Download Megrim in northern North Sea and West of Scotland

Megrim in northern North Sea and West of Scotland
Megrim in northern North Sea and West of
Scotland
Content last updated
7th Jun 2016
Stock:
Megrim in Divisions IVa and VIa (Northern North Sea and West of
Scotland)
Management:
EC and ICES
Overview
Megrim (Lepidorhombus whiffiagonis & Lepidorhombus boscii) are two species of commercially important demersal flatfish whose range
stretches from the Mediterranean Sea to Iceland. The two species, common megrim L. whiffiagonis and four-spotted megrim L. boscii are
managed as one in the northern shelf stocks, although information available indicates that the proportion of L. boscii is negligible in
Scottish catches(ICES, 2007) and becomes more common in waters further south (Macdonald et al., 2013). Megrim tend to be regarded as
a deep-water fish but can be found at depths ranging from 50-850m but are most common around 100-300m (ICES, 2007; Gerritsen,
2010). Spawning occurs between February and April. Generally and historically megrim was caught on the northern shelf as a bycatch
species of the demersal mixed fishery, however in recent years it has become a more important commercial species and can be targeted
at certain times (Macdonald et al., 2014).
References
Gerritsen, H. D., McGrath, D., Lordan, C., & Harlay, X. (2010). Differences in habitat selection of male and female megrim (Lepidorhombus
whiffiagonis, Walbaum) to the west of Ireland. A result of differences in life-history strategies between the sexes?. Journal of Sea Research,
64(4), 487-493.
ICES (2007) Report on the Working Group on the Assessment of Northern Shelf Demersal Stocks (WGNSDS), Galway, Ireland. ICES
advisory committee on fisheries management. 868 pp.
Macdonald, P., Angus, C. H., & Marshall, C. T. (2013). Spatial variation in life history characteristics of common megrim (Lepidorhombus
whiffiagonis) on the Northern Shelf. Journal of sea research, 75, 62-68.
Macdonald, P. & Crego Prieto, V. (2013). Assessment of the population structure of common megrim (Lepidorhombus whiffiagonis) on the
Northern Shelf using genetic markers. NAFC Marine Centre report, 31p.
Stock Status
less risk
more risk
The megrim stock in the northern North Sea and west of Scotland waters has been scored as very low risk. This is because fishing
mortality is well below Fmsy and estimated biomass is well above Bmsy. Trends indicate that fishing mortality has been and is still
decreasing, whilst biomass has been on the increase since 2005.
Management
less risk
more risk
The management of megrim in the northern North Sea and West of Scotland has been scored as low risk. This is because the stock
is assessed annually using the MSY approach and enforcement is considered adequate in the fishery.
Bycatch
less risk
more risk
The bycatch risk for this fishery has been assessed as high risk. Demersal otter trawling is known to have a high rate of bycatch of
non-target species. Some of these species are also non-commercial or protected and there is little information available as to the extent
of this side of discards.
Habitat
less risk
more risk
The seabed effects of the fishery are scored as high risk because demersal otter trawling has the potential to severely damage
benthic habitats. Demersal otter trawling is known to have an adverse impact on areas that have been trawled, however this may be
somewhat negated by the clearly defined fishing grounds as much of the seafloor remains relatively undisturbed by intense fishing
activity.
Outlook
Stock
Current risk status
Outlook
Reason
Very low
Stable/improving
The status of the stock is likely to stay very low
as the stock is being fished well below Fmsy
with fishing mortality on a decreasing trend
and biomass is well above Bmsy with an
increasing trend.
Management
low
Stable/improving
The stock is managed and assessed via a MSY
approach. There is currently no management
plan for Megrim in this area. Enforcement is
considered adequate.
Bycatch
High
Stable/improving
Demersal otter trawling has a high discard rate
in the mixed fishery in the North Sea
Habitat
High
Stable/improving
Demersal otter trawling has the potential to
severely damage benthic habitats, especially if
habitats are sensitive due to low levels of
natural disturbance
Type
Stock
Management
Bycatch
Habitat
Current Risk Status
Outlook
Reason
Stock Status Details
less risk
more risk
Time-trends
Catches of megrim have varied considerably over time with high landings recorded in the mid-nineties followed by a marked decrease to
the mid 2000’s. Since then landings have increased to roughly 3000 tonnes per year and have been around this since 2008. Fishing
mortality has been below Fmsy for nearly the whole time series since 1985 and has shown a decreasing trend since the late nineties.
Biomass has been above its corresponding MSYBtrigger value for the whole of the time series and since 2005 biomass has been estimated
to be increasing (Fig. 1) (ICES, 2015).
Figure 1. Megrim in Divisions IVa and VIa. Summary of
the stock assessment. Landings and discards are in
thousand tonnes. The available observed discard data
is included in the plot. Figures from ICES, 2015.
