Crab, Velvet

Necora puber

Method of production — Caught at sea
Capture method — Pot or creel
Capture area — North East Atlantic (FAO 27)
Stock area — England, Wales and Isle of Man
Stock detail

All areas


Picture of Crab, Velvet

Sustainability rating three info

Sustainability overview

In the UK, velvet crabs traditionally were caught as bycatch and subsequently discarded, as they were considered to be pests. Velvet crabs are traditionally consumed by southern European nations, France and Spain. However, the populations in these areas significantly declined in the 1980as due to overexploitation and an infection, caused by dinoflagellate Hematodinium spp, called the Pink Crab disease where their meat turns pink and tastes bitter. Their declines in these regions resulted in a commercial development in UK and Irish spider crab fisheries.

This rating covers England, Wales and the Isle of Man because there is a lack of data regarding the stock in these areas.

Most of the velvet crab landings are exported, as there is no market for them in the UK. However, the scale of exports and imports is unknown. Very few fishers solely target velvet crabs, though there are a few target fisheries when velvet crabs are in abundance, at certain times of the year.

Pressure for the stock may further increase, as a 2016 study in the Bay of Seine has suggested that PCB and dioxin levels in velvet crabs are higher than European thresholds. Therefore, the ANSES (National Agency for Safety) have recommended that the consumption of velvet crab from this area to be forbidden.

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: 0.5 info

Stock Area

England, Wales and Isle of Man

Stock information

The stock status of velvet crabs is unknown and there are insufficient data to determine biomass trends. Therefore, there is concern for biomass. Since velvet crabs are a non-target species, they generally have high survival rates when discarded and their landings have declined over time, there is no concern for fishing mortality.

The stock status of velvet crabs is unknown; landings in England peaked in 2006, but have declined in recent years, which is attributed to a lack of marketing infrastructure and several cold winters occurring in a row, which has caused the population to decrease. Landings in 2012 were around 155 tonnes with a value of 213,400 pounds. Similarly, there has been a decline in landings in ICES area 7 between 2006 and 2016. Catch trends are highly variable, depending on market factors and velvet crab abundance. Since their catch rates are dependent on market factors, catch rates cannot be used as an proxy for abundance.

In the Isle of Man, there has been a long tradition of pot fishing. There is a commercial fishery for the velvet swimming crab, though they are not a primary target species. The main target species (mainly the brown crab and European lobster) are of a larger size, have a larger population size and have a higher economic value.

Management

Criterion score: 0.75 info

The main management measure to protect the species is a Minimum Conservation Reference Size (MCRS) of 65 mm carapace width, which is larger than the size at first maturity. Though there are studies to suggest that the MCRS should be higher to accommodate for breeding. Those which are discarded, generally have high survival rates. There are no catch limits though effort is controlled through the national shellfish licencing scheme. Vessels targeting velvet crabs must have a licence, though vessels which do not have a licence, are limited to landings a maximum of 25 crabs per day. These controls are not based on the velvet crabas stock status. br>
Surveillance and enforcement
Vessels fishing for velvet crabs must have a shellfish license. Vessels of a length 10 metres and under with a shellfish licence are required to report catches to Marine Management Organisation (MMO) on a weekly basis. Vessels above this size are required to their catches recorded through an EU logbook.

Within the 6nm limit, velvet crab fisheries are managed by the Inshore Fisheries and Conservation Authorities (IFCAs) in England and Devolved Government in Wales. Some IFCAs have implemented management measures in pot and creel fisheries to reduce their impact on bycatch and habitats, such as requirements to have escape gaps on pots, which likely protect velvet crabs, though these management measures are regional and there are few direct measures to protect the stock. Escape gaps have been shown to reduce the catches of most finfish and invertebrates by over 80%. Manx pots are fitted with escape gaps.

