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Crab, brown or edible

Cancer pagurus

Method of production - Caught at sea
Capture method - Creel or pot
Capture area - North East Atlantic (FAO 27)
Stock area - Scotland
Stock detail - Shetland
Certification - Marine Stewardship Council (MSC)
Fish type - Shellfish

Sustainability rating Click for explaination of rating

This fish, caught by the methods and in the area listed above, is a good sustainable fish to eat. Click on the rating icon above to read more and on the alternatives tab below to find similar fish to eat.


Sustainability overview

The SSMO Shetland inshore brown crab fishery is certified as a responsible fishery by the Marine Stewardship Council (MSC). Avoid eating crabs below the minimum landing size (13-14cm in most areas of the UK) and crab claws, unless it is certain they have been removed after landing. Egg-bearing or "berried" females should be avoided at all times to allow them to spawn.

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 100m. 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

Stock area
Scotland

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Stock information
The brown crab creel fishery off the northern coast of Scotland was for many years a predominantly inshore fishery. However, the last 20 years have seen a rapid expansion of the fishery and a move by some of the larger vessels to grounds further offshore (beyond the 12 mile limit), particularly the Sule and Papa Banks. In addition, in 2004, an area to the north west of Scotland (known as the Windsock) was closed to mobile gear with meshes over 55 mm as part of cod recovery measures. The Sule Bank which is situated within the Windsock is now particularly favoured by creel fishermen as their gear is spared the risks of damage or loss from associated trawling, and the fishing effort in the offshore fishery is concentrated in the area. 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. Assessments in the Sule area for the period 2006-2008 indicate levels of exploitation at or around FMAX, the level of fishing mortality associated with the maximum long term equilibrium yield, whereas those for the inshore areas indicate components of the stock are exploited above FMAX. Given the relatively recent expansion of the offshore fishery and the lack of information on stock dynamics, there are some concerns about the state of crab stocks. In addition, fishermen have questioned whether the inshore and offshore stocks to the north west of Scotland are linked or part of the same population, and how fishing in one area may affect the stock in the other.To address this question, Marine Scotland Science set up a tagging study to obtain information on migratory and life history patterns of brown crab to the north west of Scotland. Overall, the tag return rate was lower than anticipated and the numbers returned to date preclude detailed statistical analysis of all possible relevant factors. However, the study has provided evidence of significant movements of crab stocks, in particular movements of female crab from offshore to inshore areas and across the Pentland Firth. Through tagging studies carried out by NAFC Marine Centre and Marine Scotland the Shetland brown crab population can be considered as a stock unit discrete from wider populations.

Management

There are a range of measures available for the management of crab stocks including but not limited to: licensing; limited entry; closed seasons and areas; minimum and maximum landing sizes; prohibitions on landing of berried crabs, soft crabs or crab parts; use of crabs as bait; trap limits and size; use of escape vents; biodegradable panels; vessel size and power; and use of VMS or vessel monitoring systems, which may be introduced at the EU or national and regional or local level. A restrictive licensing scheme for shellfish was introduced in UK waters in 2004, and increased monitoring of landings and effort were introduced in 2006 for boats under 10m in length in all areas of the UK. EC legislation sets a minimum landing size of 130mm for crabs in the North Sea south of 56 degrees N. It also restricts the proportion of the crab landings which is detached claws caught by pots or creels to less than 1% by weight of total catch. A by-catch limit of no more than 75kg per day of crab claws taken by other gear types can be landed. National legislation restricts the number of shellfish licences available (in England and Wales) and also prohibits landing of berried and soft crabs. A derogation to the EC legislation sets an MLS of 115mm in the Eastern IFCA area. In coastal waters out to 6 miles, potting is regulated by a number of Inshore Fishery Conseration Authority (IFCA) byelaws. Measures to cap fishing effort include freezing existing pot numbers for each vessel and reducing pot efficiency for example. The view is that a ban on parlour pots would significantly reduce potting effort. There are no official management measures relating to brown crab except for those imposed by the Inshore Fishery Conservation Associations (IFCAs) within 6 miles of the coast. These measures include a limit on boat size to under 15 metres, Minimum Landing Size (MLS) and escape gaps in all soft eyed pots. Within the Devon and Severn IFCA an Inshore Potting Agreement prohibits trawling in a designated static-gear area off Start Point. Implemented in 1978 to restrict the use of towed gears in inshore areas that had traditionally been used by static-gear (pot and net) fishers the IPA is a zoned fishery management system covering some 500 square kms. Since 2002 the previous voluntary agreement is now enforced by Government legislation. Although established to reduce conflict between mobile and static fishing gears the closure has created positive environmental benefits such as increased biodiversity and abundance of benthic (bottom dwelling) species. Benefits to other fisheries are also well documented. For example increased fecundity of scallops in the no-trawl area provide more spillover spat to outside fished grounds. Fishermen fishing within the IPA are developing a voluntary code of conduct to promote their best practice.

Capture information

Pots are a highly selective method of fishing. Undersized animals can be returned to the sea alive.

Read more about capture methods


References
Scottish Statuatory Instruments 2009. No. 443. Sea Fisheries. The Shetland Islands Regulated Fishery (Scotland) Order 2009; The SSMO Shetland inshore brown and velvet crab, lobster and scallop report - MSC Public Certification Report. January 2012.; G Jones et al (2010) Brown crab (cancer pagarus) migrations off the Northern Scottish Coast. Scottish Industry Science Partnership Report 02/10.

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