Download Nephrops in Botney Gut - Silver Pit, Demersal otter trawl

Nephrops in Botney Gut - Silver Pit, Demersal otter trawl
Nephrops in Botney Gut - Silver Pit, Demersal
otter trawl
Content last updated
14th Jan 2016
Stock:
Nephrops in Botney Gut - Silver Pit, Functional Unit 5
Management:
EU
Overview
The Norway Lobster (Nephrops norvegicus) is a decapod crustacean distributed throughout the North East Atlantic from Iceland and
northwest Norway, to the Atlantic coast of Morocco and the western and central Mediterranean. Nephrops construct burrows in muddy
seabed habitats in depths ranging from 20-800m, and emerge only to forage for food and to mate. Nephrops are only vulnerable to
fishing when outside their burrows.
Nephrops support extremely valuable fisheries and are caught mainly by demersal otter trawling, and also using traps or pots in some
locations. The Botney Gut and Silver Pit are in the central North Sea off east coast of England and NW coast of the Netherlands and
support a mixed trawl fishery using single and multi-rigged Nephrops trawls with codend mesh size 70-99mm as well as demersal trawlers
with codend mesh size >=120mm. The fishery is fished mainly by 10m vessels from Netherlands, UK, Germany and Belgium.
Mud patches with Nephrops populations are grouped into separate Functional Units (FUs) of which there are nine within the North Sea
(ICES Subarea IV): Moray Firth (FU9), Noup (FU10), Fladen Ground (FU7), Norwegian Deeps (FU32), Farn Deeps (FU6), Firth of Forth (FU8),
Botney Gut – Silver Pit (FU5), Off Horn’s Reef (FU33) and Devil’s Hole (FU34). Although the stock in each FU is assessed separately, and
ICES gives advice on landings of Nephrops according to single-stock advice, a single TAC is set for the whole of Subarea IV.
Figure 1. Nephrops
functional units (FU) (ICES,
2012)
References
ICES. 2012. ICES Advice 2013, Book 6, 2012. 6.4.14.1 Nephrops in Botney Gut – Silver Pit (FU5), pp. 19– 15.
ICES. 2014. ICES Advice 2015. Book 6, 2014. 6.3.15.1 Nephrops in the Botney Gut – Silver Pit (FU5), pp. 9 – 14.
Catchpole, T.L, Frid, C.L.J., Gray, T.S. 2006. Importance of discards from the English Nephrops norvegicus fishery in the North Sea to
marine scavengers. Mar Ecol Prog Ser 136: 1–3
Stock Status
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Nephrops in Botney Gut – Silver Pit, FU5 has been scored moderate risk. This is because Nephrops have a low vulnerability score of
Nephrops in Botney Gut – Silver Pit, FU5 has been scored moderate risk. This is because Nephrops have a low vulnerability score of
14/100 but have unknown stock size (B) and harvest rate (F) trends for this functional unit due to as yet insufficient time series data.
Management
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Nephrops in Botney Gut – Silver Pit, FU5 has been scored moderate risk. This is because whilst the functional unit is assessed annually
by ICES, the TAC is set for SubArea IV as a whole, which can lead to uncontrolled increases in fishing effort in individual functional units.
Surveillance is generally effective with adequate enforcement and compliance.
Bycatch
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The bycatch risk of this fishery are scored very high risk. This is because the bycatch and reported discard rates are high (>50%) in
Nephrops trawls due to the small cod end mesh requirements of the target species. However, measures to reduce bycatch and discards
in these fisheries have been the subject of much research over the years, resulting in technical measures which improve selectivity, which
in turn have been implemented as a statutory requirement. Further measures, such as modified trawl designs, have been implemented
on a non-statutory basis.
Furthermore, the cod recovery plan has been implemented in this area and this is expected to have had an influence on the discarding
levels in North Sea demersal fisheries and the incoming EU landings obligation is also intended to reduce discarding.
Habitat
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The habitat risk of this fishery has been scored a high risk. This is because, there is the potential for this fishery to interact with
vulnerable marine habitats within the core fishing areas. Spatial management to reduce these interactions is being developed, as there
remains some uncertainties about the location of sensitive seabed habitats so these remain at risk.
Outlook
Stock
Current risk status
Outlook
Moderate
Stable
Reason
The population status is unknown,
however catch rates are stable and harvest
rates are well below those required for
Maximum Sustainable Yield F(MSY)
Management
Moderate
Improving
The CFP is going through reform and there
is some uncertainty on how this will impact
fisheries management in the North Sea.