Capture Information

Criterion score: 0 info

Crab fisheries are usually prosecuted using creels or pots. Bycatch
In creels, bycatch is usually comprise of crabs, poor cod, starfish, cod or scallops, which can usually escape creels after days or weeks. Bycatch levels are likely to be low in the Isle of Man fisheries. Discards are unknown, however, invertebrates generally have high survival rates when discarded from pots or creels. Catches of Endangered, Threatened or Protected species are thought to be rare though otters and seabirds occasionally interact with pots and leatherback turtles and whales have very occasionally become entangled in pot ropes. Further studies are required to determine the true impact of the pot, trap and creel fishery on whales: around half of the near dozen stranded baleen whales every year in Scotland, have died due to entanglement.

There are some concerns over bait used in the pot fisheries, which can include Small spotted catshark Scyliorhinus canicula, ballan wrasse Labrus bergylta and European conger Conger conger.

Habitat
Creels and pots generally present a low risk to the habitat, compared to fishing methods such as bottom trawl or dredge and a previous study conducted off Lundy Island suggested that that there was no difference between areas fished using pots and those left unfished. There may be some, but minimal impacts on the sea pen (Pennatulacea). Habitat protection is important for velvet crabs as they have important habitat preferences during their plankton stage. Therefore, habitat protection may yield some protection to velvet crabs.

Ghost fishing in pot fisheries is considered to be low in the Isle of Man however, over 1000 pots are lost each each in the Welsh pot fishery.

References

ndes,F. Kaiser, M.J. Murray, L.G. 2017. Fish and invertebrate by-catch in the crab pot fishery in the Isle of Man, Irish Sea. Journal of the Marine Biological Association of the United Kingdom 199, 1-13.

Pantin J.R., Murray L.G., Hinz H., Le Vay L. and Kaiser M.J. 2015. The inshore fisheries of Wales: a study based on fishers ecological knowledge. Fisheries and Conservation report, Bangor University, no. 42, p. 60. Fish and invertebrate by-catch in the crab pot fishery in the Isle of Man, Irish Sea.

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

ICES catch data. Velvet swimming crab. 2006-2016

Mclay, A., Mesquita,C. Dobby, H., Blackadder, L. 2016. Fish and shellfish stocks 2016 Edition. Scottish Shellfish Stocks Section. Marine Scotland Science, 53 pp.

Hinchliff, L, Dick, J Sigwart, J, Gilmore, L. 2015. The velvet swimming crab ( Necora puber) fishery in Northern Ireland : a study of populations and welfare to enhance sustainability Seafish Report SR688. Available at: http://www.seafish.org/media/publications/Velvet_crab_NI_final_report_final__7.10.15_2.pdf

Mesquita, C., Dobby, H. McLay, A. 2016. Crab and Lobster Fisheries in Scotland: Results of Stock Assessments 2009 2012. Scottish Marine and Freshwater Science Vol 7 No 9. 76pp.

Adey, J. M., I. P. Smith, R. J. A. Atkinson, I. D. Tuck and A. C. Taylor 2008. Ghost fishinga of target and non-target species by Norway lobster Nephrops norvegicus creels. Marine Ecology Progress Series 366: 119-127.

Pierpoint, C. (2000) Bycatch of marine turtles in UK and Irish waters. JNCC Report No 310. 32 pp.

Northridge, S., A. Cargill, A. Coram, L. Mandleberg, S. Calderan and B. Reid (2010). Entanglement of minke whales in Scottish waters; an investigation into occurrence, causes and mitigation. Scotland, Final Report to Scottish Government CR/2007/49: 58.

Coleman, R. A., Hoskin, M. G., Von Carlshausen, E., & Davis, C. M. (2013). Using a no-take zone to assess the impacts of fishing: Sessile epifauna appear insensitive to environmental disturbances from commercial potting. Journal of Experimental Marine Biology and Ecology, 440, 100-107.

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

Fahy, E., Carroll, J., Smith, A., Murphy, S. and Clarke, S. 2008. Irelandas velvet crab (Necora puber (L.)) pot fishery, Biology and Environment: Proceedings of the Royal Irish Academy, 108:3,157-175