Crab, Velvet

Necora puber

Method of production — Caught at sea
Capture method — Pot or creel
Capture area — North East Atlantic (FAO 27)
Stock area — Scotland
Stock detail

All areas


Picture of Crab, Velvet

Sustainability rating four info

Sustainability overview

The Scottish velvet crab fishery has expanded relatively recently. Velvet crabs traditionally were caught as bycatch and subsequently discarded, as they were considered pests. After the Spanish fishery collapsed in the early-1980s, due to overexploitation and disease, southern European markets demanded velvet crabs from other fisheries. The French market served as an alternative until 1984, when their velvet crabs were infected by the dinoflagellate Hematodinium spp. which makes crab flesh pink and taste bitter.

The UK and Irish markets now fulfil these roles with mixed success. Velvet crab landings occur mostly in ICES division 6a (42%) and 4a (35%); mainly caught in inshore Scottish creel fleets. Very few landings are caught offshore. Landings in Scotland increased from 2002. In 2009, 2,300 tonnes of velvet crab were landed into Scotland, valued at 6.2 million pounds: Orkney, South Minch and the Hebrides (accounting for 65% of landings in 2013-15) are the three main fisheries although the two latter areas have exhibited a marked decrease over the last ten years. Very few fishermen target ‘velvets’ solely; they are landed between July and November.

A stock assessment has recently been conducted for velvet crabs in Scotland, which has evaluated stock indicators for six out of 12 assessment areas. Whilst biomass remains unknown, there is concern for fishing mortality on most of the assessed stocks. Marine Scotland recommends that a long-term reduction in effort would probably increase the yield and biomass-per-recruit in these assessment areas.

Velvet crab landings increased gradually until the mid-1990s, declining slightly up to 2005, followed by a sharp increase in 2006. Landings have since decreased to 1,500 tonnes in 2015. The reason for these trends is unknown. Males dominate landings (65% to 72% (by number), potentially attributable to differences in catchability.

Biology

The Velvet crab is part of the Portunidae (Swimming crabs) family. Itas found in north-west Europe from Norway to the Shetlands and south to Spain and the Canary Isles and in the Mediterranean off the coast of Malta. It inhabits rocky substrates, down to depths of 25m. They donat appear to migrate very far: movements are restricted to a few hundred metres. They are a fast moving and aggressive species, feeding mainly on brown algae.

Velvet crabs generally live up to four to six years old and reach sexual maturity around 40 mm (1.5 years), varying with location. In the Shetlands, males mature at 45mm and females 56mm. They produce between 5,000 and 278,000 eggs per female. Females grow more slowly and to smaller sizes than males. Males mainly moult between April and July and females moult between May and August. Mating occurs after females have moulted.

Stock information

Criterion score: 0.75 info

Stock Area

Scotland

Stock information

The stock status of velvet crabs is currently unknown as there are no reference points to determine the health of the stock. There are also no biomass indicators. Fishing mortality indicators show mixed results.

Velvet crab in the Clyde, East Coast, Orkney and South Minch, were fished at unsafe levels, above the reference point of fishing mortality at FMSY (both males and females). In these areas, velvet crabs are estimated to be growth overfished. There is concern for the stock in Orkney, South Minch and East Coast.

In the Hebrides, the estimated fishing mortality was found to be relatively stable over the time series. Fishing mortality for males was estimated to be below FMSY while females were fished above FMSY. The mean size of the largest males increased in recent years.

In the South East, males were fished at FMSY while females were fished above FMSY. No assessments were performed for the Mallaig, North Coast, Papa, Sule and Ullapool as the sampling data collected were considered insufficient to run the required assessments.

There is no vulnerability or resilience status for the velvet crab on Sealifebase, however, the species is not considered to be particularly vulnerability.

Management

Criterion score: 0.5 info

A new suite of measures have been implemented in light of new advice. However, the effectiveness of these at limiting fishing pressure is unknown. Since the velvet crab on the East coast, West coast and Orkney is currently fished at levels above the FMSY proxy, Marine Scotland have recently increased the minimum landing size to 70mm carapace width, prohibited the landing of berried velvet crab and matched landing restrictions to sale and carriage restrictions. However, crab and lobster fisheries are not subject to EU TACs or quotas.

