Platichthys flesus

Method of production — Caught at sea
Capture method — Beam trawl
Capture area — North East Atlantic (FAO 27)
Stock area — North Sea
Stock detail — 3a, 4
Picture of Flounder

Sustainability rating three info

Sustainability overview

Updated July 2019

Flounder is mainly a bycatch species in bottom trawl fisheries for North Sea plaice and sole and is considered underutilised. They are mostly discarded due to their low commercial value and poor market demand, with discard rates being 29% of the total catch over the last three years. Flounder is a data limited stock and reference points have not been defined, but the latest stock assessment indicates that overfishing is not occurring (below FMSY proxy) and the biomass is stable. Flounder and dab previously had a combined total allowable catch (TAC), but this was recently removed following ICES advise indicating the risk of having no catch limits for the dab and flounder stocks was considered to be low and not inconsistent with the objectives of the Common Fisheries Policy (CFP). ICES stated this advice was valid as long as dab and flounder remained 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. If this situation changes this advice would need to be reconsidered. Beam trawlers interact with the seabed and can modify bottom topography and cause damage and removal of some biogenic features including vulnerable marine habitats and benthic communities.


A widespread European fish found in both fresh and marine water. Flounder is a coastal species that divides its life cycle between brackish and freshwater habitats. It moves offshore into deeper water of higher salinity in winter where it spawns in the spring. Spawning takes place at depths of 20-50 m in the southern North Sea from February to May. Males become sexually mature when 2-3 years old (20-25 cm) and females when 3-4 years old (25-30 cm), but in the northern part of the range this may occur some 1-2 years later. After spawning they migrate to inshore and sometimes brackish waters. The shallow coastal zone, and in particular the Wadden Sea, are important nursery areas. Like plaice, they spend most of the day buried in the sand, but become very active at night and move into shallower water to feed. Flounder attains a length of 50-60 cm and can live up to 15 years. The species feeds on a wide variety of invertebrates and fish in some areas.

Stock information

Criterion score: 0.25 info

Stock Area

North Sea

Stock information

Flounder in this region is a bycatch species and data limited stock and reference points have not been defined. The latest stock assessment undertaken in 2019 indicated that overfishing was not occurring (below FMSY proxy) and the biomass was stable. The International Council for Exploration of the Sea (ICES) have not been requested to produce catch advice for this stock so there is no scientific catch advice for future years provided. However, it is noted that so long as the species in the targeted fisheries for which flounder is a bycatch are exploited sustainably, there should be a low risk of flounder becoming overexploited. Catches in recent years have been around 2000 tonnes.


Criterion score: 0.5 info

Management of flounder in the North Sea is only partially effective. Flounder is a bycatch species in other flatfish fisheries for plaice and sole and is generally considered underutilised and is commonly discarded due to low market value and demand. As a bycatch species, management under the EU North Sea Multiannual Management Plan (NSMAP) for demersal stocks (2018) applies. The NSMAP aims to ensure that exploitation of living marine biological resources restores and maintains populations of harvested species above levels which can produce the Maximum Sustainable Yield (MSY) and that the precautionary approach to fisheries management is applied. Bycatch stocks do not have specific targets under the NSMAP but are supposed to be managed in accordance with the best available scientific advice and the precautionary approach when no adequate scientific information is available. However, MCS has concerns that the NSMAP is not being adhered to for all bycatch stocks, especially where adequate scientific advice is available.

Flounder was previously managed under a combined total allowable catch (TAC) together with dab, but this was recently removed following ICES advise indicating the risk of having no catch limits for the dab and flounder stocks was considered to be low and not inconsistent with the objectives of the Common Fisheries Policy (CFP). ICES stated this advice was valid as long as dab and flounder remained 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. If this situation changes this advice would need to be reconsidered. Catches have been below levels recommended in the past.

As flounder is not subject to catch limits, it does not fall under the EU landing obligation and nearly 30% of the catch has been discarded in recent years and there is no official EU minimum conservation reference size (MCRS).Flounder matures between 20-30cm though and some regional authorities do have minimum landing sizes in force.

The stock is data limited (ICES category 3) and the stock assessment is a survey trends-based assessment and there are no reference points defined. Discard information is only available for the years 2002-2018 for the most important fisheries. However, no reliable data on discards are available for beam trawlers targeting brown shrimp which may have had a significant impact on the stock.

Surveillance activities on fisheries for demersal stocks in the North Sea, Skagerrak and Kattegat and English Channel include the use of vessel monitoring systems (VMS) on vessels over 12m; direct observation by patrol vessels and aerial patrols; inspections of vessels, gear, catches at sea and on shore and requirements to record data in electronic logbooks (although vessels under 10m do not have to keep logbooks).

