Last updated on 4 October 2017
Marine Scotland Science (MSS), the scientific division of Marine Scotland, is the entity responsible for conducting the assessment of great Atlantic scallop in Scotland. The latest assessment was conducted in 2011, using data collected up to and including 2010, and an age-structured Time Series Analysis (TSA) was used for the first time (Dobby et al. 2012). Historical trends estimated by the TSA approach show good agreement with MSS’ previous stock assessments carried out using a quarterly Virtual Population Analysis (VPA) (Howell et al. 2003) although the absolute levels of biomass, recruitment and fishing mortality estimated are not directly comparable with previous estimates as different procedures were used to derive these metrics. TSA is considered to be an improvement on the methods previously used; it provides more robust estimates of stock status as it makes use of multiple data sources (landings, catch-at-age, biological data, surveys data) and can cope with the omission of poor quality or missing data. In addition, the estimates of abundance and fishing mortality are calculated with confidence intervals. An update of the 2010 TSA stock assessment is being conducted in 2017 with landings data up to 2015 and surveys data up to 2016 and results will be available soon.
In terms of quality fo the data used for assessment, the accuracy of reported landings data in recent years is supposed to have improved due to the obligations of fishers to report landings by ICES rectangle and, since 2006, at the point of first sale too. Age composition data sampling effort was at its maximum the years previous to the assessment although the lack of consistency in sampling throughout the year (i.e. some quarters not sampled) may also cause bias and/or noise in the annual catch-at-age data (Dobby et al. 2012).
The assessment tends to overestimate SSB in the final year. The addition of data from 2009 and 2010 resulted in a significant downwards revision to the SSB estimates from around 2000 onwards, coupled with downward revision to recruitment and an upwards revision to the estimates of mean fishing mortality. Further exploration of the estimated parameters reveals that the estimated survey catchabilities show a substantial upwards revision (although the trend is still downwards) with the addition of the 2009 survey data. This results in the recruitment being revised downwards and the mean F being revised upwards. Retrospective patterns since 2009 are less apparent.
Last updated on 4 October 2017
Scientific advice is provided by Marine Scotland Science, which is a Division of Marine Scotland, the managing entity. There are no catch limits or reference points in place for the NW Scotland assessment unit. MSS management advice is therefore currently provided on the basis of estimates of recent fishing mortality, recruitment and biomass in relation to historical values. Last advised by MSS was provided in 2012 (Dobby et al. 2012). Recruitment, SSB and catch had all declined markedly over the decade before last assessment so measures to increase spawning stock biomass were advised. However given the apparent temporal autocorrelation in recruitment (i.e. successive recruitments are correlated), it was considered unlikely that SSB would increase quickly even at the relatively low fishing mortality in the last years considered for assessment. An increase in the minimum landing size was proposed as a possible management measure for Scottish scallop fisheries. The survival of discarded scallops is high and therefore most undersized scallops returned to the sea have the potential to grow. This measure therefore has the potential to increase the reproductive capacity of the stock, provided that there is no associated increase in fishing effort. Management measures to control fishing mortality should be considered and could include effort restrictions, spatial and temporal closures or limits on the quantity landed (Dobby et al. 2012).
An independent assessment of the Scottish Scallop fishery, commissioned by the Scottish Government to Poseidon Aquatic Resources Ltd (Cappel et al. 2013), also recommended that effort should be capped and unused scallop licenses to be removed; that minimum landing size be increased to 105mm or 110 mm; and that the dredge and dive fishery management regimes be joined up (amongst other things less directly related to stocks).
There are currently no agreed biomass or fishing mortality reference points for Scottish scallop assessment units. Management considerations are therefore provided on the basis of a comparison of estimates of current fishing mortality, recruitment and biomass in relation to historical values. There are clearly a number of options to be explored for the calculation of reference points for Scottish scallop assessment units (Dobby et al. 2012). The calculation of fishing mortality reference points based on per recruit curves would be relatively straightforward given that the required inputs for the calculations are a direct output from the TSA assessment. In addition, there is a relatively long time series of abundance estimates (either the TSA output or from the surveys) that could potentially be used to derive biomass reference points. It is anticipated that potential reference points will be investigated ahead of MSS’ next round of assessments that is being carried out in 2017.
