Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Witch sole, Northern stock, demersal trawl Witch sole, Northern stock, demersal trawl Content last updated 16th Feb 2017 Stock: Management: Overview Witch sole or witch flounder (Glyptocephalus cynoglossus), is a right-eyed flounder of the family Pleuronectidae which occurs on both sides of the Atlantic Ocean. The species is mainly found on soft bottoms, mostly clay or clean sandy bottoms between 100–400 m depth. The main diet consists of crustaceans, worms, brittle stars and fishes. Witch sole is typically a bycatch species, mostly captured in bottom otter trawls (88%) targeting whitefish (such as cod and haddock), or other flat fish species such as plaice, etc. It is also an important bycatch species in some Nephrop fisheries. Stock Status less risk more risk The status of the witch flounder stock in Subarea IV and Divisions IIIa and VIId (North Sea, Skagerrak and Kattegat, Eastern English Channel) has been scored a moderate risk. This is because the species has low resilience to fishing exploitation (FishBase, 2015) and the stock abundance has shown a marked increase in the last couple of years. No biomass or fishing mortality reference points have been defined for this data-limited stock, and therefore cannot be used to derive a risk score. Instead, a risk score was calculated using a data-limited approach where the low resilience of lemon sole to fishing exploitation was weighted by an increasing population trend. Management less risk more risk The management of witch flounder in Subarea IV (North Sea) and Divisions IIIa (Skagerrak–Kattegat) and VIId (Eastern Channel) has been scored a moderate risk. This is because data-limited approaches are used for setting management controls. No specific management controls have been established to restrict harvesting, and no stock-specific TAC has been defined by the European Commission. A TAC combining lemon sole and witch sole may not be an appropriate management measure to control the harvest rates of bycatch species. Bycatch less risk more risk The bycatch risk of witch flounder in Subarea IV (North Sea) and Divisions IIIa (Skagerrak–Kattegat) and VIId (Eastern Channel) has been scored a high risk. This is because demersal fisheries operating in these areas discard on average between 10 and 40% of the catch in weight. Demersal trawls are an active form of fishing gear that have the potential to take relatively high quantities of bycatch in certain circumstances. Habitat less risk more risk The habitat risk of this fishery has been scored a high-moderate risk. Although otter trawls are considered to have 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, of historically fished ground. However, 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 Type Current Risk Status Outlook Reason Stock Moderate Stable The status of the stock is likely to remain stable in the future given that no major changes in stock status are anticipated. Management Moderate Stable The management of the stock is likely to remain stable in the future. The CFP is going through reform and there is some uncertainty on how this will impact fisheries management in the North Sea, particularly due to the introduction of a landings obligation. Bycatch High Improving Bycatch in this fishery is relatively high. 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 High 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. Stock Status Details less risk more risk Time-trends Landings of witch sole increased from the mid 1960’s reaching an historical high in the early 2000’s. Landings declined thereafter, with evidence of an increase in the last 3 years. The abundance indices from the fishery independent International Bottom Trawl Survey (IBTS) survey show a declining abundance trend since the peak observed in 2000, followed by an increase in the most recent years both in landings and survey data (ICES, 2015). Fig. 1. Witch sole in Subarea IV and Division IIIa. Official landings (in thousand tonnes). Discards data have only been included since 2012. Biomass indices (kg.hr-1) from the IBTS survey in quarter 1 and quarter 3 estimated from the mature stock (all individuals larger than 34 cm.) Stock structure and recruitment Knowledge of witch sole’s stocks is based on old studies that identified two stocks in ICES divisions IIIa and IV, one in Kattegat and one in the North