Discards of megrim is estimated to be approximately 15% since 2013. In 2014 of the 2809 tonnes of total catch in the northern North Sea
and west of Scotland, 309 tonnes of this was estimated discarded. According to ICES 87% of the 2500 tonnes landed was done so by otter
trawlers with cod end mesh sizes >100mm (ICES, 2015).
Stock structure and recruitment
For assessment purposes since 2011 ICES has defined megrim in the northern North Sea (ICES area IVa) and west of Scotland (ICES area
Via) as one stock. There is also another megrim (Lepidorhombus spp.) stock on the northern shelf at Rockall (ICES area VIb). Studies have
shown whilst there is a certain degree of connectivity between these stocks, there is spatial variation in biological characteristics such as
growth and spawning in addition to genetic differentiations as well (Macdonald et al., 2013; Macdonald & Prieto, 2013).
Data gaps and research priorities
According to ICES inaccurate and missing age data prevents an age based assessment, but if in the future data from surveys could be
stratified by depth and sex then an age based assessment model would be possible. In the past there has also been missing discard data,
with discards estimated at approximately 30% in the past. However they are assume to have declined to ~15% now and are now based
on observer data (ICES, 2015).
References
Gerritsen, H. D., McGrath, D., Lordan, C., & Harlay, X. (2010). Differences in habitat selection of male and female megrim (Lepidorhombus
whiffiagonis, Walbaum) to the west of Ireland. A result of differences in life-history strategies between the sexes?. Journal of Sea Research,
64(4), 487-493.
ICES (2007) Report on the Working Group on the Assessment of Northern Shelf Demersal Stocks (WGNSDS), Galway, Ireland. ICES
advisory committee on fisheries management. 868 pp.
ICES (2015) Megrim (Lepidorhombus spp.) in Divisions IVa and VIa (Northern North Sea, West of Scotland). ICES Advice 2015
Macdonald, P., Angus, C. H., & Marshall, C. T. (2013). Spatial variation in life history characteristics of common megrim (Lepidorhombus
whiffiagonis) on the Northern Shelf. Journal of sea research, 75, 62-68.
Macdonald, P. & Crego Prieto, V. (2013). Assessment of the population structure of common megrim (Lepidorhombus whiffiagonis) on the
Northern Shelf using genetic markers. NAFC Marine Centre report, 31p.
Macdonald, P., Angus, C. H., Cleasby, I. R., & Marshall, C. T. (2014). Fishers’ knowledge as an indicator of spatial and temporal trends in
abundance of commercial fish species: megrim (Lepidorhombus whiffiagonis) in the northern North Sea. Marine Policy, 45, 228-239.
Management Details
less risk
more risk
Advised and agreed catches
In 2014 total catch for megrim in northern North Sea (IVa) and waters west of Scotland (Via) was 2809 tonnes with 309 tonnes of this
discards. The whole megrim stock Is managed under a combined total allowable catch (TAC).
Catch 2014 (t)
Advised catch 2015 (t)
Agreed TAC 2015 (t)
Advised TAC 2016 (t)
2809*
7000**
6212**
5539**
*Total catch for the management unit comprising of ICES areas IVa and Via
** Catch is presented by ICES for the entire stock of megrim for all areas, agreed TAC is divided between ICES areas IIa and IV (2083
tonnes) and ICES areas Vb, VI, XII and XIV (4129 tonnes).
Stock harvesting strategy
Megrim in the northern North Sea (ICES area IVa) and west of Scotland (ICES area Via) is assessed annually. Biomass and fishing mortality
are estimated through a stock assessment model that uses both regional catches, observer collected discard estimates in addition to data
from six different surveys.
The fisheries for megrim in the management unit of the northern North Sea and west of Scotland is managed within the European Union
Common Fisheries Policy (CFP) through setting of annual TACs to keep fishing mortality and biomass above their respective reference
levels for MSY. Currently the most recent ICES advice indicates this management is working with fishing mortality well below Fmsy and
total stock biomass consistently above MSYBtrigger.
There is no specific management plan for megrim but the assessment is conducted with the MSY approach. Currently adult stock size is
high enough and fishing pressure low enough to lead to sustainable and optimal use in the future (ICES, 2015).
Surveillance and enforcement
Fisheries for megrim in Subareas IVa (northern North Sea) and and VIa (West of Scotlandl) are carried out by a number of countries and
surveillance activities to record compliance with national and international fishery control measures are primarily the responsibility of the
competent fishery inspection authorities in each country. In addition, the European Fisheries Control Agency (EFCA), established in 2005,
organises operational coordination of fisheries control and inspection activities by the Member States as well as cooperation with third
countries and other Regional Fishery Management Organisations.
