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

Tangle nets are the main fishing method used to capture spider crabs. Netting is less sustainable than potting, as with potting there is no by-catch of non-target species and small crabs may be returned to the sea alive. Avoid eating immature crabs below legal minimum landing size (120 mm maximum body width), egg-bearing crabs and fresh (not previously frozen) crabs caught during the spawning season (April-July). Cornwall currently offers the best choice for this species as fishing is by permit only and only spider crabs 130 mm and above may be landed within the district.

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

Stock Area

UK

Stock information

Spider crabs are found mainly along the southern and western coasts of the UK, although in recent years it appears that their range is extending northwards with increasing reports of commercial quantities of spider crabs occuring in Wales, Ireland and the Isle of Man. There is no stock assessment for this species. Stocks are thought to be abundant as they are not heavily fished, although reports are few and far between.

Management

Management measures for this species are currently confined to an EU Minimum Landing Size (MLS). For male spider crabs the UK has set a size of 130 mm. Females may be landed at 120 mm in accordance with EU requirements. Within the Cornwall Inshore Fisheres and Conservation Authority (IFCA) district, in both net and pot fisheries, fishing is by permit only. Under new regulations, introduced in 2011, all spider crabs landed within the district must measure at least 130 mm.

Capture Information

Tangle nets are the main fishing method used to capture spider crabs. Netting is a much less sustainable method of fishing for crab. Legs may become detached from the crab's body and non-target species may be caught and discarded. Nets, often lost on rough ground or wrecks, cause problems associated with littering and 'ghost fishing'. The minimum landing size for spider crab in EU waters is 120 mm (carapace width) with UK legislation imposing an additional MLS of 130mm carapace length for males.

References

http://www.cornwall-ifca.gov.uk/sitedata/Misc/CSFC_Spider_Crab_Report_20.pdf; http://www.cornwall-ifca.gov.uk/sitedata/Misc/Shellfish_Survey_Report_2.pdf;