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 — Scotland
Stock detail — Orkney
Picture of Crab, brown or edible

Sustainability rating three info

Sustainability overview

Updated: November 2019.

For this data limited stock, there is concern for biomass (owing to lack of any data) and concern for fishing pressure. Biological reference points are not available for the Orkney brown crab fishery. Landings of Orkney brown crab increased from 1,156 tonnes in 2009 to 2,463 tonnes in 2016, showing an increasing trend in recent years. Fishing mortality is estimated to have been above MSY for both males and females from 2006-2015. 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 such as restricted kW days at sea for boats over 15m. 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: 0.75 info

Stock Area

Scotland

Stock information

For this data limited stock, there is concern for biomass (owing to lack of any data) and concern for fishing pressure. Brown crab has a high resilience to fishing pressure.

Biological reference points are not available for the Orkney brown crab fishery. Total Scottish landings of brown crab fluctuated between 9,300 and 12,300 tonnes from 2008 to 2016, while in Orkney landings increased from 1,156 tonnes in 2009 to 2,463 tonnes in 2016. Fishing mortality on the Orkney stock is estimated to have been above MSY for both males and females from 2006-2015.

The principal fishing areas for brown crab in Scotland are the Hebrides, Orkney, Sule, East Coast, Papa and South Minch. Landings from these areas accounted for around 80% of the total in recent years. For assessment purposes, the Scottish creel fishing grounds are divided into 12 assessment areas. A key issue is that there is no straightforward way of ageing crabs and regional assessments of crab stocks around Scotland are currently based on length cohort analyses (LCA) and use reported landings data and market sampling length frequencies collected by Marine Scotland Science.

Management

Criterion score: 0.5 info

There are some management measures in place for this stock, and a voluntary code of practice, but fishing pressure has been above sustainable limits over the last 10 years and there are no catch limits to prevent overexploitation.

EU technical conservation measures include geographically varying minimum landing sizes (MLS). In Orkney, and throughout Scotland, this is set at 150mm. Orkney Sustainable Fisheries (OSF) Ltd was established in 2006 to take over the running of the local lobster hatchery and carry out shellfish research. Through OSF, the fishery undertook a 4-year fishery improvement project (FIP) with the aim of achieving MSC certification, but it was unsuccessful and is now neither certified nor in a FIP. To demonstrate OSF’s commitment to sustainable fishing, a Fisherman’s Code of Practice is in place, specifying best practice for fishing, handling and storage of shellfish. The Code of Practice requires that only hard shelled, heavy crabs in good condition are landed and that pre or post moult crabs, berried or egg-bearing females, crabs exhibiting ‘black spot’ disease, one-clawed crabs, or other visibly diseased crabs are not landed.

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.

In Scotland, vessels fishing commercially for brown, velvet, spider, or green crab, lobster or crawfish must have a license with shellfish entitlement. Owners of vessels that are 10m and under with a shellfish entitlement are required to complete the FISH1 form for all landings of crabs and lobsters and submit it on a weekly basis to the Fishery Office at which the vessel is administered. For vessels that are over 10m in length, data on fishing activity by trip must be recorded in an EU logbook and submitted to the Fishery Office within 48 hours of landing. Licensed fishing vessels that do not hold a shellfish entitlement can land a maximum of 5 lobsters and 25 crabs per day. New regulations, effective from April 2017, restrict the numbers of certain shellfish species that can be taken by unlicensed fishing boats. The restrictions are set daily per vessel as 1 lobster and 5 crabs (of any species). There is currently a restrictive licensing system, whereby no new licenses and entitlements are being granted.

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]

C Mesquita, T Miethe, H Dobby and A McLay. 2017. Crab and Lobster Fisheries in Scotland: Results of Stock Assessments 2013-2015 Scottish Marine and Freshwater Science Vol 8 No 14 Available at https://data.marine.gov.scot/dataset/crab-and-lobster-fisheries-scotland-results-stock-assessments-2013-2015/resource/80511417 [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].

The Specified Crustaceans (Prohibition on Landing, Sale and Carriage) (Scotland) Order 2017 Available at http://www.legislation.gov.uk/ssi/2017/455/contents/made [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]

Orkney Sustainable Fisheries Ltd. 2016. Draft Inshore Fisheries Management Plan. Available at http://www.orkneysustainablefisheries.co.uk/wp-content/uploads/2014/11/Approved-management-plan-Jan-2016.pdf [Accessed on 15.11.2019].