Crab, Velvet

Necora puber

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

All areas


Picture of Crab, Velvet

Sustainability rating four info

Sustainability overview

Velvet crabs were traditionally caught as bycatch and were deemed as a pest species in Northern Ireland, and subsequently discarded. They were a popular species in 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. The French market served as an alternative market until 1984, but declines in these regions resulted in a commercial development in UK and Irish spider crab fisheries, where the Northern Irish fishery, has been emerging as a valuable velvet swimming crab fishery to these international markets but there is concern over declines in their landings in recent years. 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.

The velvet crab fishery is generally taken in the pot fishery as bycatch, while targeting brown crab (Cancer pagurus). However, in the Irish Sea, there are reduced levels of brown crabs, and the velvet crab fishery is relatively more popular.

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: 1 info

Stock Area

Northern Ireland

Stock information

The stock status of velvet crabs is unknown, however, there is concern over declines in the velvet crab landings in Northern Ireland over recent years.

There are significant data gaps regarding population levels, sex ratios and reproductive behaviours of velvet crabs in Northern Irish waters. Previous reports have suggested that further research is required in the fishery.

Management

Criterion score: 0.75 info

There are insufficient measures to protect the velvet crab fishery in Northern Ireland. Management includes a Minimum Conservation Reference Size (MCRS) of 65mm, a bycatch limit of crab claws per day, licence requirements, a requirement to record catches on sales notes and Monthly Shellfish returns, Vessel Monitoring Systems for vessels over 12 metres in length.

The industry have proposed an increase to the MCRS and a buy-back scheme. The buy-back scheme would mean that crabs which are at a size between the current legal MCRS and the proposed higher voluntary MCRS, would be marked to ensure that, when caught, they can be quickly identified and discarded, so that they are not landed. This is particularly important for velvet crabs at this size, because when they are retained on-board and discarded at a later point, they are unlikely to survive. Even when fishers adopt measures to increase their chance of survival - such as covering on-board boxes of velvet crabs with damp seaweed they are insufficient to limit their mortality before being discarded. Therefore, it is better practice to limit their mortality by discarding them upon capture, ensuring they are handled gently and for a limited time. Since many females are berried in the Spring, increased management could be implemented to protect the broodstock during this time.

As part of the Northern Ireland Marine Act 2013, there are studies ongoing to map and manage habitats, which considers the velvet crabas vulnerability to fishing.

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. 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.

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). Ghost fishing in creel fisheries, is also considered to be low.

References

Cappell, R., C. Bannister, F. Nimmo 2011. Northern Ireland Brown Crab Strategya

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

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 http://www.seafish.org/media/publications/Velvet_crab_NI_final_report_final__7.10.15_2.pdf

Howard, A. E. (1982). The distribution and behaviour of ovigerous edible crabs Cancer pagurus and consequent sampling bias, ICES Journal of Marine Science, 40:3, 259-261

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

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. 2007. Aspects of the sustainability of creel fishing for Norway lobster, Nephrops norvegicus (L.), on the west coast of Scotland. Presented in candidature for the Degree of Doctor of Philosphy.

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