Edible crab

Assessments are conducted by Marine Scotland Science on triennial basis and the most recent assessment considered data from 2009-2012 (Barreto and Bailey, 2014). No effort data from the fishery is available.

Regional assessments of crab stocks around Scotland are based on size compositions from commercial catches and biological parameters are used to estimate fishing mortality for males and females separately via Length Cohort Analysis (LCA), in the absence of other data (Jones et al., 2010; Mesquita et al., 2011). Short-term trends in the stock are not identified by LCA and although growth overfishing can be detected by changes in length composition, recruitment overfishing (depletion of spawners) cannot be diagnosed (ICES, 2011). The assessment is very sensitive to changes in the biological parameters used. An exploratory analysis of mean size trends was conducted for the first time in 2011, aiming to add information on recruitment and fishing mortality (Mesquita et al., 2011).

There are some concerns about the state of crab stocks, namely on whether the inshore and offshore are linked or part of the same population, and how fishing in one area may affect the stock. Tagging study to obtain information on migratory and life history patterns of brown crab to the north west of Scotland provided evidence of significant movements of crab stocks, in particular movements of female crab from offshore to inshore areas (Jones et al., 2010). However, more tagging studies are needed to access the linkage between inshore and offshore stocks in other areas.

No specific management actions have been advised, but overfishing on both males and females was noted in the 2009-2012 assessment. Higher yield and biomass per recruit in the long term could potentially be obtained by reducing the level of fishing mortality (effort) (Barreto and Bailey, 2014).

Last updated on 08 Dec 2014

Stock status is assessed in evaluated in terms of F_MAX, the fishing mortality that maximizes yield per recruit and defines growth overfishing. F_MAX is used as a proxy for F_MSY. All F_MSY proxy values remain preliminary and may be modified following further data exploration and analysis (Barreto and Bailey, 2014). F_MAX for females was estimated at 0.29 and for males at 0.36.F_0.1 is also determined (Mesquita et al., 2011).

Fishing mortality was estimated to be above recommended levels (F_MSY) for both males and females in East Coast (Barreto and Bailey, 2014). Landings have been increasing since 2009.

Males compose around 60% of landings. The exploratory trend analysis conducted for the first time indicated a decrease in size of larger crabs on the East Coast when compared to the early 1990s, but an increase when compared to earlier sizes, interpretable as either a recent increase in fishing mortality or as due to a change in fishing or discard practices (Mesquita et al., 2011).

Last updated on 07 Dec 2014

The mean 2006-2008 fishing mortality for female stocks (0.33) was close to F_MAX (0.29) while males (0.54) are being fished above F_MAX (0.36). Recruitment overfishing cannot be estimated (Mesquita et al., 2011).

Crab landings in Scotland have increased over the past 30 years as improved technology led to a larger offshore target fleet, and new markets have developed as live crab become transportable. Landings from the East Coast have been variable over the years but no overall trend is detectable (Mesquita et al., 2011).

High recruitment is thought to have occurred in 2003 and 2005, from market sampling data (Mesquita et al., 2011).

An EU-regulated minimum landing size of 130 or 140 mm, by area, is the principal management measure. Additionally, there are EU measures in place to restrict the fishing effort (kW days) of all vessels > 15 m (including creel boats) in ICES Subarea VI (Barreto and Bailey, 2014). A shellfish license is required and the only catch limit in place is 25 crabs/day for non-license holders (Mesquita et al., 2011). The retention of detached crab claws is also limited (EU, 1998).

Last updated on 05 Sep 2012

None in place.

Under-reporting of landings is thought to have been an issue in the past, but not since the 2005 introduction of buyers and sellers regulations (Mesquita et al., 2011).

There are reports of otter, a protected species in Scotland, bycatch in creel fisheries (Marine Scotland, 2008) although impacts are estimated to be low (Hervás et al., 2012). Sea turtle and marine mammal entanglement in pot ropes is also an issue (Hervás et al., 2012); leatherback turtles are globally critically endangered (Sarti Martinez, 2008) and bycatch rates in fisheries may be threatening their survival (Marine Scotland, 2008). Bycatch rates of right whales (IUCN Endangered; Reilly et al., 2008a), humpback whales (IUCN Least Concern; Reilly et al., 2008b) or minke whales (IUCN Least Concern; Reilly et al., 2008c) are not quantified (Hervás et al., 2012).

Scottish creel (pot) fisheries are mixed, also landing velvet swimcrab Necora puber and European lobster Homarus gammarus. Velvet crabs on the East Coast are being fished at F_MAX but lobsters above this level (Mesquita et al., 2011). Red crab Chaceon quinquedens, stone king crab Lithodes maja and green crab Carcinus maenas make up a minority of landings. Common spiny lobster Palinurus elephas and Norway lobster Nephrops norvegicus may also be landed (Mill et al., 2011), but the state of the latter’s stock in the region is unknown (ICES, 2012). In addition to cod, undifferentiated ‘Rockling’ and ‘wrasse’ have been reported among finfish bycatch, as have ling, conger eel, dogfish, poor cod, pollack, saithe and haddock (Smith et al., 2010). Non-target species are usually released alive. Discards in crab fisheries are sampled only on an irregular basis (ICES, 2013)

Habitat impacts due to the gear type used are negligible, but ghost fishing due to lost gear is possible.

Last updated on 05 Sep 2012

No closed areas are defined for the fishery on the East Coast. Special Protection Areas (SPAs) under the Birds Directive and Special Areas of Conservation (SACs) with marine components are defined on the East Coast and several potential MPA locations are being assessed off the East Coast related to habitat feature, sandeel and horse mussels (Marine Scotland, 2012).