Crab, brown or edible

Cancer pagurus

Method of production — Caught at sea
Capture method — Pot or creel
Capture area — North East Atlantic (FAO 27)
Stock area — Southern North Sea
Stock detail — 4c
Picture of Crab, brown or edible

Sustainability rating four info

Sustainability overview

Updated: November 2019.

This stock is data limited and the stock status is unknown. No data on recruitment in the Southern North Sea stock is collected and the fishery is assessed using UK landings from this stock unit only. Data are unsuitable for estimating stock size, but fishing mortality for both sexes was estimated to be above FMSY targets. Crab and lobster fisheries are not limited by EU Total Allowable Catch (TAC) regulations although there have been moves by the EU to restrict the fishing effort such as restricted kW days at sea for boats over 15m. A minimum landing size of 115mm carapace width is in place. Pot fishing is considered sustainable as it is selective for larger individuals and has minimal impact on the surrounding environment.

Biology

The brown crab is commonly found in the North Atlantic Ocean, North Sea, less so in the Mediterranean. It is the heaviest British crab and easily identified by a characteristic pie-crust edge to the carapace or shell. They are found in waters down to 100 m. Brown crabs are highly fecund. Mating activity peaks in the summer when the female has moulted with spawning occurring in the late autumn or winter. Egg carrying females are largely inactive over the winter brooding period before the eggs hatch in the spring and summer. Between 250,00 to 3,000,000 eggs are held by the female for 8 months until they hatch into planktonic larvae. After around five weeks in the plankton, the crab larvae settle on the seabed. Juvenile crabs settle in the intertidal zone and remain in these habitats for 3 years, until they reach 6-7 cm carapace width, at which time they migrate to subtidal habitats. The crab is encased in a hard, rigid shell, which, like other crustaceans, has to be shed at intervals to permit growth. Moulting takes place at frequent intervals during the first years of a crab’s life, but only every two years after it is grown and this is mirrored by a slowing of growth rate. Growth is dependent on the frequency of moulting as well as the increase in size on each moulting occasion and it typically takes about four or five years for a juvenile crab to grow to commercial size. They can grow up to about 25 cm carapace width, with the larger specimens inhabiting deeper water. Growth rate varies between areas, and animals will typically reach a minimum landing size of 140mm carapace width at 4 to 6 years old. Environmental variables e.g. sea temperature related to geographical area and fishing pressure affect the size of maturity with animals in more northerly latitudes growing and maturing more slowly. Minimum landing sizes vary around the British coast from 150mm in the Western Channel to 115 mm in Norfolk for example. Edible crabs can live for up to 100 years but average age is around 25 to 30 years, and sexual maturity is reached after approximately 10 years, but can be as early as 3 to 4 years. Female brown crabs in Scottish waters typically mature between 130 and 150 mm CW. In Orkney research has shown that sexual maturity can be reached at 115 to 120 mm. The sex of a brown crab can be determined by the shape of the abdomen; the males being narrow and the females being broad and rounded for carrying eggs. Stock boundaries for edible crab remain poorly understood and both sexes move quite widely at times; females in particular have been shown to travel large distances in relation to spawning activity.

Stock information

Criterion score: 1 info

Stock Area

Southern North Sea

Stock information

There is concern for both biomass and fishing pressure on the southern North Sea brown crab stock.

According to the most recent stock assessment, using data up to 2017, stock size is at the minimum reference point for males, and a little higher for females, although still below levels associated with Maximum Sustainable Yield. The exploitation rate is high, being above the maximum reference point for both males and females. There is no data available on recruitment in the Southern North Sea.

Genetic studies have demonstrated that while differences between brown crab populations are low, they are sufficient enough to show that there is a genetic distinction between crabs in the Channel, the UK coast of the North Sea, and the Swedish part of the North Sea. Stock boundaries for brown crab are poorly understood and both sexes move quite widely at times with females in particular being shown to travel large distances in relation to spawning activity. This stock represents just one of six Crab Fishery Units that have been defined for England and Wales. These units have been defined based upon knowledge of larval distributions and development, hydrographic conditions and the distribution of fisheries.

Management

Criterion score: 0.5 info

Fishing pressure is close to the upper limit reference point. There are permits, but no catch or effort limitations (e.g. pot limits). Management measures are insufficient to control fishing pressure or recover the stock.