Continued use of UWTV surveys will allow
the stock to be declassified from its current
data limited status and assessed with
respect to quantitative biological reference
points.
Bycatch
Very high
Improving
Nephrops otter trawls have the potential to
interact with vulnerable habitats, but there
is some spatial management with in the
footprint of this fishery which provides
protection to identified vulnerable marine
habitats. Management measures are
continuously being developed and could
reduce the risk further.
Habitat
High
Improving
Nephrops otter trawls have the potential to
interact with vulnerable habitats, but
spatial management measures are
continuously being developed and will
likely reduce the risk.
Stock Status Details
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Time-trends
Reported landings were predominantly from Belgium with smaller amounts from Denmark until 1995. From 1995, landings showed a step
increase due to entry to the fishery from the Netherlands UK and Germany. The relative proportion of landings from the UK has gradually
increased against decreasing Belgium landings, however overall international landings have otherwise remained largely stable.
Figure 1.Time series of international landings
from 1991.
The major Nephrops stocks in the North Sea are surveyed using an underwater television system to estimate stock size. Cameras are
towed over the seabed allowing scientists to directly count the density of Nephrops burrows. These densities are then scaled up to
estimate the stock abundance and biomass (B) for each FU. No underwater television (UWTV) survey is routinely carried out for this unit
however a preliminary survey in 2012 indicated densities to be around 0.7 Nephrops burrows per square metre, towards the upper end
of all burrow densities observed.
Harvest rate from fishing (F) has been below Fmsy (harvest rate for maximum sustainable yield) for both of the assessed years, however,
along with the estimate of biomass from the UWTV survey, there has not yet been an appropriate amount of time to infer the underlying
trend in the population, the status of which must be described as unknown.
Stock structure and recruitment
Nephrops require sediment with a silt & clay content of between 10 – 100% to excavate burrows, and the locations of suitable sediments
defines the distribution of the species. There are nine discrete populations in Subarea IV, referred to as functional units (FU), and these are
assessed as independent stocks. The Botney Gut – Silver Pit stock, FU5, inhabits an area of 1850km2 (ICES 2014).
Changes in recruitment can be inferred from trends in size compositions of catches, but there is no survey or assessment model to
generate a time series of recruitment indices.
Nephrops are omnivorous feeding on polychaetes, crustaceans, molluscs and echinoderms and are predated upon by large gadoids,
particularly cod, however generally low levels of cod in recent years have likely resulted in reduced predation.
Females mature at approximately 3 years of age, and during the egg incubation period they leave the burrows less frequently and
commercial catches become dominated by males. Larvae are pelagic for one month after hatching and after metamorphosis the small
Nephrops settle on the sea bed.
Data gaps and research priorities
Techniques are currently employed during UWTV surveys to distinguish burrow systems which may have multiple entrances, and
occupancy of burrow systems can be established by examining the state of the burrows which quickly collapse if left unattended for any
time. The occupancy rate is assumed to be one individual per burrow system, however to some extent this remains an unknown quantity,
and other clawed lobster species (Homarus spp.) are known to cohabit burrows for short periods around mating. Sex composition of
burrow occupants, whilst assumed to favour incubating females, is poorly known.
The skewed sex distribution in some fisheries has the potential to impact upon reproduction success, particularly where the fishery is
male dominated. The extent to which this is realised is not known but may influence the Botney Gut – Silver Pit stock.
Eventual implementation of the Landings Obligation rules (EU 1380/2013) may affect harvesting practices. Although ICES advised for the
first time this year based on both implementation and non-implementation of the rules with respect to Nephrops, it remains to be
ascertained what secondary effects may derive from the requirement to land bycatch of quota finfish species.
References
Catchpole, T.L, Frid, C.L.J., Gray, T.S. 2006. Importance of discards from the English Nephrops norvegicus fishery in the North Sea to
marine scavengers . Mar Ecol Prog Ser 136: 1–3
ICES. 2012. ICES Advice 2013, Book 6, 2012. 6.4.14.1 Nephrops in Botney Gut – Silver Pit (FU5), pp. 9 – 15.
ICES. 2014. ICES Advice 2015. Book 6, 2014. 6.3.15.1 Nephrops in Botney Gut – Silver Pit (FU5), pp. 9 – 14.
