Dab in the Greater North Sea, Demersal otter trawl

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1 Dab in the Greater North Sea, Demersal otter trawl Content last updated 6th Mar 2018 Stock: Dab in ICES subarea IV and division IIIa, Greater North Sea Management: EU Dab in the Greater North Sea, Demersal otter trawl Overview Dab (Limanda limanda) is a widespread demersal species on the Northeast Atlantic shelf and distributed from the Bay of Biscay to Iceland and Norway, including the Barents Sea and the Baltic. In the North Sea it is one of the most abundant species distributed over the whole area in depths down to 100m, but it was also found occasionally down to depths of 150m. The main concentration of dab can be found in the south eastern North Sea. Dab feeds on a variety of small invertebrates, mainly polychaete worms, shellfish and crustaceans. Early sexual maturation was reported for dab, maturing at ages of 2 to 3 years corresponding to approximately 11 to 14cm. Peak spawning in the south eastern North Sea occurs from February to April. Because of its sedentary nature, dab has proved to be a valuable indicator in eco-toxicological studies. Dab is among the most discarded fish species in the North Sea and catches are mainly from beam trawl fishery on sole and the otter trawl fishery on plaice. The largest part of the landings in the North Sea are taken by the Netherlands, and in Skagerrak and Kattegat, Denmark lands the highest quantity. The ICES advice for dab in the North Sea is based on the data limited approach and the stock appears to have remained stable over the last 20 years. Stock Status less risk more risk Dab in Sub area IV and division IIIa has been scored moderate risk. This is because the species has a low to moderate vulnerability score of 40/100 and the most recent stock assessment is indicative of trends only. The biomass (SSB) has been increasing since Total mortality (Z) has declined since Recruitment (R) showed an increasing trend until 2014, but has declined in the latest two years of the time-series. Management less risk more risk The management of dab in Sub area IV and division IIIa has been scored a low risk. This is because management decisions are informed by an analytical (although data limited) stock assessment, and there is a complex regulatory framework in place. ICES advised that the risk of having no catch limits for the stocks of dab and flounder is currently considered to be low and not inconsistent with the objectives of the Common Fisheries Policy. Bycatch less risk more risk The bycatch risk in this fishery has been scored a high risk. This is because otter trawls have the potential to take relatively high quantities of bycatch (> 40% of catch weight). However, the cod recovery plan has been implemented in this area and this is expected to have had an influence on the discarding levels in North Sea demersal fisheries and the incoming EU landings obligation is also intended to reduce discarding. There are also catches of demersal elasmobranchs and protected, endangered and threatened (e.g. sharks and rays) species in certain circumstances. Habitat less risk more risk The habitat risk of this fishery has been scored a high-moderate risk. This is because, although otter trawls are considered to have a potential to cause significant habitat damage, damage to vulnerable and sensitive marine habitats is likely to be minimised given that the footprint of the fishery is within core areas, typically historically fished ground. Spatial management to reduce potential interactions with vulnerable habitats are being developed, as there remains uncertainties about the location of some sensitive seabed habitats so these remain at risk. Outlook Current risk status Outlook Reason

2 Stock Moderate Stable The assessment indicates that there has been a stable stock biomass over the last 20 years and it is likely to remain stable in the future. Management Moderate Stable The CFP is going through reform and thus there is some uncertainty on how this will impact fisheries management in the North Sea. There is concern over the use of a combined TAC for the two species, dab and flounder, which carries the risk of one of the species being overexploited. Bycatch High Improving Bycatch of non-target species in this fishery is relatively high with poor selectivity. However, with technical and spatial management measures continuously under development and the incoming EU landings obligation intended to reduce discarding of managed species, the bycatch risk is likely to reduce in the future. Habitat Moderate Improving Otter trawls have the potential to affect seabed habitats, but spatial management measures are continuously being developed and will likely reduce the risk. As planned networks of Marine Protected Areas become established, larger areas of sensitive habitat will become protected from trawling. Type Current Risk Status Outlook Reason Stock Moderate Stable The assessment indicates that there has been a stable stock biomass over the last 20 years and it is likely to remain stable in the future. Management Moderate Stable A discards ban is being implemented under the CFP and thus there is some uncertainty on how this will impact fisheries management in the North Sea. There is concern over the use of a combined TAC for the two species, dab and flounder, which carries the risk of one of the species being overexploited. Bycatch High Improving Bycatch of non-target species in this fishery is relatively high with poor selectivity. However, with technical and spatial management measures continuously under development and the incoming EU landings obligation intended to reduce discarding of managed species, the bycatch risk is likely to reduce in the future. Habitat Moderate Improving Otter trawls have the potential to affect seabed habitats, but spatial management measures are continuously being developed and will likely reduce the risk. As planned networks of Marine Protected Areas become established, larger areas of sensitive habitat will become protected from trawling.

