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Velvet crab, Scottish Waters, Creel Fishery

fish

Necora puber

Content last updated
15th Feb 2017

Stock:
Velvet crab in Scottish waters

Management:
Marine Scotland Science

Overview

Velvet swimming crab, Necora puber, are found all around the British and Irish coastline, as well as further south in the Mediterranean and Northern Africa (Shelmerdine & White, 2011).  They are a fast moving crab that in the past were regarded as a pest species by fishermen.  However, after a collapse of the Spanish and Portuguese fishery fishermen on the west coast of Scotland and then in Orkney and Shetland began catching velvet swimming crab commercially to take advantage of the gap in the market.  They tend to be most commonly found at shallow depths close to shore on rocky tidal substrate (Tallack, 2002).

Velvet crabs are sexually dimorphic in size as females grow to smaller sizes than males. Size at maturity is thought to be 44mm in females and 53 mm in males (Hearn, 2004).  Males and females moult at different times of the year; the main moult for males is between April and July whereas females moult between May and August. Mating occurs after females have moulted, when the shell is still soft. Fecundity estimates, from a study that took place on the Shetland fishery, found that female crabs with carapace width ranging from 56mm – 96mm had broods containing approximately 160,000 to 200,000 eggs. It is thought that this species of crab does not perform extensive migrations and their movements are usually restricted to a few hundred metres (Baretto and Baily, 2016). The Scottish velvet crab fishing grounds are divided into 12 areas for assessment purposes (Fig. 1) (McLay et al, 2016).

VC_distribution

Figure. 1 reel fishery assessment areas and Scottish velvet crab landings (tonnes) in 2014 (From: McLay et al, 2016).

 

References

Hearn, A. 2004. Reproductive biology of the velvet swimming crab, Necora puber (Brachyura: Portunidae), in the Orkney Islands, UK.        Sarsia North Atlantic Marine Science (89):1-9.

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

Shelmerdine, R.L. & White, E. (2011) Escape gaps for velvet crabs (Necora puber); stock and economic benefits for the catching sector. NAFC report for Scottish Industry Science Partnership (SISP).

Tallack, S. (2002). The biology and exploitation of three species in the Shetland Islands, Scotland: Cancer pagurus, Necora puber and Carcinus maenas. PhD Thesis. NAFC/UHI.

Stock Status

less risk

more risk

Velvet crab in Scottish waters, has been scored a very high risk. This is because fishing mortality has been above Fmsy in recent years in most assessment areas, no precautionary limits have been defined and there are no reliable indicators or proxies of abundance in most assessment areas.

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Management

less risk

more risk

Velvet crab in Scottish waters, has been scored a very high. This is because data is limited in several of the assessment areas to develop any management measures and there is no control (expect in Shetland) of fishing effort with only minimum landing size that changes depending on landing area.

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Bycatch

less risk

more risk

The bycatch risk of this fishery has been scored as low risk. This is because whilst discarding of undersized and unwanted crabs and lobster occurs, these are released alive on hauling and survival rates are believed to be high.  Catch of protected, endangered and threatened species is minimal.  “Ghost fishing” by lost pots is not considered to be a problem.

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Habitat

less risk

more risk

The habitat risk of this fishery has been scored as low risk. This is because although the gear touches the seafloor it is unlikely to have a significant effect on habitats.

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Outlook

Type Current Risk Status Outlook Reason

Stock

Very high Stable

The status of the stock is likely to remain in high risk as there is no information on biomass and no controls over the amount that can be caught.

Management

Very high Stable

Estimates on fishing mortality are not translated into advice for management.

Bycatch

Low Stable

Measures to improve selectivity are available but the extent of their use is not known and not likely to be mandatory due to high survivability of discards in the creel fishery.

Habitat

Low Improving

Technical and spatial management measures are under development and will likely reduce the risk further.

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