Sea and Skagerrak. However, considering that catches in Kattegat are small and scattered and that there is no firm evidence of spawning grounds in this area, witch sole is assessed by ICES as a single stock in Subarea IV, Division IIIa and VIId (ICES, 2013). In 2009, witch sole was included as a mandatory species in the EU Data Collection Framework (DCF). Accordingly, Denmark and Sweden started the regular sampling of biological data, i.e. length, weight, maturity status and age, in 3.a and 4 both in discards and landings. Scotland has also been collecting biological samples since 2009 but only from the landings. Data gaps and research priorities In order to perform an analytical assessment, information on stock structure, biological data and catch at age information would be needed. Survey indices are noisy because the survey is not designed for catching witch sole and catch per hour is too low for robust estimates (ICES, 2015). While age readings techniques are now well established, the macroscopic evaluation of maturity status is still uncertain. A project assessing gonad histology is under development and it is planned to be ready before the end of 2017 (ICES, 2016). A reliable analytical assessment will be possible when long time-series data are available. References ICES. 2013. Report of the Working Group on Assessment of New MoU Species (WGNEW), 18 – 22 March 2013, ICES HQ, Copenhagen, Denmark. ACOM. ICES. 2015. Witch (Glyptocephalus cynoglossus) in Subarea IV and Divisions IIIa and VIId (North Sea, Skagerrak and Kattegat, Eastern English Channel). ICES Advice Book 6.3.57 ICES. 2016. Report of the Working Group on the Assessment of Demersal Stocks in the North Sea and Skagerrak (WGNSSK), 26 April-5 May 2016, Hamburg, Germany. ICES CM 2016/ ACOM:14. 19 pp. Management Details less risk more risk TAC Information Catch 2014 (t) Advised Catch 2015 (t) 3107 Agreed TAC 2015 (t) Advised Catch 2016 (t) 3107 Advised and Agreed Catches Management of witch sole is conducted using a combined Total Allowable Catch (TAC) with lemon sole (Microstomus kitt) set for Division IIa and IV. The TAC for 2015 was set at 6391 tonnes. This combined species TAC might prevent effective control, as exploitation rates at species level are masked by combined catch rates and could potentially lead to overexploitation of either species (ICES, 2016). Witch sole is mainly a bycatch species in mixed fisheries and consequently, a TAC alone may not be appropriate as a management tool (ICES, 2016). ICES advises that in Subarea 4 and Divisions IIIa, IV, and VIId, when the precautionary approach is applied, catches of witch sole should be no more than 3107 tonnes for 2016 and 2017. Stock Harvesting Strategy Witch sole in Subarea IV (North Sea) and Divisions IIIa (Skagerrak–Kattegat) and VIId (Eastern Channel) is assessed biennially using official landings and survey data to estimate temporal trends in mature biomass. Witch sole is classified as category 3 Data limited stock. This category includes stocks for which survey indices (or other indicators of stock size) are available and provide indications of trends in stock metrics. Landings are monitored from EU logbooks and sales notes. Witch sole is managed under EU Common Fisheries Policy (CFP) through a precautionary Total Allowable Catch (TAC) together with lemon sole (Microstomus kitt). A lack of spatial overlap exists between the ICES assessment area and the management area in the North Sea. The assessment area covers a broader region (Subarea IV as well as Divisions IIIa and VIId) than the management area (Division IIa and Subarea IV). There is no official Minimum Landing Size (MLS) specified in EU waters. However, in most of the countries reporting catches the landing of witch below 28 cm is prohibited. Recent studies have estimated the size at which 50% of the stock is mature as 34 cm in length. Therefore, since 2015, the mature biomass indices are estimated based on specimens larger than 34 cm (ICES, 2015). In 2014, witch sole was included into the data call for WGNSSK 2014 and in 2015 this call was extended to obtain landing and discard data for the years 2012– 2015 from all countries. Surveillance and Enforcement Fisheries for witch sole in Subarea IV (North Sea) and Divisions IIIa (Skagerrak–Kattegat) and VIId (Eastern Channel) are carried out by a number of countries and surveillance activities to record compliance with national and international fishery control measures are primarily the responsibility of the 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 that take witch sole include the use of vessel monitoring systems (VMS) on board vessels over 12 m overall length; direct observation by patrol vessels and aerial patrols; inspection 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. 