3 Stock Status Details less risk more risk Time-trends Landing data, shown in figure 1, has fluctuated around tonnes and shows a declining trend since the late 1990 s however they are not complete and are not indicative for catches since discard rates are substantial, around 91% for particular metiers (ICES, 2015) and only estimated for the last three years. The quarter one survey index of biomass is variable without trend with the last two years being the highest of the time-series. Figure 1. Dab in Subarea 4 and Division 3.a. Summary of the stock assessment. Top left: official landings ( ) and ICES estimates of landings and discards ( ). Top right: relative recruitment (age 1). Lower left: relative fishing pressure. Lower right: relative spawning stock biomass. Dashed lines indicate the average biomass index of the respective year range. Shaded areas in Z and SSB and error bars in R show 90% confidence intervals (ICES 2017). Stock structure and recruitment The number spawning grounds and the wide distribution of dab indicate the presence of more than one stock. Meristic data (Lozán 1988) corroborate the hypothesis of several stocks of dab, distinguishing significantly between populations from western British waters, the North Sea and the Baltic. Data gaps and research priorities Dab in Subarea 4 and Division 3.a. was benchmarked in 2016 (ICES, 2016a). Spawning stock biomass (SSB) is now estimated with a survey-based assessment model, taking into account available age and weight data from three beam trawl surveys ( , Q3). The downward trend in fishing mortality estimated by the assessment mirrors that observed in other stocks (plaice and sole) caught by the same fleets. It is expected that the downward trend is seen in all bycatch species from these fleets, supporting the results of the assessment. References ICES Report of the Working Group on the Assessment of Demersal Stocks in the North Sea and Skagerrak (WGNSSK), 28 April-7 May ICES CM 2015/ACOM:13 ICES. 2016a. Report of the Benchmark Workshop on North Sea Stocks (WKNSEA), March 2016, Copenhagen, Denmark. ICES CM 2016/ACOM: pp. ICES Dab (Limanda limanda) in Subarea 4 and Division 3.a (North Sea, Skagerrak and Kattegat). Published 30 June 2017 Lozán J.L., Verbreitung, Dichte, und Struktur der Population der Klieschen (Limanda limanda L.) in der Nordsee mit Vergleichen zu Popualtionen um Island und in der Ostsee anhand meristischer Merkmale. Arch. Fischereiwiss. 38:

4 Management Details less risk more risk TAC Information Catch 2016 (t) Advised Catch 2017 (t) Agreed TAC 2017 (t) Advised Catch 2018 (t) No TAC is set <64452 Advised and agreed catches Dab is mainly a bycatch species in the demersal fisheries for North Sea plaice and sole and has high discards. Landings data prior to 1998 are not complete and are not indicative of catches. Discards were estimated for the years Discard information was available for the most important fisheries, but discard values had to be raised in some cases. This procedure may introduce uncertainty in the estimation of total catch, given the extremely high proportion of discards in the catch (91%). Furthermore, survival rates of discards are unknown (ICES 2017). ICES was requested to assess the risk to the stocks of dab and flounder of having no catch limits for these stocks (ICES, 2017a). ICES advised that the risk of having no catch limits for the stocks of dab and flounder is currently considered to be low and not inconsistent with the objectives of the Common Fisheries Policy (ICES, 2017a). The advice is valid as long as dab and flounder remain largely bycatch species, with the main fleets catching dab and flounder continuing to fish the target species (plaice and sole) sustainably within the FMSY ranges provided by ICES. Consequently, the combined TAC for dab and flounder for Subarea 4 and Division 2.a was removed by the European Commission Council Regulation (EU) 2017/595 in March (EU, 2017). During the benchmark the total catch was revised. Therefore, the advice this year is based on the average catch of the most recent three years and not on the recent advised catch. Stock harvest strategy Dab in Sub area IV and division IIIa is assessed biennially using a data-limited approach to provide an indication of stock size. The stock assessment is based on a timeseries of trends using the quarter one international bottom trawl survey and landings data. Discarding of dab is substantial for fleets where data is available (ICES 2015), however discard estimates are only available for and have now been included in the data limited stock assessment. Dab in Sub area IV and IIIa is managed under the EU Common Fisheries Policy (CFP) primarily through annual Total Allowable Catches (TACs) which are set for dab and flounder (Plathichthys flesus) combined, and have been set at t since ICES advises that TACs may not be the most appropriate management tool for a bycatch species, and that a combined TAC for dab and flounder may lead to the overexploitation of one of the stocks. Reductions in fishing effort