The requirements for surveillance and sanctions for infringements are laid down in the EU Control Regulation (EC) No 1224/2009, which
amended previous similar regulations. Surveillance activities on fisheries that take megrim in the greater North Sea include the use of
vessel monitoring systems (VMS) on vessels over 12 m overall length, an electronic reporting system (ERS) and a vessel detection system
(VDS). Surveillance may also include direct observations by patrol vessels and aerial patrols; inspections of vessels, gear, catches at sea
and on shore; and verification of EU logbook data against sales documents. The control regulation specifies that member states should set
up electronic databases containing the inspection and surveillance reports of their officials as well as records of infringements.
Management controls are routinely enforced and independently verified through surveillance of fishing activities (e.g. VMS, logbooks,
dockside monitoring and visual inspections). Infringements happen only very occasionally and are unlikely to compromise harvest
objectives.
References
EFCA. [http://www.efca.europa.eu/] [Date accessed: 23-Dec-15]
ICES (2015) Megrim (Lepidorhombus spp.) in Divisions IVa and VIa (Northern North Sea, West of Scotland). ICES Advice 2015
Bycatch Details
less risk
more risk
Targeting and behaviour
Demersal otter trawling in the northern North Sea and west of Scotland targets the mixed fishery in the area. Gear towed can be twin or
single rig, with trawls doors and sweeps creating sand clouds that herd fish into the net (Løkkeborg, 2005).
In the North Sea and in west of Scotland the vast majority of megrim landings are from the larger mesh TR1 vessels. In the northern
North Sea, it is primarily Scottish vessels that land megrim to any extent. West of Scotland, Scottish vessel are also the primary fleet
landing megrim but France, Spain and Ireland also take notable shares of the landings (ICES, 2015).
Evidence of bycatch risk
Discard rates have been estimated from surveys at around 30-40% of total catch weight in European demersal otter trawl fisheries
(European Commission, 2011). Evidence collected from the Shetland Fishermen Tally book scheme indicated that approximately 41% of
the total catch was discarded on average, with the majority of this being commercial species (Napier, 2014)
However, evidence from TR1 vessels operating in the mixed fishery in the North Sea and west of Scotland in which megrim is caught
shows that the average discard rate for commercial species is markedly less than this. In the North Sea discard Atlas for example the
average discard rate by weight for Scottish TR1 vessels 2010-2012 was only ~16% for the commercial species caught (Anon., 2014a). West
of Scotland, of the EU countries that catch megrim in their TR1 fishery the discard rates for the majority of their catch are relatively low,
with the exception of cod. Cod in West of Scotland waters has a very high discard rate (Average for 2010-2012 for TR1 vessels = 86%) as a
result of the extremely low quota set for this particular area due to its stock status (Anon., 2014b).
Megrim specific discard rates are also estimated to be very low with majority of megrim caught being landed in both the TR1 and TR2
fisheries. Discards for megrim caught in the North Sea are estimated at approximately zero for both gears in 2010-2012. West of
Scotland the TR2 fleet catch is minimal of megrim but approximately zero were discarded in 2010 to 2012. The TR1 fleet discard rate for
megrim is estimated at approximately 4 % for 2010-2012. However discard information for megrim on the northern shelf has been
somewhat lacking until relatively recently so these discard rates may not be that reliable (Anon., 2014a; Anon., 2014b).
A study found that an increase in the TAC of megrim in recent years may have resulted in a significant reduction in discarding of the
species in the northern North Sea form ~54% in 2009 to ~20% in 2012 (Macdonald et al., 2014). More recent work by observers on board
Shetland vessels (fishing the northern North Sea) estimated the discard rate of megrim to be just 2.6% (Macdonald et al., 2015).
Mitigation measures
Due to the nature of a mixed fishery it is difficult to develop methods to improve the selectivity of vessels. The introduction of a 120mm
cod end mesh size for TR1 vessels went some way to releasing juvenile fish from the net whilst trawling and fishermen can also select
certain species to an extent by choosing area or grounds where they know a species is likely to be in higher abundance.
The cod recovery plan came into effect in its most recent incarnation in 2009, devised to bring about the recovery of cod stocks in the
North Sea, West of Scotland, Skaggerak Kattegat, the eastern channel and Irish Sea. Effort restrictions limit a vessel’s days at sea and
through a series of “buy backs” of more effort if member states fleets engage in cod avoidance measures such as spatial closures and
more selective gear (Kraak et al., 2013).
The Landings obligation more commonly known as the “discards ban” has come into effect for the demersal fisheries conducted within
the common fisheries policy as of January 2016. Currently there are only a number of commercial species where all catch must be
landed. For fisheries where megrim are caught these are haddock and plaice for the TR1 fleet and Nephrops for the TR2 fleet. Over the
course of the next few years more commercial species will be phased into the landings obligation with the intention of prohibiting
discarding of all catch quota species by 2019 (Marine Scotland, 2016).
References
Anon. (2014a). Discard Atlas of the North Sea Fisheries, August 2014, 80 pp.
Anon. (2014b). Discard Atlas of the North Western Waters Demersal Fisheries, Prepared by Cefas, Lowestoft, England. 14 December 2014,
118 pp.
ICES (2015). Megrim in Divisions IVa and VIa (Northern North Sea and West of Scotland). ICES Advice June 2015, Book 5, Section 5.3.22.
Kraak, S. B., Bailey, N., Cardinale, M., Darby, C., De Oliveira, J. A., Eero, M., … & Kirkegaard, E. (2013). Lessons for fisheries management
from the EU cod recovery plan. Marine Policy, 37, 200-213
Løkkeborg, S. (2005). Impacts of trawling and scallop dredging on benthic habitats and communities. FAO Fisheries Technical Paper 472.
Food and Agriculture Organisation of the United Nations, Rome, 58 pp.
Marine Scotland (2016). Demersal and Nephrops Landings Obligation form 2016, Marine Scotland guidance.
http://www.gov.scot/Topics/marine/Sea-Fisheries/discards/demersal [Accessed 14/03/2016]
Macdonald, P., Cleasby, I. R., Angus, C. H., & Marshall, C. T. (2014). The contribution of quota to the discards problem: a case study on the
complexity of common megrim Lepidorhombus whiffiagonis discarding in the northern North Sea. ICES Journal of Marine Science: Journal
du Conseil, 71(5), 1256-1265.
Macdonald, P., Batts, L. & Henderson, L. (2015) Data limited fish stocks in the northern North Sea. NAFC Marine Centre report. 72 pp.
Habitat Details
less risk
more risk
Gear effects, targeting and behaviour
Fishermen choose areas to fish based on their knowledge of the fishing grounds and previous catches. Technology on vessels that
indicates the depth and topography of the sea floor can also be used to identify potentially good fishing grounds as well. The gear may be
adapted slightly for alternative grounds where the benthic substrate differs. The majority of demersal otter trawling occurs on welldefined fishing grounds where fishermen’s catches are more predictable (Jennings & Lee, 2011).
Habitat risks
Bottom trawling is known to have sometimes serious adverse effects on the seafloor and the community living there. These effects range
from changing the habitat, altering food webs and endangering already vulnerable species. Modelling and field work on benthic habitats
in the North Sea found that bottom trawling altered biomass, production and species richness in the area (Hiddink et al., 2006; Johnson et
al., 2015).
Different habitats also tend to be effected to differing degrees. For example, habitats that are prone to high levels of natural disturbance
such as tidal and wave movement are less likely to be severely damaged by bottom trawling compared to habitat such as biogenic reefs or
mud where the level of natural disturbance is considerably lower (Hiddink et al., 2006; Jennings et al., 2012). This is also the case for
organisms that live in these habitats due to the greater resilience to disturbance found in fauna that live in areas with naturally high
disturbance (Bolam et al., 2014).
Mitigation measures
Under the Marine Strategy Framework Directive (MSFD) from the European Union (Council Directive 56/2008), Member States have
committed to aim towards ‘good environmental status’ (GES) for the seabed habitats by 2020. The Convention for the Protection of the
Marine Envrionment of the North-East Atlantic (the ‘OSPAR Convention’), which was signed up to by 15 nations plus the European Union, is
developing a coherent network of Marine Protected Areas to protect vulnerable marine habitats in the North-East Atlantic. The
development of offshore Special Areas of Conservation under the European Habitats Directive (Council Directive 43/1992) contributes to
this process as does the UK Marine Act designating Marine Protected Areas in UK waters. Networks of MPAs are currently being developed
around the UK coast, including in Division VIa.
References
Bolam, S. G., Coggan, R. C., Eggleton, J., Diesing, M. & Stephens, D. (2014). Sensitivity of macrobenthic secondary production to trawling in
the English sector of the Greater North Sea: A biological trait approach. Journal of Sea Research 85, 162–177.
Hiddink, J.G., Jennings, S., Kaiser, M.J., Queirós, A.M., Duplisea, D.E, and Piet, G.J. 2006. Cumulative impacts of seabed trawl disturbance on
benthic biomass, production, and species richness in different habitats. Canadian Journal of Fisheries and Aquatic Sciences 63: 721–736.
Jennings, S., Lee, J and Hiddink, J.G. (2012). Assessing fishery footprints and the trade-offs between landings value, habitat sensitivity and
fishing impacts to inform marine spatial planning and the ecosystem approach. ICES Journal of Marine Science 69(6) 1053-1063.
Johnson, A. F., Gorelli, G., Jenkins, S. R., Hiddink, J. G., & Hinz, H. (2015). Effects of bottom trawling on fish foraging and feeding.
Proceedings of the Royal Society of London B: Biological Sciences, 282(1799), 20142336.
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