Capture Information

Criterion score: 0.75 info

Flounder is not commonly targeted commercially. It is taken as bycatch in fisheries for demersal and flat fish, mainly in beam trawl (77%) fisheries for plaice and sole with about 11% taken in otter trawl fisheries and 12% taken by other gear types.

Beam trawls have the potential to take relatively high quantities of bycatch (> 50% of catch weight) including sharks, skates and rays and occasionally protected, endangered and threatened (PET) species.

Beam trawls disturb seabed habitats and in the North Sea, beam trawlers have reduced the biomass and production of bottom-dwelling organisms. Sustained fishing within the core areas for this fishery are in relatively shallow areas of fine sand and sandy mud which are heavily fished. This has resulted in a shift from communities dominated by relatively sessile, emergent and high biomass species to communities dominated by infaunal, smaller bodied and faster growing organisms. The penetration depth of a beam trawl depends on sediment characteristics and varies between 1 cm and 8 cm. Trawls leave detectable marks on the seabed and the pressure exerted on the sea floor is strongly related to the towing speed, which is very high in flatfish fisheries as the gear itself is very heavy. The habitat risks are related to the types of seabed communities and other sources of seabed disturbance such as wave and tidal action. Within the North Sea, one of the more sensitive habitats that may be impacted by beam trawl is slow growing Sabellaria reef, frequently found in shallower areas of the southern North Sea. Further north, the large and very long-lived bivalve Arctica islandica (Ocean quahog), can also suffer damage in trawls. Some spatial management is in place but there remains a need to implement management measures in many designated marine protected areas (MPAs) to allow for the protection and recovery of these areas and sensitive designated features.

There are MPAs designated to protect seabed features from damaging activities in this region. The fishery overlaps with parts of these MPAs, but the proportion of the catch coming from these areas is expected to be relatively low in relation to the unit of assessment (i.e. less than 20% of the catch) and so these impacts have not been assessed within the scale of this rating. Given the important role that MPAs have in recovering the health and function of our seas, MCS encourages the supply chain to identify if their specific sources are being caught from within MPAs. If sources are suspected of coming from within designated and managed MPAs, MCS advises businesses to: establish if the fishing activity is operating legally inside a designated and managed MPA; and to request evidence from the fishery or managing authority to demonstrate that the activity is not damaging to protected features or a threat to the conservation objectives of the site[s].

The overall capacity and effort of the North Sea beam trawl fleet has been substantially reduced since 1995, likely due to a number of reasons, including effort limitations between 2008 and 2016 for the recovery of the cod stock. Fishing effort of the beam trawl fleet has shifted towards the southern North Sea to target sole over the past decade.


Based on method of production, fish type, and consumer rating: only fish rated 2 and below are included as an alternative in the list below. Click on a name to show the sustainable options available.

Halibut, Atlantic (Farmed)
Sole, Dover sole, Common sole
Turbot (Caught at sea)
Turbot (Farmed)


Engelhard GH, Lynam CP, Garcia-Carreras B, Dolder PJ, Mackinson S (2015) Effort reduction and the large fish indicator: spatial trends reveal positive impacts of recent European fleet reduction schemes. Environmental Conservation, 42, 227-236.

EU, 2019. Technical measures regulation. EU 2019/1241. Available at https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX:32019R1241 [Last accessed 13.09.2019].

EU, 2018. Regulation 2018/973 establishing a multiannual plan for demersal stocks in the North Sea and the fisheries exploiting those stocks. Available at https://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=CELEX:32018R0973&from=EN [Accessed on 02.07.2019].

EU, 2018. Commission Delegated Regulation (EU) 2018/2035 of 18 October 2018 specifying details of implementation of the landing obligation for certain demersal fisheries in the North Sea for the period 2019-2021. Available at https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=uriserv:OJ.L_.2018.327.01.0017.01.ENG [Last accessed 13.09.19].

FAO, 2001. Fishing gear types; beam trawls. Available at http://www.fao.org/fishery/geartype/305/en [Last accessed 23.09.19].

Hiddink, J., Jennings, S., Kaiser, M., Queiros, A., Duplisea, D. and Piet, Gerjan. 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 (2006) 4. 63. 10.1139/f05-266.

ICES, 2019. Flounder (Platichthys flesus) in Subarea 4 and Division 3.a (North Sea, Skagerrak and Kattegat). Available at http://ices.dk/sites/pub/Publication%20Reports/Advice/2019/2019/fle.27.3a4.pdf [Last accessed 23.09.19].

Lakkeborg, S. 2005. Impacts of trawling and scallop dredging on benthic habitats and communities. FAO Fisheries Technical Paper. No. 472. Rome, FAO. 2005. 58p.

Tillin, H.M., Hiddink, J.G., Jennings, S. and Kaiser, M. J., 2006. Chronic bottom trawling alters the functional composition of benthic invertebrate communities on a sea-basin scale. Marine Ecology Progress Series. Vol. 318. 31-45.