The most up-to-date stock assessment information provided by MSS for king scallop in Scottish assessment areas (based on ICES statistical rectangles), includes data up to 2010 (Dobby et al. 2012). The estimated values of SSB (total over ages 3-10+) and F averaged over ages 4-6 in the 2011 assessment were 2689 t (muscle weight) and 0.111 yr-1 respectively. The latest recruitment index available (2010) is close to the long-term minimum after 10 yr of decrease. In the early part of the time series (1980-1990), catches were dominated by individuals in the 10+ age category, whereas more recently (after 2000), the catches consist largely of four, five and six year old individuals. Since 2006, there has been a noticeable lack of three year olds in the catch suggesting poor recruitment (Dobby et al. 2012).
Landings (totals and sampled age-composition) are assumed to be representative of catches and no discard sampling takes place. There is evidence that scallop dredging can have a range of effects on discarded juvenile scallops, and on both juvenile and adult scallops that have encountered dredges without being captured. The growth and survival of juvenile scallops in heavily fished areas is reduced compared to those in areas protected from fishing (Beukers-Stewart et al. 2005). The reproductive capacity of scallops on fishing grounds may also be reduced compared to equivalent sized individuals in protected areas which in turn will decrease future yields and profit (Beukers-Stewart and Beukers-Stewart 2009). Fatal damage to captured and non-captured undersize great scallops can vary from 2 % to more than 20 % (Beukers-Stewart and Beukers-Stewart 2009).
The trends described below are based on the available historical data which includes recruitment, SSB and F information up to 2010 (Dobby et al. 2012), and catches up to 2015 which are available here.
Following a period of high recruitment in the late 1990s and early 2000s, recruitment declined and was below the long term average since 2006 and up to 2010 (last year included in the assessment). As a result SSB also declined from the very high levels of early 2000s. Catches were low in the years preceeding the last assessment ( 2005-2010) which is reflected by the low fishing mortality in that period. Catches reached the minimum value of the series in 2011 and increased in the last years to values close to the long-term average.
The management of scallop fisheries in Scotland is the responsibility of Marine Scotland, who have jurisdiction over all territorial waters for Scotland. They have created six Inshore Fishing Groups (IFGs) that help define management measures for each area of coast. IFGs are tasked with developing measures that meet the need for more localized management around the Scottish coast through a system that puts fishermen at the heart of the decision-making process (Scottish Executive, 2005).
Scottish scallop fisheries are not subject to EU or national TAC regulations. The number of scallop licenses in the UK was capped for vessels greater than 10 m in 1999 although this had little effect in limiting fishing effort as far more licences were granted than there were boats participating in the fishery (Brand 2006). The last order regulating scallop fishing in Scotland (The Regulation of Scallop Fishing (Scotland) Order 2017) that came into force in June 2017 establishes the measures for the conservation of king scallops in Scotland. In this order the minimum landing size (MLS) increases from 100mm to 105 mm in most areas of Scotland including the NW Scotland management unit, in agreement with scientific advice provided in 2011 by Marine Scotland Science. The Order specifies dredge number restrictions so that in the part of the Scottish zone beyond the 12 nm, there is a limit of 14 scallop dredges per side of the fishing boat. Inside 12 nautical miles, the following restrictions apply: 1) the total length of any tow bar deployed cannot exceed 7.5m, 2) no more than two tow bars can be deployed at any time and 3) no more than eight scallop dredges per side (i.e. no more than 16 in total). These restrictions will also apply to vessels that wish to fish both inside and outside 12 nautical miles during the same trip. In addition fishing with 10 dredges per side in the 6 to 12 nautical miles zone will be permitted only if a vessel has installed remote electronic monitoring (REM) equipment. This equipment will have to be purchased and installed at the vessel owner’s expense. It will be used by Marine Scotland to monitor the number of dredges being used in the different fishing zones within Scottish waters.
The Registration of Buyers and Sellers of first sale fish and the designation of auction sites, was introduced into national legislation in Scotland in 2005. It was introduced to improve the monitoring and control of landings of fish, and to ensure that landings are properly recorded and verified, including scallop landings
The Common Fisheries Policy (EU) affects the scallop fishery in the NW Scotland assessment unit. Under the Western Waters effort regime (which applies to all UK waters except the North Sea) effort limits are applicable to all vessels over 15 m (including those fishing for scallops). The limits for UK vessels are 1,974,425 KW days for Sub-areas 5 and 6 (which includes the NW Scotlant assessment unit) and 3,315,619 KW days for Sub-area 7.