In Scottish waters, vessels targeting velvet crabs must have a licence with a shellfish entitlement. There are no catch restrictions for vessels with a licence. Vessels that are over 10 metres in length with a shellfish entitlement licence are required to record all lobster and crab landings through a form and an EU logbook.

Since April 2017, vessels not holding a shellfish entitlement licence are limited to catching 5 crabs of any species per vessel per day. The licence system is currently limited and no new licenses and entitlements are being issued.

Marine Scotland considers 12 assessment areas which it assesses and manages separately. Most areas are fished close to or above FMSY. If fishing mortality were reduced in the Clyde, East Coast, Orkney and South Minch, a higher yield and biomass per recruit could be obtained.

Capture Information

Criterion score: 0.25 info

Bycatch
There are no discard data but they are likely variable and can be high (>50% by number). Survival rates of invertebrates is usually high in pot fisheries, but the survival rates of velvet crabs can significantly increase when they are held for long periods. Escape gaps and mesh sizes of pots can allow smaller-sized individuals to escape prior to lifting pots and soft, berried, undersized or otherwise non-targeted may be returned alive.

In creels, bycatch generally includes crabs and lobsters, however, can occasionally catch fish such as cod, poor cod and rockling, which may be discarded or used as bait.

In pots, endangered, threatened and protected species may include leatherback turtles, birds and whales. Areas including the Sea of the Hebrides region, the Little Minch and east coast of Scotland off Angus are a relatively higher risk for entangling minke whales than other areas of Scotland such as Shetlands. Around half of the approximate dozen baleen whales appear to have died due to entanglement. One of the reasons for the lower level of incidence with whales in Scotland compared to the US and Canada is due to the amount and proportion of rope in the water: creels are set in leadersa, where 10-25 creels are attached on a rope and laid on the seafloor. Whereas, in the western Atlantic, pots may only be laid in sets of threes which allow for a higher proportion of rope in the water column.

Habitat
Vulnerable features such as the sea pen (Pennatulacea), may be subject to some damage, but generally, creels present much less risk to the benthic habitats than other fishing gear such as bottom trawl or dredge.

To mitigate the risk of creels on the habitat, there is currently an ongoing process under the UK Marine and Coastal Access Act (2009) to map and manage habitats, aimed at coherent management taking into account their vulnerability to fishing.

References

Mesquita, C., Miethe, T., Dobby, H. and McLay, A. 2017. Crab and Lobster Fisheries in Scotland: Results of Stock Assessments 2013-2015. Scottish Marine and Freshwater Science Vol 8 No 14, 87pp. DOI: 10.7489/1990-1

SSMO Shetland inshore brown & velvet crab and scallop fishery

Marine Scotland. 2018. Velvet Crab. Available at: https://www.gov.scot/Topics/marine/marine-environment/species/fish/shellfish/VelvetCrab. [Accessed 8th June 2018].

Marine Scotland. 2017. POLICY NOTE: THE SPECIFIED CRUSTACEANS (PROHIBITION ON LANDING, SALE AND CARRIAGE) (SCOTLAND) ORDER 2017. SSI 2017/455. Available at: http://www.legislation.gov.uk/ssi/2017/455/pdfs/ssipn_20170455_en.pdf

ICES. 2013. Report of the Working Group on the Biology and Life History of Crabs (WGCRAB), 27-31 May 2013, Dublin, Ireland. ICES CM 2013/SSGEF:10. 83 pp

ICES. 2013. Report of the Working Group on the Biology and Life History of Crabs (WGCRAB), 27-31 May 2013, Dublin, Ireland. ICES CM 2013/SSGEF:10. 83 pp.

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

Wilhelm, G., & Mialhe, E. (1996). Dinoflagellate infection associated with the decline of Necora puber crab populations in France. Diseases of Aquatic Organisms, 26, 213-219

Wilhelm, G., & Mialhe, E. (1996). Dinoflagellate infection associated with the decline of Necora puber crab populations in France. Diseases of Aquatic Organisms, 26, 213-219