associated with the long term cod management plan (Regulation (EC)1342/2008), and the sole and plaice long-term management plan (Council Regulation (EC) No. 676/2007), may have influenced dab catches and fishing mortality. The increasing use of the more fuel-efficient SumWing beam trawl gear, and electric pulse trawls, may alter catchability and selectivity of fisheries for North Sea dab, though the effect has not yet been quantified. Potential future impact either on the dab stock itself or the stock assessment is unknown. Surveillance and enforcement Fisheries that catch dab in Sub area IV and IIIa are carried out by nine countries, and surveillance activities to record compliance with national and international fishery control measures are primarily the responsibility of the competent fishery inspection authorities in each country. In addition, the European Fisheries Control Agency (EFCA), established in 2005 ( ), organises operational coordination of fisheries control and inspection activities by the Member States as well as cooperation with third countries and other Regional Fishery Management Organisations. The requirements for surveillance and sanctions for infringements are laid down in the EU Control Regulation (EC) No 1224/2009. Surveillance activities on fisheries for turbot in Sub area IV include the use of vessel monitoring systems (VMS) on vessels over 12m overall length, an electronic reporting system (ERS), and a vessel detection system (VDS). Surveillance may also include direct observation by patrol vessels and/or aerial patrols, inspections of vessels, gear, catches at sea and on shore, and verification of EU logbook data against sales documents. The EU Control Regulation specifies that Member States should set up electronic databases containing the inspection and surveillance reports of their officials as well as records of infringements. References ICES Report of the Working Group on the Assessment of Demersal Stocks in the North Sea and Skagerrak (WGNSSK), 28 April-7 May ICES CM 2015/ACOM:13 ICES Dab (Limanda limanda) in Subarea 4 and Division 3.a (North Sea, Skagerrak and Kattegat). Published 30 June 2017

5 Bycatch Details less risk more risk Targeting and behaviour Demersal otter trawls operating in the North Sea (Sub-area IV) and eastern English Channel (Division VIId) can be towed by a single boat as a single or multiple rig. The trawl doors create sand clouds that herd the fish into the net. Otter trawls can be rigged with different types of ground gear depending on seabed topography and the species targeted (Løkkeborg, 2005). Demersal otter trawling is not a well targeted fishing activity given that a wide variety of non-target species can be caught. This fishery catches a wide variety of mixed demersal finfish, such as sole (solea solea), whiting (Merlangius merlangus), and plaice (pleuronectus platesa) and these mixed catches means that the minimum cod end mesh size of 80 mm and other aspects of the management regimes and markets are not optimal for all the species caught. Fish may be discarded because they are smaller than the Minimum Conservation Reference Size, or the size and/or species are not marketable. Discarding due to the vessel being short of quota for the managed species also occurs. Evidence of bycatch risk Discard rates have been estimated from surveys at around 30-40% of total catch weight in European demersal otter trawl fisheries (European Commission, 2011). According to the Discard Atlas for North Sea (Anon, 2014a) the main managed species discarded ( ) in the North Sea are species such as: dab (97%), plaice (77%), haddock (59%), cod (56%), and whiting (51%) by weight. There are high rates of discards for individual species, the total proportion of discards for the Greater North Sea in this fishery is around 41%. In addition, common skate (Dipturus batis) and spurdog (Squalus acanthias) can be taken as bycatch. Currently landings of these species is prohibited and fishermen are required to return them to the sea where they have a chance of survival. However, catch composition and discard rates vary according to regional variations in species composition, the design of the trawl, the cod-end mesh size and other selectivity devices used (see mitigation measures). Mitigation measures A wide variety of non-target species are caught in European mixed otter trawl fisheries. Optimising gear selectivity in mixed fisheries is challenging given that different species have different selectivity requirements. Many measures have been designed and tested over recent years, designed to increase selectivity in otter trawls. To actually be effective in controlling bycatch levels in fisheries, these measures have to be operationally viable, enforceable and used within an incentive scheme which encourages fishers to use them. The cod recovery plan (EU 1342/2008) which is in force in North Sea, Eastern English Channel, Irish Sea, West of Scotland and the Skagerrak, has encouraged a diversity of measures to incentivise the use of more selective gear