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Spider crab off UK coasts, pots and traps

fish

Maja brachydactyla

Content last updated
18th Apr 2016

Stock:
Spider crab off UK coasts

Management:
EU and local Inshore Fisheries and Conservation Authorities

Overview

The spider crab (Maia brachydactyla) is a very large species of crab with a circular, convex carapace which is bordered by strong tapering spines. It is red, brownish-red, or yellowish in colour and the body can grow up to 20 cm long and is often covered with attached algae. Spider crab are found on coarse sand mixed grounds and bedrock on the open coast, and also in deep tide pools and shallow sublittoral. Within the UK, they are predominately found in the west and south-west coasts (Wilson, 2008).

The name change from Maja squinado to Maja brachydactyla follows studies which concluded that Maja squinado was in fact a separate species with a more southerly distribution.

Unlike crabs and lobsters spider crabs cease growing once maturity is reached (known as terminal moult). Spider crabs feed opportunistically, behaviour at least partly enforced by seasonal migrations that they perform. During the autumn and winter months, adults are usually found in offshore locations, usually between 40m and 80m depth (occasionally down to 120m). During the spring and summer, they are found further inshore usually in depths less than 10m and occasionally even in tidal water. Females may spawn up to twice in any one season and at 2-3 weeks the larval stage is shorter than for crabs and lobsters.

 

Fisheries

Spider crab is the subject of commercial fishery, with over 5,000 tonnes caught annually, more than 70% of it off the coast of France, over 10% off the coast of the United Kingdom, 6% from the Channel Islands, 3% from each of Spain and Ireland, 1% from Portugal, although official production figures are open to doubt.

In the UK this species is targeted on the South and West coasts using conventional crab pots but with a slightly larger entrance to allow this relatively large crab to enter the pot, and also with large mesh tangle nets. Based on a five year average, creels/pots land the majority of the catch (87% by weight), followed by gillnets (11%). It is very seasonal occurring during the period April to August.

 

References

Wilson, E. 2008. Maja squinado. Common spider crab. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 24/08/2012]. Available from:   http://www.marlin.ac.uk/speciesinformation.php?speciesID=3761

Stock Status

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Spider crab off UK coasts has been scored a high risk. There are difficulties of finding an easily monitored and reliable indicator of stock status so abundance trends are unknown. Growth rates are uncertain but the minimum conservation reference size (minimum landing size) is potentially instrumental in conserving spawning stock.

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Management

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The management of spider crab off West and South west UK coasts has been scored a moderate risk. This is because the management control in place, the minimum conservation reference size (minimum landing size), is rational in relation to the life-history of the species. Whilst this measure is enforced there is no monitoring of stock status.

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Bycatch

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The bycatch risk of this fishery has been scored as low risk. This is because significant discarding of undersized spider and undersized bycatch of edible crabs and lobster occurs, but these are released alive on hauling and survival rates are believed to be high. Catch of protected, endangered and threatened species is minimal. “Ghost fishing” by lost pots is not considered to be a problem.

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Habitat

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The habitat risk of this fishery has been scored as low risk. This is because evidence suggests fishery impact on the bottom is restricted to some abrasion caused by dragging pots and anchors during hauling and tide and wave action (Grieve et al., 2014).   The static gear used to prosecute the fishery is in contact with the bottom, but unlikely to have significant interaction with vulnerable habitats. Vulnerable marine habitats are protected within Convention for the Protection of the Marine Environment of the North-East Atlantic (OSPAR, 2013) and any kind of fishery there might be controlled if deemed necessary.

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Outlook

Type Current Risk Status Outlook Reason

Stock

Management

Bycatch

Habitat

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