Crab, spider

Maia squinado

Method of production — Caught at sea
Capture method — Gill or fixed net
Capture area — North East Atlantic (FAO 27)
Stock area — UK
Stock detail

All Areas


Picture of Crab, spider

Sustainability rating four info

Sustainability overview

The common spider crab is one of several types which can walk forwards or backwards. The largest is the Japanese Spider Crab which can grow up to 3.7 m across (Around the size of a small car!).

Spider crabs are distributed is in the Celtic Sea and the Western Channel. The spider crab fishery is the second largest crab fishery in England and Wales. Within the UK, it is generally targeted along the South and West coasts. The fishery is very seasonal, generally occurring between April and August.

Their stock status is unknown and there are a lack of studies conducted on spider crabs. There is a lack of management in place to protect the species but management of the species tends to be better in inshore fisheries. These are fisheries which are managed by the Inshore Fisheries Conservation Authorities (IFCAs).

Creels and pots catch the majority of spider crabs caught. These pots are generally conventional crab pots with a slightly larger entrance to allow spider crabs (which are larger than edible crabs), to enter pots. The second most common gear type associated with their landings is gillnets. Spider crab are also caught as bycatch in brown crab and lobster pot fisheries. The spiny spider crab are the main target species for tangle net fisheries. Crab claws are also caught and landed as bycatch in mobile gear vessels.

If you choose to buy spider crabs, choose ones caught by pots or traps in inshore waters.

Biology

Spider crabs are generally only to be found on southern and western coasts of the UK, although there are increasing reports of commercial quantities of spider crabs occuring in Wales, Ireland and the Isle of Man. It is the largest crab found in British waters, with a carapace width of up to 20 cm and a leg span of 50 cm or more. Spider crabs inhabit coarse sand mixed grounds and open bedrock from the shallow sublittoral zone to a depth of 120 m, although highest densities occur between 0 and 70 m. Large migrations of spider crabs occur during the early spring when they move into shallower water to spawn. Female crabs become berried (egg-bearing) from April onwards, and by June all mature females are berried. Hatching occurs from July until November, following which the crabs migrate back to deeper water. It has a juvenile phase of up to three years, which is spent in shallow water close to the coast, with a predominance of small male spider crabs on rockier areas. A number of moults take place resulting in increases in size of up to 33% per moult, with males generally having the greatest increases in size. Males have an additional moult to the females, during which their chelipeds (claw bearing legs) reach their final size relative to the body. After the final, or terminal, moult occurs, M. squinado becomes fully mature and enters the adult phase of its life cycle when it starts breeding. After this terminal moult, the spider crab will not grow any larger, unlike edible crabs which will continue to grow throughout most of their life. This makes ageing of spider crabs very problematic, as individuals of the same age may be of different sizes. Carapace widths for mature adults are from 8.5 -20 cm for males and 7-17.5 cm for females. Spider crabs are known to congregate in large numbers and form mounds.

Stock information

Criterion score: 0.5 info

Stock Area

UK

Stock information

There is no stock assessment for spider crab and their stock status is unknown. There are no recent data to determine any biomass trends. Fishing mortality is unknown, though ICES catch data are available for the species, which show that landings have generally been stable between 2006 and 2010.

Management

Criterion score: 0.75 info

There are very few management measures in place to protect spider crab stocks.

The Undersized Spider Crabs Order 2000 mandates a Minimum Conservation Reference Size (MCRS) of 130 mm for male spider crabs and 120mm for females. Outside the 6 nautical mile limit, there is limited management beyond the MCRS. There is general management in place in English and Welsh pot and trap fisheries, which likely afford some protection to spider crabs. For example, vessels in shellfish fisheries require licences, there is limited entry for under 10m vessels, days at sea limit for over 15 metre vessels in the Celtic Sea.

