Further analyses suggest that effort-based regimes combined with catch quota restrictions improve BR. However, the relative effect of catch quotas versus effort management on BR varies with circumstances, implying that careful and case-specific analyses are needed to weigh one against the other. This requires more detailed data than generally available at present, including electronic surveillance, detailed catch data, environmental/productivity data, recruitment and misreporting. Finally we analysed a decision rule consisting of a two-step management system, which allows TAC adjustment according to the state of the stock monitored during the fisheries season. Such measures may improve the BR.

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

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.

Shifts in North Sea forage fish productivity and potential fisheries yield

1. Forage fish populations support large scale fisheries and are key components of marine ecosystems across the world, linking secondary production to higher trophic levels. While climate-induced changes in the North Sea zooplankton community are described and documented in literature, the associated bottom-up effects and consequences for fisheries remain largely unidentified. 2. We investigated the temporal development in forage fish productivity and the associated influence on fisheries yield of herring, sprat, Norway pout and sandeel in the North Sea. Using principal component analysis, we analysed 40 years of recruitment success and growth proxies to reveal changes in productivity and patterns of synchroneity across stocks (i.e. functional complementarity). The relationship between forage fish production and Calanus finmarchicus (an indicator of climate change) was also analysed. We used a population model to demonstrate how observed shifts in productivity affected total forage fish biomass and fisheries yield. 3. The productivity of North Sea forage fish changed around 1993 from a higher average productivity to lower average productivity. During the higher productivity period, stocks displayed a covariance structure indicative of functional complementarity. Calanus finmarchicus was positively correlated to forage fish recruitment, however, for growth, the direction of the response differed between species and time periods. Maximum sustainable yield (MSY) and the associated fishing mortality (Fmsy) decreased by 33%–68% and 26%–64%, respectively, between the higher and lower productivity periods. 4. Synthesis and applications. The results demonstrate that fisheries reference points for short-lived planktivorous species are highly dynamic and respond rapidly to changes in system productivity. Furthermore, from an ecosystem-based fisheries management perspective, a link between functional complementarity and productivity, indicates that ecosystem resilience may decline with productivity. Based on this, we advise that system productivity, perhaps monitored as forage fish growth, becomes an integral part of management reference points; in both single species and ecosystem contexts. However, to retain social license of biological advice when fish catch opportunities are reduced, it is crucial that shifts in productivity are thoroughly documented and made apparent to managers and stakeholders.

Estimating sensitivity of seabed habitats to disturbance by bottom trawling based on the longevity of benthic fauna

Abstract Bottom fishing such as trawling and dredging may pose serious risks to the seabed and benthic habitats, calling for a quantitative assessment method to evaluate the impact and guide management to develop mitigation measures. We provide a method to estimate the sensitivity of benthic habitats based on the longevity composition of the invertebrate community. We hypothesize that long‐lived species are more sensitive to trawling mortality due to their lower pace of life (i.e., slower growth, late maturation). We analyze data from box‐core and grab samples taken from 401 stations in the English Channel and southern North Sea to estimate the habitat‐specific longevity composition of the benthic invertebrate community and of specific functional groups (i.e., suspension feeders and bioturbators), and examine how bottom trawling affects the longevity biomass composition. The longevity biomass composition differed between habitats governed by differences in sediment composition (gravel and mud content) and tidal bed‐shear stress. The biomass proportion of long‐lived species increased with gravel content and decreased with mud content and shear stress. Bioturbators had a higher median longevity than suspension feeders. Trawling, in particular by gears that penetrate the seabed >2 cm, shifted the community toward shorter‐lived species. Changes from bottom trawling were highest in habitats with many long‐lived species (hence increasing with gravel content, decreasing with mud content). Benthic communities in high shear stress habitats were less affected by bottom trawling. Using these relationships, we predicted the sensitivity of the benthic community from bottom trawling impact at large spatial scale (the North Sea). We derived different benthic sensitivity metrics that provide a basis to estimate indicators of trawling impact on a continuous scale for the total community and specific functional groups. In combination with high resolution data of trawling pressure, our approach can be used to monitor and assess trawling impact and seabed status at the scale of the region or broadscale habitat and to compare the environmental impact of bottom‐contacting fishing gears across fisheries.