Management Details
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Advised and Agreed Catches*
Landings 2013 (t)
Advised catch 2015 (t)
Agreed TAC 2015 (t)
Advised catch 2016 (t)
1050**
1159t (1043t***)
17843t****
1159t (1043t***)
* Advice for this FU is produced biennially and has not been updated this year
** 2013 landings provisional and do not include discards (estimated at 10% by weight)
*** Advised catch for 2015 and 2016 of 1159t comprising 1043t of landings
**** TAC is set for EC waters of the entire SubArea IV
Stock Harvesting Strategy
The Nephrops stocks in the Botney Gut – Silver Pit are assessed under a data-limited approach using commercial catches comprising
inputs of international landings, Dutch discards and length frequencies from catch sampling.
ICES gives advice for Nephrops FUs according to harvest rates (ratio of catch size to population size) that provide Maximum Sustainable
Yield (MSY). Since Botney Gut – Silver Pit is assessed as a data-limited stock, the lower boundary of MSY harvest rates is used as an upper
limit for advice. This equates to landings of no more than 8% of the stock abundance. The harvest rate includes discards, from which
survival is assumed to be zero. The ICES Data Limited approach for Nephrops advice is to use the lowest value of either the mean landings
over the previous 10 years or the landings equating to the MSY harvest rate on the proxy abundance. The 10 year average landings are
currently 1043 tonnes, equating to a harvest rate of 2.4%.
Nephrops in Botney Gut – Silver Pit, FU5 are assessed biennially to estimate abundance and fishing mortality. ICES advice for most of the
North Sea FUs is based on stock assessments using time-series of population estimates calculated from camera surveys, with the mean
burrow density in the Botney Gut – Silver Pit of 0.70 burrows per square metre being considered towards the upper end of the range
observed for all FUs The assessments use international landings and discards in conjunction with the TV surveys to calculate a harvest
rate, however TV surveys in Botney Gut – Silver have only been carried out twice, in 2010 and 2012, and as yet do not form a sufficient
time series which to infer trends. Therefore, in absence of a full analytical assessment, the MSY harvest rate reference point is set at the
lower boundary of the MSY harvest rate estimates for other FUs, or 8%. The fisheries for Nephrops in the North Sea are managed under
the EU Common Fisheries Policy (CFP) primarily through annual TACS (Council Regulation (EC) 1380/2013) set for the North Sea as a
whole. Nephrops otter trawls with mesh size 70-99mm are included in the regulated TR2 gears subject to effort (kw-days) controls in
relation to gear group, mesh size and catch composition specified in the EU long term cod management plan since 2008 (Council
Regulation (EC) 1342/2008 and 1243/2012).
These controls do not provide adequate safeguards to avoid depletion of Nephrops in any functional unit. Vessels are free to move
between grounds, subject to any specific access requirements, allowing effort to develop on some grounds in a largely uncontrolled way.
This has historically resulted in inappropriate harvest rates from some FUs. Although harvest rates on Botney Gut – Silver Pit Nephrops
have been well below the FMSY reference point for all of the last 10 years, there is no direct mechanism to manage fishing effort in this FU
to ensure the harvest rate remains as such.
Surveillance and Enforcement
Landings are monitored from EU logbooks and in the UK, from sales notes. Discards are estimated by observers on randomly selected
vessels.
There are no specific EU or national management objectives for Botney Gut – Silver Pit Nephrops. Generic technical measures for the
North Sea include an EU minimum landing size for Nephrops of 25mm carapace length. Almost all the Nephrops landings from the Botney
Gut – Silver are made by Netherlands, UK, Belgium and Germany vessels, with very small amounts taken by vessels from Denmark.
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. The requirements for surveillance and sanctions for infringements are laid down
in the EU Control Regulation (EC) No 1224/2009. Surveillance activities on the Botney Gut – Silver Pit fishery include the use of vessel
monitoring systems (VMS) on vessels over 12m overall length; an electronic reporting system (ERS) and a vessel detection system (VDS) for
over 12m vessels and, from the UK, the fishery has been exclusively fished by such vessels for all of the last 10 years. With all of the
vessels In England, the Navy and Marine Management Organization are variously responsible for surveillance activities using patrol vessels
and/or aerial patrols, inspection of vessels, gear and catches at sea and on shore, and verification of EU logbook data against sales
documents. The EU 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. In the UK, it is understood that catch reporting has improved
since 2006 when the Registration of Buyers and Sellers scheme was implemented, and has probably improved further by more
widespread use of electronic logbooks and reduction in vessel length for mandatory VMS deployment from 15m to 12m.