There are no closed seasons, prohibitions for taking berried or molting crabs or maximum size limit in place. Management relating to trap requirements (e.g. trap size requirements, gear marking, biodegrable panels and escape vents) are dependent on the region. When spider crabs are landed in mobile gears, EC Technical Conservation Regulation No 850/1998 permits a maximum of 75kg of detached crab claws to be retained on board a fishing vessel and landed.

Further management has been implemented in some inshore fisheries: for example, Devon and Severn Inshore Fisheries Conservation Authority (IFCA) have increased the MCRS to 130mm for females and implemented an escape gap byelaw to protect undersized spider crabs and bycatch. Southern IFCA have implemented voluntary & funded escape gaps to reduce risk to undersized spider crabs and bycatch and are currently undertaking a study on bycatch in potting fisheries. The Lyme Bay Potting Study will also contribute to the better understanding of bycatch. The Fully Documented Fisheries project can improve information on landings (catch composition) of non-target retained species. <br
Monitoring
There are data gaps regarding the definition of the stock. Landings data are available from 1983 to 2010, though only limited effort data are available. Some size-frequency data exist between 2004 and 2010 and potentially some juvenile indices, however there is a lack of data available for the species.

Enforcement
Vessels above 12 metres in length are required to use Vessel Monitoring Systems (VMS). Logbooks are mandatory.

Capture Information

Criterion score: 0.75 info

The main target species of tangle nets are crabs. Tangle nets are not very selective and as it is difficult to remove spider crabs from tangle nets, they are often declawed and the claws are retained. Some regions use crab smashersa to more easily declaw the crabs from the nets. Declawing can result in tissue damage and haeomolymph loss. Injuries may be long-term as spider crabs donat moult once they reach full size, therefore the limb cannot regrow.

References

Northeastern IFCA. UK Fisheries Legislation. Primary Acts. Sea Fish (Conservation) Act 1967. Available at: http://www.ne-ifca.gov.uk/legislation-and-byelaws/uk-legislation/). [Accessed on June 7th 2018]

Marine Biological Association. 2017. Creepy Crabs. Available at: https://www.mba.ac.uk/creepy-crabs. [Accessed on June 8th 2018].

Seafish. 2018. Tangle nets. Available at: http://www.seafish.org/geardb/gear/tangle-nets/

The Welsh Government. 2002. WELSH STATUTORY INSTRUMENTS: The Undersized Spider Crabs (Wales) Order 2002. 2002 No. 1897 (W.198). Available at: http://www.legislation.gov.uk/cy/wsi/2002/1897/made

Seafish. 2016. MSC Pre-Assessment for UK Southwest lobster. Available at: http://www.seafish.org/industry-support/fishing/project-uk/project-uk-fisheries-improvements/southwest-crab-lobster-pot-fip

MMO. 2016. Landings data: 2012 to 2016.

Devon and Severn IFCA. 2017. Minimum Sizes for Fish and Shellfish. Available at: https://secure.toolkitfiles.co.uk/clients/15340/sitedata/byep/Minimum-Sizes-for-Fish-and-Shellfish.pdf

ICES. 2012. Report of the Working Group on the Biology and Life History of Crabs (WGCRAB), 14-18 May 2012. ICES CM 2012/SSGEF:08 80pp

Scottish Government. 2018. The Specified Crustaceans (Prohibition on Landing, Sale and Carriage) (Scotland) Order 2017. 2017 No. 455. Available at: http://www.legislation.gov.uk/ssi/2017/455/made

Woolmer. A., Woo, J., Bayes, J. 2013. Review of evidence for best practice in crustacean fisheries management in Wales. Available at: http://fisheries-conservation.bangor.ac.uk/documents/CrustaceanBylawReviewEvidenceReportFinal.pdf

Wilson, E. 2008. Maja squinado. Common spider crab. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme [on-line]. Plyymouth: Marine Biological Association of the United Kingdom. Available from: http://www.marlin.ac.uk/speciesinformation.php?speciesID=3761