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

Shetland


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.

Crab and velvets are mainly sold live to export markets with full documentation from point of sale/landing.

A stock assessment has shown that fishing mortality is high and this has resulted in the Marine Stewardship Councilas certification being suspended for the velvet crab fishery.

Management has been implemented to reduce the pressure on the velvet crab stock, however, management has been slow to react as three of the four fishing mortality indicators are below the target reference point.

Creels generally present a low risk to the habitat and bycatch.

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 data on biomass trends. Fishing mortality estimates were much higher in Shetland compared to other areas in Scotland, however, there is no conclusive fishing mortality estimate due to inconsistencies in biological parameters.

Fishing mortality trends were estimated from four stock indices, which generally showed a negative status: 1. Landings per unit effort (LPUE); 2. The mean size of males in the catch (including sub-legal crabs); 3. the sex ratio and 4. the level of fishing effort. Both LPUE and mean size of males were below the TRP but above the LRP in 2016. The sex ratio stock indicator was below the LRP. The level of fishing effort was around the TRP.

There is a relatively high proportions of gravid females, however, there has been a small decrease in the size of males over the last ten years. Available data shows that it is highly unlikely that recruitment is impaired. Both a reduced level of catch-per-unit-effort and overall decrease in crab size may have a negative impact on landings.

Management

Criterion score: 0.75 info

There is a suite of management measures to protect the stock and there is precautionary management available if the stock declines. However, management measures have not restrict fishing mortality to appropriate levels. Marine Scotland has implemented velvet crab closures in August 2018 for all Shetland Shellfish Management Organisation (SSMO) licence holders, to improve the velvet crab stocks.

The SSMO Management Plan covers the velvet crab fishery within 6nm around Shetland. The SSMO implemented new Harvest Control Rules (HCRs) in January 2017 as it calculated new reference points. Management measures include a limited entry licensing policy, a limit of 600 creels (only 240 of which may target velvets), escape gaps, a closed season for a minimum period of 8 consecutive weeks between June and October (depending on location to reflect moult period), a minimum landing size (MLS) of 70mm (significantly above the size at maturity) and a ban on use of crab as bait.

The level of management increases if or when the velvet crab stock appears to decline. In this case, increased management may include ceasing all new licences or vessels, increases in Minimum Conservation Reference Size (MCRS), closures or a complete fishery closure. However, these measures appear to be implemented at a very late stage.

Monitoring
Regular monitoring in the fishery collects data on the stockas size structure, sex ratio, the percentage berried, patterns of moulting, biological parameters (i.e. length-weight relationships) and discard mortality.

Surveillance and enforcement
Creels must be tagged to aid enforcement.

Capture Information

Criterion score: 0 info

Bycatch
The main retained species in the Shetland creel fishery are brown crab, velvet crab, lobster and green crab. The main bycatch is the great spider crab (Hyas araneus). Though their stock status is unknown, it is highly likely to be within biologically based limits and can be released alive. A potential endangered, threatened and protected (ETP) species is the minke whale: one entanglement incident was recorded in the last 5 years but Shetland is markedly lower risk than elsewhere (such as the Sea of the Hebrides region, the Little Minch and east coast of Scotland off Angus). The SSMO has produced a SSMO Cetacean Entanglement Prevention Guidea to reduce this risk and records incidents.

Habitat
Creels and pots pose a lesser impact on habitat than mobile fishing gear but can present localised impacts.

Velvet crabs are not considered to be keystone species in the ecosystem.

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

SSMO. 2018. Velvet Crab Closures. Available at: https://www.ssmo.co.uk/about/velvet-crab-closures. [Accessed om 11/09/ 2018].

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