Most bycatch mitigation measures are currently confined technical measures such as increasing the gap between dredge teeth and the ring-size of the dredge-belly. Modifying dredge-belly ring-sizes to up to and over 85mm can reduce mortality, but the materials used when making these large and more selective ring-sizes are not durable enough to be economically viable at present, so are unlikely to be adopted by the fleet. More work is needed on trialling different belly-ring materials at these larger sizes in order to develop more selective and commercially viable alternatives to those currently in use.
No recovery plan is currently in place. Scottish scallop fisheries are not subject to EU or national TAC regulations, but there is a minimum landing size of 105 mm (The Regulation of Scallop Fishing (Scotland) Order 2017).
Fishers are required to provide information about quantities landed and fishing location by ICES rectangle on either EU logbooks or Shell 1 forms (under 10 m vessels). The implementation of the Registration of buyers and sellers legislation in 2005 requires details of the landed catch also to be recorded at the point of first sale and sales notes are cross checked against vessels landings declarations. This procedure is thought to have improved the accuracy of reported landings data in recent years.
A general lack of compliance with the existing and poorly enforced regulations has been recognized by stakeholders (Cappel et al. 2013). There is no specific information publicly available on the degree of compliance with the MLS (100mm up to May 2017, 105mm from June 2017), but in NW Scoltand, only 2% of the landings in 2010/2011 were smaller than 105 mm suggesting a very high degree of the MLS in the fishery (Cappel et al. 2013).
For the purposes of The Regulation of Scallop Fishing (Scotland) Order 2017 Brittish sea-fishery officers have the powers for enforcement with a fine not exceeding £50,000 on summary conviction and a fine on conviction on indictment.
Scottish Natural Heritage, the Joint Nature Conservation Committee and Marine Scotland developed a priority list of marine habitats and species in Scotland's seas, known as Priority Marine Features (PMFs) which was adopted by the Cabinet Secretary on 24th July 2014 The list contains 81 habitats and species considered to be of conservation importance in Scotland's seas which should be protected from all damaging uses of the marine environment (including fishing).
As a member of the OSPAR convention, Scotland is also required to take actions to protect the OSPAR threatened and declining species and habitats. Currently, as a member of the EU, Scotland also has obligations to protect the species listed in Annex II of the Habitats Directive as well as to conserve “all wild species of bird”, in particular, those listed on Annex I of the Birds Directive.
Whilst there are significant overlaps between these lists, there are some species only covered in one specifically. Here we will prioritise the Scottish Government’s PMF list but cover also OSPAR’s list of Threatened and Declining species. Many of the ‘features’ included on these lists as ‘habitats’ could easily also be considered ‘species’, for example seagrass beds or horse mussel reefs. These are highly vulnerable to dredging but will be considered below under ‘Habitats’ – where they are highlighted in bold.
Research has been undertaken to understand which PMF species are vulnerable to dredging and this has been presented in the FEAST tool. This tool defines the following species as high and medium risk to dredge damage.
- High: Blue ling, ocean quahog (aggregations)*, orange roughy*, sandeels, native oyster beds*, fan mussel aggregations.
- Medium: black guillemot, common skate*, kelp and seaweed communities on sublittoral sediments
Those species which are starred are included on the OSPAR threatened and declining species list too. Whilst the FEAST assessment did not extend to OSPAR species, OSPAR’s own assessments define threats faced by each species and make recommendations for management which add further justification for these categorisations.
Some work has been underway to protect these species from dredging through a network of marine protected areas that include: 30 nature conservation MPAs under the Marine (Scotland) Act 2010 or the Marine and Coastal Access Act 2009; 48 Special Areas of Conservation (SACs) under the EU Habitats Directive.
King scallop is the only target species of this fishery but some commercially important bycatch species can be retained for sale (e.g. edible crab, cuttlefish, monkfish). Damaged king scallops are the most significant bycatch (Beukers-Stewart and Beukers-Stewart 2009). Other bycatch species include: fish (flatfish, dogfish, skates, rays, monkfish and dragonets), crustaceans (edible crabs, swimmer crabs, spider crabs and hermit crabs), urchins, molluscs (bivalves and gastropods), starfish, brittlestars and cephalopods (octopus and cuttlefish) (Howarth and Stewart 2014). Most bycatch is discarded damaged, dying or dead. The most sensitive species to dredge damage include the seven armed starfish, Luidia ciliaris, the edible sea urchin, and the commercially important edible crab (Howarth and Stewart 2014).