2015. Report of the Working Group on the Assessment of Demersal Stocks in the North Sea and Skagerrak (WGNSSK), 28 April-7 May, ICES HQ, Copenhagen, Denmark. ICES CM 2015/ACOM:13. 1229 pp. ICES. 2016. Report of the Working Group on the Assessment of Demersal Stocks in the North Sea and Skagerrak (WGNSSK), 26 April-5 May 2016, Hamburg, Germany. ICES CM 2016/ ACOM:14. 19 pp. Bycatch Details less risk more risk Targeting and behaviour Witch sole is typically a bycatch species, 88% of all witch sole is captured in bottom otter trawls targeting whitefish (such as cod and haddock), or other flat fish species such as plaice etc. It is also an important bycatch species in some Nephrops fisheries. In the North Sea the vast majority of witch sole landings in 2015 was reported by Denmark in Division IIIa using bottom otter bottom trawls targeting crustaceans (mesh size 90-119mm, TR1 and TR2 combined) and by Scotland in Subarea IV using otter bottom trawls targeting demersal fish (mesh size >=120 mm, TR1) (ICES, 2016). Demersal otter trawls operating in the North Sea and West of Scotland are 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. The functions of the ground gear are to ensure close contact with the bottom and to enable fishing on rough bottoms without damage to the trawl net. When targeting flatfish, a chain may be used as ground gear to chase the fish off the bottom. The trawl doors keep the trawl mouth spread open laterally and create the sand clouds that herd fish into the opening of the net (Løkkeborg, 2005). Larger mesh demersal otter trawling catches a variety of mixed demersal finfish, such at Atlantic cod (Gadus morhua), haddock (Melanogrammus aeglefinus) and saithe (Pollachius virens). Because of the nature of the mixed fishery, management measures which suit one stock may not be suitable for another captured in the same fishery. Evidence of bycatch risk Demersal fisheries operating in the North Sea discarded on average 40% of the catch in weight between 2010-2012. The average discard ratio for the years 2010-2012 in the Skagerrak was 23% and for the Eastern Channel between 10 – 40% of catches were discarded during the same time period (Quirijns et al, 2014). In 2014, witch sole was included into the data call for WGNSSK 2014 and since 2015 the data call was extended to obtain landing and discard data for the years 2012–2015. Estimated witch flounder-specific discard rates from 2012-2015 ranged between 10 and 30%. However, it should be noted that not all metiers were sampled in every quarter (ICES, 2016). Mitigation measures A wide variety of non-target species are caught in mixed European 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 fisheries these measures have to be operationally viable, enforceable and used within an incentive scheme which encourages fishermen to use them. This includes the introduction of 120 mm minimum mesh cod end sizes in the northern North Sea (North of 56°N) from 2002, which has helped to reduce the levels of discarding and increase selectivity in the fishery. 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 vessel. Additional days at sea are available for vessels using certain specified gears and measures, tested for their efficacy at improving selectivity. The ‘fully documented fisheries scheme’, in 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 counted 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. The total mortality on the cod stock is thus 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 other fish in the catch thereby helping to reduce the overall discards. The scheme has not been in force long enough to fully evaluate the results, but it provides an illustration of the way in which measures to reduce discards can be incorporated into the overall management of the fishery at increasing efficacy. 