References
ICES. 2014a. Report of the ICES Advisory Committee 2014. ICES Advice, 2014. Book 6.
Bycatch Details
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Targeting and behaviour
Demersal otter trawls targeting Nephrops operating in this area can be towed by a single boat as a single or multiple rig. Gears are
adapted to the substrate type and the species targeted, with a relatively narrow range of conditions in which they can operate. Generally
the sweeps are shorter on Nephrops trawls than on those designed to catch fish, since unlike fish, Nephrops are not herded into the path
of the trawl.
Skippers will use information available to them to choose known tow locations within the mud patch where catch rates and catch
compositions are likely to be favourable, whilst taking into account other operational factors such as vessel size, weather, tide and fuel
costs.
Demersal otter trawling is not a well targeted fishing activity given that a wide variety of non-target species can be caught. As well as
Nephrops, this fishery catches a wide variety of mixed demersal finfish, such as Atlantic cod (Gadus morhua), haddock (Melanogrammus
aeglefinus) and whiting (Merlangius merlangus), and these mixed catches means that the minimum cod end mesh size of 80 mm and
other aspects of the management regimes and markets are not optimal for all the species caught. Fish may be discarded because they
are smaller than the Minimum Conservation Reference Size, or the size and/or species are not marketable. Discarding due to the vessel
being short of quota for the managed species also occurs.
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). A characteristic fish and invertebrate fauna tends to occur on Nephrops fishing grounds, however the
quantity and composition of bycatch will vary considerably between Functional Units within the North Sea. The Discards Atlas for the
North Sea demersal fisheries (Anon, 2014) shows 64% of the combined catch of the top six species taken by small mesh otter trawls (80 –
99 mm mesh size; including the category used for Nephrops ) in the North Sea during 2010-2012 was discarded. The largest amounts
discarded amongst these species were dab, plaice, whiting and haddock.
Nephrops fisheries have a small bycatch of elasmobranch species including skates, rays and sharks (particularly spurdog). These species
have a relatively large size at maturity and low numbers of young (low fecundity) and are considered more vulnerable to fishing than the
more fecund teleost (gadoid) stocks such as whiting and haddock. There are prohibitions on landing those which are most depleted. This
helps conserve stocks, because these species have good survival potential (Enever, et al., 2009).
Mitigation measures
A wide variety of non-target species are caught in European mixed otter trawl fisheries. Optimising gear selectivity in mixed fisheries is
challenging given that different species have different selectivity requirements.
Many measures have been designed and tested to increase selectivity in Nephrops trawls (Catchpole and Revill, 2008). Some have been
implemented as compulsory in the Nephrops North Sea fishery such as the use of sorting grids or 120 mm square mesh panels (EU
227/2013).
There are also measures nationally to control cod end twine thickness and design, intended to counter measures to reduce selectivity and
there is some voluntary uptake of trawl designs that have been tested to reduce discards, for example the ‘coverless’ trawl designed and
tested by Seafish (UK) and fully described in Dunlin & Reese (2003) and Revill et al. (2006).
A bycatch reduction scheme (Commission Regulation (EU) 724/2010, Norwegian Marine Fisheries Act 2008) allows real time closures of
areas has been enacted to protect juvenile gadoid (cod, haddock, saithe and whiting) when the catch rates of those juveniles becomes too
high.
The cod recovery plan (EU 1342/2008) which is in force in North Sea, Eastern English Channel, Irish Sea, West of Scotland and the
Skagerrak, has encouraged a diversity of measures to incentivise the use of more selective gear by vessels targeting whitefish with
demersal otter trawls. Effort per vessel is limited to a number of days at sea per year. Additional days at sea are available for vessels using
certain specified gears and measures, tested for their efficacy at improving selectivity.
The different European Nations have implemented different measures in their fisheries, described below are measures implemented in
the UK fisheries.
Real time closures
The cod avoidance plans also include ‘real time’ closures of areas where concentrations of cod are found. Since 2007 UK administrations
have operated these areas for UK vessels in the North Sea and English Channel in response to concentrations of juvenile cod; when a
vessel catches more than threshold number of cod per hour agreed by a boarding officer and the skipper or concentrations of adult cod
through analysis of landings and Vessel tracking data (VMS). The size and duration of the closure varies according to administrative body.