There are no specific studies carried for this assessment unit but a study off the Isle of Man found that for every scallop captured by a Newhaven dredge (the most used type of dredge in Scotland), four individuals of bycatch were also caught (Hinz et al. 2012). Another study in the Irish Sea recorded that 97.6% of tows of scallop gear generated fish by-catch belonging to 50 different species, of which the majority were monkfish (Craven et al. 2013). The bycatch of edible crab is specially concerning since scallop dredging captures approximately 25% of the edible crabs present in the path of dredges whereas more than 40% of the remainder may be left dead or dying on the seabed, wasting a resource that otherwise would be available to other fishing gears (Howarth and Stewart 2014). There is also evidence that bycatch in the Isle of Man scallop dredge fleet was at least partially responsible for a decline in monkfish over a 14 year period (Craven et al. 2013), a species subject to EU TAC regulations but without accepted reference points in Scotland. Mitigation of bycatch by vessels scallop dredging is currently done through the spatial and temporal restrictions that are in place (explained in the Marine Reserves section), rather than gear adjustments.
Scallop dredges are considered to be among the most damaging of all fishing gears to benthic communities and habitats (Howarth and Stewart 2014). Biogenic substrates and their associated benthic communities are the most sensitive to disturbance by scallop fisheries. Specific studies on maerl beds suggest that dredging can led to a 70-80% reduction in live maerl, potentially impacting commercial fisheries by diminishing nursery-area function (Howarth and Stewart 2014). Modioulus reefs have been identified as particularly vulnerable to dredging and experimental studies showed that experimentally scallop dredging Modiolus reefs off the Isle of Man and Wales reduced the biodiversity of the associated community by 59-90% (Cook et al. 2013). On the other end benthic communities in gravel and mixed sand and mud substrates will recover if protected from fishing, although time frames vary for different species (Beukers-Stewart and Beukers-Stewart 2009).
Habitats are protected in Scotland as part of national legislation within the list of PMFs, as part of OSPAR and, currently, within the EU Habitats directive (Annex 2). The FEAST tool indicates the following habitats have a high and medium vulnerability to scallop dredging.
- High: Burrowed mud, Carbonate mound communities, Continental shelf coarse sediments, Continental shelf mixed sediments, Continental shelf sands, Coral gardens*, Deep sea sponge aggregations*, Deep sea mixed sediments, Deep sea muddy sands, Deep sea muds, Deep sea sands, Inshore deep mud with burrowing heart urchins, Low or variable salinity habitats, Seamount communities, Seagrass beds*, Tide swept coarse sands with burrowing bivalves, Flameshell beds, Horse mussel beds*, Maerl beds*, Maerl or coarse sand with burrowing sea cucumbers, Northern sea fan and sponge communities
- Medium: Continental shelf muds
Starred species are also included on the OSPAR threatened and declining species list, those highlighted in bold may also be considered as ‘species’ by some research. Because they are ‘habitat forming species’, we consider them habitats to conform with OSPAR.
Again, some progress towards managing the impact of scallop dredging on these habitats has been made through the designation of MPAs. However, the protection offered by these sites is somewhat piecemeal and many of these MPAs remain open to dredging. Of the 41 MPAs and Special Areas of Conservation (SACs) designated in Scotland’s inshore seas (including but not limited to NW Scotland), only 10 sites are currently fully protected from dredging, and 15 of these sites have no protection at all.
In line with some recently established policies and initiatives, closing areas to some or all types of fishing is likely to increase in the UK over the next few decades. The EU Marine Strategy Frameworks Directive (MSFD), Birds and Habitats Directives and OSPAR have all initiated the process of establishing a coherent network of MPAs within European waters (Howarth and Stewart 2014). On a national level, the ongoing implementation of Scottish MPAs has lead to the creation of a network of MPAs intending to achieve a variety of management goals; principally to conserve biodiversity and promote the sustainability of fisheries. The Scottish MPA network covers approximately 20% of our seas and include, among others:
In the areas where this fishery operates there are five inshore MPAs: Lochs Duich, Long and Alsh, Monach Isles, Wester Ross, Small Isles and Loch Sunart. Dredging is prohibited year round in three of them which are also considered SACs: Wester Ross, Loch Sunart and Lochs Duich, Long and Alsh. Dredging is also prohibited in three additional SACs in NW Scotland: East Mingulay, Loch Laxford and St Kilda.
Map of all Scottish nature conservation Marine Protected Areas: