Velvet crab, Scottish Waters, Creel Fishery

Transcription

1 Velvet crab, Scottish Waters, Creel Fishery Content last updated 19th Jun 2018 Stock: Velvet crab in Scottish waters Management: Marine Scotland Science Velvet crab, Scottish Waters, Creel Fishery 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). Figure. 1 reel fishery assessment areas and Scottish velvet crab landings (tonnes) in 2014 (From: McLay et al, 2016). Hearn, A Reproductive biology of the velvet swimming crab, Necora puber (Brachyura: Portunidae), in the Orkney Islands, UK. Science (89):1-9. Sarsia North Atlantic Marine Mclay, A., Mesquita,C. Dobby, H., Blackadder, L 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. 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 required to develop any management measures, and there is no control of fishing effort. 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 high. Catch of protected, endangered and threatened species is minimal. Ghost fishing by lost pots is not considered to be a problem.

2 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. Outlook Type Current Risk Status Outlook Reason Stock Very high Deteriorating The status of the stock is likely to remain in high risk and recent evidence suggest an increase in areas fished above a sustainable threshold. 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.

3 Stock Status Details less risk more risk Time-trends In recent years, total annual landings of velvet crabs in Scotland have decreased to about 1500 tonnes from 2800 in 2007.The three areas that have historically had significant velvet crab fisheries are the Hebrides, Orkney and South Minch, although the two latter have shown a slight decrease in landings over the last years (Figure 1). These three areas accounted for over 65% of velvet crab landings in Scotland in the period Most landings are taken from inshore areas and only very small amounts were recorded from offshore grounds in Papa and Sule (Figure 1) (Mesquita et. al 2017). Landings data are collated by Marine Scotland from sales notes and EU logbook and Fish1 forms. Marine Scotland Science also conducts a market sampling programme which registers carapace width and sex. Assessments for the period were conducted for the Clyde, Hebrides, Orkney, South Minch, East Coast and South East. These assessments showed that most velvet crab areas in Scotland continue to be fished close to or above the Fishing mortality Maximum Sustainable Yield (Fmsy) proxy (Fig. 2a and b; Mesquita et. al 2017). In the Hebrides, recent fishing mortality was estimated for males to be below F MSY however females were fished above F MSY. Similarly, in the South East, males were fished at F MSY while females were fished above F MSY. In the South Minch, both females and males are now being fished above Fmsy (Fig. 2). The Shetland Shellfish Management Organisation (SSMO) conducts additional assessments using reference points to inform management (see Seafish assessment for Velvet swimming crab in Shetland inshore waters for further details). Fig. 1. Velvet crab landings (tonnes) into Scotland by assessment area, Taken from Mesquita et al, Fig. 2. Creel fishery assesment areas and estimated fishing mortality in relation to Maximum Sustainable Yield for the period a) , and b) Taken from McLay et al, Stock structure and recruitment The velvet swimming crab population structure around Scotland is poorly understood and many of the stock assessment areas have insufficient sampling data to be assessed by Marine Scotland Science (MSS) (McClay et al., 2016). The current assessment areas are based largely on past fishing patterns. No recruitment data is collected in Scotland and there is not much information on the dispersal and settlement of velvet swimming crab juveniles. Nevertheless, there is evidence that when in the plankton stage they show habitat preferences and although they are driven by oceanographic/hydrodynamic processes they are able to use their relatively strong swimming activity to affect their settlement location (Lee, J, 2004). Once settled there is no evidence that velvet crabs undertake extensive migrations (McClay et al., 2016).

4 Data gaps and research priorities Information on population structure of velvet crabs should be undertaken and ideally incorporate studies on population genetics/morphology and larval dispersal. Additionally, many of the stock assessment areas have insufficient sampling data. Information on creel fishing effort is lacking and this precludes the use of a Landings Per Unit of Effort (LPUE) as an indicator of crab abundance (Mesquita et al., 2017). Information on the number of creels used when fishing for crabs could provide a useful measure of effort, and this field has been recently added to the reporting form for vessels under 10 m (FISH1 form) to allow calculation of LPUE in the future. Growth parameters used in stock assessment models for velvet crabs use were estimated from tagging studies more than 40 years ago. Available data suggests very different growth rates among areas, therefore, site specific evaluation of growth parameters via field studies is needed (Mesquita et al., 2017). Lee, J Ecology and behaviour of postlarvae and juveniles of the velvet swimming crab Necora puber (L.). PhD Thesis. University of Plymouth. 154 pp. Mclay, A., Mesquita,C. Dobby, H., Blackadder, L Fish and shellfish stocks 2016 Edition. Scottish Shellfish Stocks Section. Marine Scotland Science, 53 pp. Mesquita, C., Dobby, H. McLay, A Crab and Lobster Fisheries in Scotland: Results of Stock Assessments Scottish Marine and Freshwater Science Vol 8 No pp.

5 Management Details less risk more risk In 2015, total annual landings of velvet crabs in Scotland decreased to about 1500 tonnes from 2800 in 2007 (Mesquita et al., 2017). Stock Harvesting Strategy For animals that moult, age determination is generally not possible, therefore stock assessment are usually based on length. The Length Cohort Analysis (LCA) method uses official landings and length frequency data collected as part of Marine Scotland Science (MSS) market sampling programme. Obtaining this information is sometimes hard as velvet crabs are often landed in remote harbours and quickly dispatched to fishing processors or shipped abroad, making it more difficult to get samples (Mesquita et al., 2016). Estimates of growth and natural mortality are incorporated into the assessment method to estimate fishing mortality. These assessments are performed on a regional basis for males and females separately. Marine Scotland Science aims to run these assessments every three years (Mesquita et al., 2016). Data on length at landings are sometimes insufficient to run stock assessments in all areas. Marine Scotland Science categorises the quality of these data using four different criteria: number of trips/individuals sampled, number of years for which data is available, sampling seasonality, and length frequency distribution shape. Stock assessments are not carried out for areas where one or more criterion is classified as poor. For the period , sampling data were insufficient for 5 out of 12 stock assessment areas: Mallaig, North Coast, Papa, Sule, and Ullapool (Mesquita et al., 2017). Surveillance and Enforcement Vessels fishing for velvet crabs must have a license with a shellfish entitlement, however, there is no limit on the amounts that can be landed. Owners of vessels of length 10 metres and under with an entitlement must complete and submit the FISH1 form on a weekly basis. For vessels over 10 metres in length, fishing activity data must be recorded in an EU logbook and submitted within 48 hours of landing. Vessels without the shellfish entitlement are allowed to land a maximum of 25 crabs per day (Mesquita et al., 2016). The minimum landing size has been recently changed from 65 mm to 70 mm carapace width. Landing of berried females is also prohibited. Mesquita, C., Dobby, H. McLay, A Crab and Lobster Fisheries in Scotland: Results of Stock Assessments Scottish Marine and Freshwater Science Vol 7 No 9. 76pp Mesquita, C., Dobby, H. McLay, A Crab and Lobster Fisheries in Scotland: Results of Stock Assessments Scottish Marine and Freshwater Science Vol 8 No pp.

6 Bycatch Details less risk more risk Targeting and behaviour Velvet crabs are often caught in the inshore creel fishery with lobster and brown crab. Very few fishermen fish solely for velvet crab, although some target the species at certain times of the year (Mesquita et al, 2016). The crab fishery uses static gear known as creels. These creels consist of a metal frame covered in small mesh netting, with mesh eyes that make entering easier than exiting for the crab. They vary in detail by location, including variations in overall shape, entrance height, opening and bait type. The creels are typically baited with fish, often frozen mackerel or horse mackerel or waste from local fish processers. Creels are set in leaders that comprise of between creels on a single line, but usually vessels have between 10 to 25 creels per leader as they are limited by the size of their boat. Creels are normally placed at specific depths and bottom types in locations that the fishermen know to be good spots. Soak time or time that the creels are left on the seafloor before being hauled is generally a few days or less. Catch rates have been shown to vary with longer soaking times as this allows greater opportunity for capture but conversely it also increases the opportunity for escape after the bait has been consumed, and studies with other creel-caught crustacea have shown that the gender and species interactions have a significant impact on capture rates, depending on the sex and size of the first animal to be trapped (Watson and Jury, 2013). Ghost fishing in creels is considered to be low. Most species that are commonly caught in creels (e.g. crabs, starfish, cod) are able to escape the creels after days or weeks (Adey et al. 2008). Inkwell pots and creels have been found to allow most captured individuals to escape after about 3 days. Escapes will eventually occur from parlour traps and soft-eyed traps by crabs gradually cutting their way through the netting, though it might not occur until after about 3 months (Swarbrick and Arkley, 2002). Once the bait is consumed, ghost creels will cease to fish (Adey et al. 2008). Evidence of bycatch risk There are currently no discard data regularly collected for the crab and lobster fisheries in Scotland and any mortality due to discarding practices is not taken into account in the assessments (Mesquita et al, 2016). Anecdotal information and recent ad hoc studies suggest that crab and lobster discard rates in the target creel fisheries are variable and occasionally high (>50% by number) but survival rates are also high. Bigger mesh sizes allow undersized individuals of the target species as well as smaller species of crab to escape in many instances. However, even if they are unable to escape most soft, berried, undersized or otherwise non-targeted individuals are returned alive when creels are hauled and the catch sorted. Occasionally bycatch of other species is also found in creels, fish species such as cod, poor cod and rockling as well as a variety of invertebrates. These are generally discarded alive if the fish are not used for bait (Tallack, 2002). Rare, threatened or iconic species are rarely caught in pot fisheries though leatherback turtles have very occasionally become entangled in pot ropes and occasionally whales have also been found entangled (Pierpoint, 2000). There is also the potential for otters or birds to interact with creels, however the configuration of leaders is thought to significantly decrease the chance of entanglement with such animals, especially in comparison to pot fisheries in North America for example (MSC, 2012). Further studies may be needed as more recent evidence suggests that whale may be more heavily impacted than initially thought. Of about 11 or 12 baleen whales that strand every year in Scotland, half of them appear to have died due to entanglement (Northridge et al. 2010). Mitigation measures Bycatch of undersized crab is regulated by a minimum landing size (MLS). Landing of other stages (soft, or berried) are also prohibited. Minimum landing sizes also apply to other commercial species taken with velvet swimming crabs (e.g. edible crab), however edible and velvet crab grounds are unlikely to be in the same areas. Adey, J. M., I. P. Smith, R. J. A. Atkinson, I. D. Tuck and A. C. Taylor (2008). Ghost fishing of target and non-target species by Norway lobster Nephrops norvegicus creels. Marine Ecology Progress Series 366: Mesquita, C., Dobby, H. McLay, A Crab and Lobster Fisheries in Scotland: Results of Stock Assessments Scottish Marine and Freshwater Science Vol 7 No 9. 76pp. 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. Pierpoint, C. (2000) Bycatch of marine turtles in UK and Irish waters. JNCC Report No pp. Swarbrick, J. and Arkley, K. (2002) The evaluation of ghost fishing preventers for shellfish traps. Seafish Report No SR pp. 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. Watson, W., Jury, S.H., The relationship between American lobster catch, entry rate into traps and density. Mar. Biol. Res. 9 (1),

7 Habitat Details less risk more risk Gear effects, targeting and behaviours Creels are set in leaders that are typically comprised of of the creels. Leaders are then shot over the desired location and settle on the bottom. The seafloor tends to be substrate suited to the particular target species, relatively shallow and usually fairly hard or gravelly bottoms that are often subjected to a degree of disturbance from adverse weather conditions. Evidence of habitat risk Static gear such as creels are known to have notably less impact on benthic habitats than other fishing gear such as bottom trawl or dredge (Bernette, 2001; Polet and Depestele, 2010). There have been a few studies on the impact of pots and traps on the benthos around the UK. A four year study on the no-take zone around Lundy Island off the south west coast of England indicated that there was no difference over the time period between areas fished with pots and those left untouched (Coleman et al., 2013). Short term experimental assessments of creel disturbance suggest that it has minimal effect on sea pen (Pennatulacea) which are species of conservation importance, although these experiments potentially used lower intensity regimes than commercial creeling (Kinnear et al. 1996). It has been shown (Eno et al, 2001) that these species are able to avoid damage by creel gear, as some species are able to withdraw into the substrate as creels approach, or being able to re-establish themselves if up rooted. With some caveats in relation to effects on certain sea pen and brittle star species the physical effects of creeling on these species is considered to be low, and therefore effects on the structured habitat provided by these species is low (Adey 2007). Mitigation measures There is currently a National Marine Planning in process whereby a plan for Scotland s marine areas under the Marine (Scotland) Act and the UK Marine and Coastal Access Act (2009) is being prepared. Many of the habitats and proposed protection areas have been or are being mapped ( and there is an ongoing process which is aimed at coherent management taking into account their vulnerability to fishing. 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. Retrieved from Bernette, M. C. (2001). A review of the fishing gear utilized within the Southeast Region and their potential impacts on essential fish habitat. National Marine Fisheries Service. 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, Eno, N. (2001). Effects of crustacean traps on benthic fauna. ICES Journal of Marine Science, 58(1), doi: /jmsc Kinnear, J. A. M., P. J. Barkel, W. R. Mojeiwicz, C. J. Chapman, A. J. Holbrow, C. Barnes and C. F. Greathead (1996). Effects of Nephrops creels on the environment. Fisheries Research Services Report No. 2/96. Aberdeen, Scottish Office Agriculture, Environment and Fisheries Department: 24. Polet, H., & Depestele, J. (2010). Impact assessment of the effects of a selected range of fishing gears in the North Sea (p. 120). ILVO. All content 2018 Seafish. Origin Way, Europarc, Grimsby, DN37 9TZ. This page created on 23rd July 2018 at 08:15am.