by vessels targeting whitefish with demersal otter trawls. Effort per vessel is limited to a number of days at sea per year. Additional days at sea are available for vessels using certain specified gears and measures, tested for their efficacy at improving selectivity. The different European Nations have implemented different measures in their fisheries, described below are measures implemented in the UK fisheries. Fully documented fisheries scheme The fully documented fisheries scheme, which participating vessels (representing 27% of landings in 2012) use independent electronic monitoring devices (video recordings which monitor fishing activities) to ensure that all caught fish are recorded, and all caught cod are retained onboard, landed and count against quota (including undersized fish). In return, these vessels are allowed additional quota and days at sea, though they have to stop fishing when they use up their quota. By this means the total mortality on the cod stock is capped, wasteful discarding is reduced, and improved information on catches is available. Moreover, there is more flexibility for fishermen to use the additional days at sea up to the point when they run out of quota, and there is an incentive to use more selective gear in order to target more marketable fish. Since cod grow to a relatively large size compared with other species before they are marketable, the scheme benefits the selectivity of fishing on other fish in the catch thereby helping to reduce the overall discards. So far the scheme has not been in force long enough to fully evaluate the results, but it an illustration of the way in which measures to reduce discards can be incorporated into the overall management of the fishery thus increasing efficacy and incentives. Real time closures The cod avoidance plans also include real time closures of areas where concentrations of cod are found. Since 2007 UK administrations have operated these areas for UK vessels in the North Sea and English Channel in response to concentrations of juvenile cod; when a vessel catches more than threshold number of cod per hour agreed by a boarding officer and the skipper or concentrations of adult cod through analysis of landings and Vessel tracking data (VMS). The size and duration of the closure varies according to administrative body. This a similar scheme to designed operated under European legislation (EU 783/2011) which is designed to protect juvenile cod, saithe, haddock and whiting and there are also seasonal closures to protect spawning stocks (See Marine Scotland and Marine Management organisation websites). It has proved difficult to quantify the efficacy of each of these measures, however it seems likely that cod avoidance measures have contributed significantly to the reduction in the discard rate of cod in the North Sea fishery (Anon, 2014). Landings obligation The introduction of the landings obligation or discard ban under the EU Common fisheries policy (EU 1380/2013) is intended to take place over the period in

6 this fishery. This landings obligation will ultimately apply to all species managed by TAC; it will not apply to non-tac species, however many of these are likely to benefit from improved selectivity. References Anon Prepared by Scheveningen group, Discard Atlas of the North Sea Fisheries, August 2014, 80 pp. Løkkeborg, S. (2005). Impacts of trawling and scallop dredging on benthic habitats and communities. FAO Fisheries Technical Paper 472. Food and Agriculture Organisation of the United Nations, Rome, 58 pp.

7 Habitat Details less risk more risk Gear effects, targeting and behaviour Fishermen use their knowledge of seasonal fish aggregations and seabed types together with information from the vessel s electronic mapping tools to make informed decisions on where to trawl. Gears are adapted to the substrate type and the species targeted, with a relatively narrow range of conditions in which they can operate. Most otter trawling occurs within core areas where yields are high and it is safe to trawl, typically historically fished grounds (Jennings and Lee, 2011). Risk of habitat impact Otter trawl impact risk on the seabed habitat can include modification of bottom topography and disturbing biogenic features. Biological communities can potentially be disturbed both directly and indirectly by changes in the physical attributes of the areas being fished. Trawl doors have the most pronounced impacts on seabed habitats by creating scouring marks and furrows up to 20 cm deep (Løkkeborg, 2005). The habitat risks are related to the types of seabed communities and other sources of seabed disturbance such as wave and tidal action. A number of theoretical and field studies have focused on the effects of towed gears, which show that areas outside core fished areas tend to be more sensitive to fishing (Grey et al., 2006; Jennings et al. 2012). Consequently, habitats that have not traditionally been disturbed by fishing activities are relatively more sensitive to the effects of otter trawling. However, TR2 