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 2016 – 2019 in this fishery. This 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 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 Quirijns FJ, Pastoors MA, Uhlmann SS, Verkempynck R. 2014. Discard Atlas of North Sea fisheries. IJmuiden: IMARES, prepared by the Scheveningen group. 84 pp. ICES. 2016. Report of the Working Group on the Assessment of Demersal Stocks in the North Sea and Skagerrak (WGNSSK), 26 April-5 May 2016, Hamburg, Germany. ICES CM 2016/ ACOM:14. 19 pp. Habitat Details less risk more risk Gear effects, targeting and behaviours Demersal otter trawls are designed to catch fish and shrimps that stay above the sea bed, from close to the bottom to several metres from the bottom (Løkkeborg, 2005). 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 environmental conditions in which they can operate. Most otter trawling therefore occurs within ‘core’ areas where yields are high and it is safe to trawl, typically historically fished grounds (Jennings and Lee, 2011). Evidence of habitat risk Demersal trawling causes physical disturbances on the sea bed, the extent of which will depend on the door weight and the sediment structure (Løkkeborg, 2005). Decreased habitat complexity has been suggested through the destruction of biogenic structures such as tubes and burrows (Schwinghamer et al, 1996). Otter trawls also remove, damage and kill seabed biota, can cause reductions in biomass, production and species richness (Jennings and Kaiser, 1998; Hinz et al, 2009), and ultimately can lead to substantial changes in benthic community structure (Kaiser et al., 2000). The severity of impacts are habitat and gear specific, the most severe impact occur when fishing on biogenic reefs composed of sessile epifauna trawled with heavy fishing gears. In the North Sea, demersal otter trawlers have reduced the biomass and production of bottom-dwelling organisms (Hinz et al., 2009; 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). Mitigation measures Under the Marine Strategy Framework Directive (MSFD) from the European Union (Council Directive 56/2008), the European nations have committed to aim for ‘good environmental status’ (GES) for the seabed habitats by 2020. 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 Special Areas of Conservation under the European Habitats Directive (Council Directive 43/1992) contributes to this process as does the UK Marine 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) is engaging in a programme designed to assess the effects of fisheries and implement management measures where sites are considered at risk. Similar initiatives are taking place in other European countries. References Gray, J.S., Dayton, P., Thrush, S. and Kaiser, M.J. (2006). On effects of trawling, benthos and sampling design. Marine Pollution Bulletin 52: 840–843. Hiddink, J.G., Jennings, S., Kaiser, M.J., Queirós, A.M., Duplisea, D.E, and Piet, G.J. 2006. Cumulative impacts of seabed trawl disturbance on benthic biomass, production, and species richness in different habitats. Canadian Journal of Fisheries and Aquatic Sciences 63: 721–736. Hinz, H., Prieto, V. & Kaiser, M.J. (2009). Trawl disturbance on benthic communities: chronic e ects and experimental predictions. Ecological Applications, 19, 761–773. Jennings, S. & Kaiser, M.J. (1998). The e ects of fishing on marine ecosystems. Advances in Marine Biology, 34, 201–352. Jennings, S., Lee, J and Hiddink, J.G. (2012). 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: 1053-1063. Kaiser, M. J., K. Ramsay, C. A. Richardson, F. E. Spence, and A. R. Brand. 2000. Chronic fishing disturbance has changed shelf sea benthic community structure. Journal of Animal Ecology 69:494–503. Rijnsdorp, A. D., Bastardie, F., Bolam, S. G., Buhl-Mortensen, L., Eigaard, O. R., Hamon, K. G. Hiddink, J. G., Hintzen, N. T., Ivanovic´, A., Kenny, A., Laffargue, P., Nielsen, J. R., O’Neill, F. G., Piet, G. J., Polet, H., Sala, A., Smith, C., van Denderen, P. D., van Kooten, T., and Zengin, M. (2015) Towards a framework for the quantitative assessment of trawling impacts on the seabed and benthic ecosystem. ICES J. Mar. Sci. 72, (9), doi: 10.1093/icesjms/fsv207. Schwinghamer, P., Guigné, J.Y. & Siu, W.C. 1996. Quantifying the impact of trawling on benthic habitat structure using high resolution acoustics and chaos theory. Canadian Journal of Fisheries and Aquatic Science, 53: 288-296. All content ©2017 Seafish. Origin Way, Europarc, Grimsby, DN37 9TZ. This page created on 17th June 2017 at 02:38am.