Crab and lobster fisheries are not limited by EU Total Allowable Catch (TAC) regulations or national regulations, and therefore are not limited in the number of crabs they can take, although there have been moves by the EU to restrict the fishing effort. In many areas, market preference can also have influence on the crabs which are landed, as those having an unclean appearance, due to disease or discolouration, or those missing both claws can be seen as unmarketable.

The southern North Sea brown crab stock supports three distinct fisheries: the Holderness fishery off Yorkshire, and two Norfolk fisheries. Management of the Norfolk fisheries falls under the jurisdiction of Eastern Inshore Fisheries and Conservation Authority (EIFCA). To fish for crab and lobster in this district, you must hold a National Shellfish License, which restricts the entry of new vessels into the fishery and requires catch and effort information to be returned. EIFCA have set a Minimum Landing Size (MLS) of 115mm carapace width. In this region, this means that 96 - 99% of males will be sexually mature but only 60 - 86% of females will be sexually mature. In the UK, national legislation prohibits the landings of berried and soft crabs.

Capture Information

Criterion score: 0 info

In the UK, brown crab and European lobster are fished together in a mixed fishery with both being targeted, with seasonal and regional variation of target species taking place. The key fishing season for brown crab in the UK takes place from May to December. Crabs are caught in pots, also known as creels, and can be fished individually or as part of a fleet of up to 100 pots, depending on the size of the boat and crew. Pots are portable traps made up of wood or steel wire and plastic. The crab is baited into the initial part (the chamber) and moves into the secondary part (the parlour) where it becomes trapped.

Pot fishing is considered sustainable as it is selective for larger individuals and has minimal impact on the surrounding environment. In brown crab fisheries, there is no legislation or regulation to standardise the type of pot used. They tend to be highly selective as undersized animals can be returned to the sea alive and survival rates for non-target organisms are thought to be high. More than half of the bycatch caught are predicted to survive, although there is little available research to prove this. Measures to further reduce bycatch and environmental impacts include the use of escape panels to allow undersize animals and bycatch to escape pots.

References

ICES. 2018. Interim Report of the Working Group on the Biology and Life History of Crabs (WGCRAB), 8-10 November 2017, Brest, France. ICES CM 2017/SSGEPD:09. 30 pp. Available at https://www.ices.dk/sites/pub/Publication%20Reports/Expert%20Group%20Report/SSGEPD/2017/01%20WGCRAB%20-%20Report%20of%20the%20Working%20Group%20on%20the%20Biology%20and%20Life%20History%20of%20Crabs.pdf [Accessed on 15.11.2019]

ICES. 2017. Report of the Working Group on the Biology and Life History of Crabs (WGCRAB), 1-3 November 2016, Aberdeen, Scotland, UK. ICES CM 2016/SSGEPD:10. 78 pp. Available at http://www.ices.dk/sites/pub/Publication%20Reports/Expert%20Group%20Report/SSGEPD/2016/01%20WGCRAB%20-%20Report%20of%20the%20Working%20Group%20on%20the%20Biology%20and%20Life%20History%20of%20Crabs.pdf [Accessed on 15.11.2019]

Ondes, F., Emmerson, J., Kaiser, M. J., Murray, L. G. and Kennington, K. 2019. The catch characteristics and population structure of the brown crab (Cancer pagurus) fishery in the Isle of Man, Irish Sea, Journal of the Marine Biological Association of the United Kingdom, 99(1), 119-133. Available at https://www.cambridge.org/core/journals/journal-of-the-marine-biological-association-of-the-united-kingdom/article/catch-characteristics-and-population-structure-of-the-brown-crab-cancer-pagurus-fishery-in-the-isle-of-man-irish-sea/3B4BD24E7DFF1D55C57D5D6FC547275A [Accessed on 15.11.2019].

Seafish. 2013. Responsible Sourcing Guide: crabs and lobsters. Available at https://www.seafish.org/media/publications/SeafishResponsibleSourcingGuide_CrabsLobsters_201309.pdf [Accessed on 15.11.2019]

Cefas. 2017. Cefas Stock Status Report 2017: Edible crab (Cancer pagurus). Available at https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/722904/Cefas_Crab_Stock_Assessment_2017.pdf [Accessed on 22.11.2019].

Seafish. 2016. RASS Profile: Edible crab in the Southern North Sea, Pots. Available at https://www.seafish.org/risk-assessment-for-sourcing-seafood/profile/edible-crab-in-the-southern-north-sea-pots [Accessed on 22.11.2019].