gears predominate in shelf waters for plaice, sole and dab which occupy habitats subject to relatively high levels of natural disturbance (due wave and tidal action). The impacts of TR2 gears on habitats is therefore less significant than the potential impacts of TR1 gears which operate in deep water muddy habitat environments. Understanding the nature of these differences is important in the management of the effects of otter trawling. Communities that inhabit areas where there is more disturbance by wave and tidal action are less likely to be affected by trawling, whereas communities inhabiting deeper waters unaffected by disturbance from wave and tidal action or on harder more gravely substrate are relatively more sensitive to trawling (Bolam et al., 2014). However, there are some habitats such as ross worm (or sabellaria) which inhabit shallower areas which are considered relatively sensitive, but such areas are traditionally avoided by TR2 fisheries. In the North Sea, demersal otter trawlers have reduced the biomass and production of bottom-dwelling organisms (Hinz et al., 2008; Hiddink et al., 2006). Sustained fishing has resulted in a shift from communities dominated by relatively sessile, emergent and high biomass species to communities dominated by infaunal, smaller bodied organisms (Kaiser et al., 2000). Within the core area of this fishery where the substrate is mostly sandy or muddy sand the risks of further ecosystem change due to fishing are minimised because the area has been continually heavily fished so the sea bed ecosystem has adapted to the fishing pressure. However, outside the core area of fishing there is the potential for significant habitat impact.. The fishery generally targets relatively shallow areas which are expected to be subject to wave and tidal action and hence relatively resilient to the effects of fishing. Fishing which has occurred in a specific location over many years is likely to result in the seabed ecosystem adapting to the fishing activity. However, there are sensitive areas, mostly outside the core areas of the fishery which may be vulnerable and such areas have in recent years been identified and protected to some extent through the Natura 2000 network of MPAs Mitigation measures Under the Marine Strategy Framework Directive (MSFD) from the European Union (Council Directive 56/2008), Member States have committed to aim towards good environmental status (GES) for the seabed habitats by The Convention for the Protection of the Marine Environment of the North-East Atlantic (the OSPAR Convention ), which was signed up to by 15 nations plus the European Union, is developing a coherent network of Marine Protected Areas to protect vulnerable marine habitats in the North-East Atlantic. The development of offshore Special Areas of Conservation under the European Habitats Directive (Council Directive 43/1992) contributes to this process as does the UK Marine Act and Marine Scotland Act designating Marine Protected Areas in UK waters. These initiatives have resulted in improvements in habitat mapping and risk assessment of the effects of trawling on the seabed, and the UK Marine Management Organisation (MMO) and Marine Scotland are engaging in a programme designed to assess the effects of fisheries and implement management measures where sites are considered at risk. References Bolam, S.G., Coggan, R.C., Eggleton, J., Diesing, M. and Stephens, D Sensitivity of macrobenthic secondary production to trawling in the English sector of the Greater North Sea: A biological trait approach. Journal of Sea Research 85: Gray, J.S., Dayton, P., Thrush, S. and Kaiser, M.J On effects of trawling, benthos and sampling design. Marine Pollution Bulletin 52: Hiddink, J.G., Jennings, S., Kaiser, M.J., Queirós, A.M., Duplisea, D.E, and Piet, G.J Cumulative impacts of seabed trawl disturbance on benthic biomass, production, and species richness in different habitats. Canadian Journal of Fisheries and Aquatic Sciences 63: Hinz, H., Hiddink, J.G., Forde, J., and Kaiser, M.J Large-scale responses of nematode communities to chronic otter-trawl disturbance. Canadian Journal of Fisheries and Aquatic Sciences 65: Jennings, S. and Lee, J Defining fishing grounds with vessel monitoring system data. ICES Journal of Marine Science 69: Jennings, S., Lee, J and Hiddink, J.G Assessing fishery footprints and the trade-offs between landings value, habitat sensitivity and fishing impacts to inform marine spatial planning and the ecosystem approach. ICES Journal of Marine Science 69:

8 Kaiser, M.J., Ramsay, K., Richardson, C.A., Spence, F.E., and Brand, A.R Chronic fishing disturbance has changed shelf sea benthic community structure. Journal of Animal Ecology 69: Løkkeborg, S. (2005). Impacts of trawling and scallop dredging on benthic habitats and communities. FAO Fisheries Technical Paper 472. Food and Agriculture Organisation of the United Nations, Rome, 58 pp. All content 2018 Seafish. Origin Way, Europarc, Grimsby, DN37 9TZ. This page created on 24th September 2018 at 08:25pm.