This a similar scheme to designed operated under European legislation (EU 783/2011) which is designed to protect juvenile cod, saithe,
haddock and whiting and there are also seasonal closures to protect spawning stocks (See Marine Scotland and Marine Management
organisation websites).
It has proved difficult to quantify the efficacy of each of these measures, however ‘it seems likely that cod avoidance measures have
contributed significantly to the reduction in the discard rate of cod’ in the North Sea fishery (Anon, 2014).
Landings obligation
The introduction of the landings obligation or ‘discard ban’ under the EU Common fisheries policy (EU 1380/2013) is intended to take place
over the period 2016 – 2019 in this fishery. This landings obligation will ultimately apply to all species managed by TAC; it will not apply to
non-TAC species, however many of these are likely to benefit from improved selectivity.
References
Anon. 2014. Prepared by Scheveningen group, Discard Atlas for the North Sea Demersal Fisheries.
Catchpole, T. L., & Revill, A. S. 2008. Gear technology in Nephrops trawl fisheries. Reviews in Fish Biology and Fisheries, Volume 18(Issue 1),
17–31.
Dunlin, G. and Reese, R., (2003) Financial Instrument for Fisheries Guidance (FIFG) Project, An Industry-centred conservation project –
Commercial proving trials of a new prawn trawl design, SFIA, Seafish Report, 551.
Enever, R., Catchpole, T. L., Ellis, J. R., & Grant, A. 2009. The survival of skates (Rajidae) caught by demersal trawlers fishing in UK waters.
Fisheries Research, 97(1-2), 72–76. doi:10.1016/j.fishres.2009.01.001
European Commission, 2011. Impact Assessment of Discard Reducing Policies, Common fisheries policy impact assessment. EU Discard
Annex. Studies in the Field of the Common Fisheries Policy and Maritime Affairs. Lot 4:
[http://ec.europa.eu/fisheries/documentation/studies/discards/report_en.pdf] [Date accessed: 07-Jan-16]
Revill, A., Dunlin, G., Holst, R. 2006. Selective properties of the cutaway trawl and several other commercial trawls used in the Farn Deeps
North Sea Nephrops fishery. Fisheries Research, 81 (2-3), pp. 268-275
Habitat Details
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Targeting and Behaviour
Fishermen use their knowledge of seabed types and prime Nephrops grounds together with information from the vessel’s electronic
mapping tools to make informed decisions on where to trawl. Gears are adapted to the substrate type and the species targeted, with a
relatively narrow range of conditions in which they can operate. Generally the sweeps are shorter on Nephrops trawls than on those
designed to catch fish, since unlike fish, Nephrops are not herded into the path of the trawl.
Evidence of habitat risk
Nephrops grounds generally contain a range of burrowing fauna including Nephrops and species of fish and shrimps. There are some
areas inhabited by sea pens, slender colonial hydroids which protrude from the mud surface. Effectively the burrowing activities of the
fauna form a structure within which other marine life can live. The passage of trawlers’ ground gear, clumps (in the case of twin rig) and
doors over Nephrops’ burrows may close up their entrances. Provided the animals are not injured, they have been observed to be able to
open up the burrows again (Coggan, Smith, & Moore, 2001). Thus apart from the energy cost in burrow maintenance, the direct effects of
trawl passage on uncaught Nephrops may be minimal.
However, the mechanical disturbance of the gear on the seabed is likely to affect the structure of the burrowed mud community. There
have been ecological effects on benthic communities observed which have been related to the amount of Nephrops trawling over a long
period. The effects include changes in species composition and biodiversity (Hinz, Prieto, & Kaiser, 2009).
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 Environment of the North-East Atlantic (the ‘OSPAR Convention’), which was signed up to by 15 nations including Norway plus the
European Union, is developing a coherent network of Marine Protected Areas to protect vulnerable marine habitats in the North-East
Atlantic and the development of related areas under the European Habitats Directive (Council Directive 43/1992) contributes to this
process as does the UK Marine Act and Marine Scotland Act designating Marine Protected Areas in UK waters.
These initiatives have resulted in improvements in habitat mapping and risk assessment of the effects of trawling on the seabed as well as
measures to implement management measures where sites are considered at risk.
References
Coggan, R. A., Smith, C. J., & Moore, P. G. (2001). Final report; Comparison of rapid methodologies for quantifying environmental impacts
of otter trawls Final report DG XIV Study Project 98/017 (p. 254).
Hinz, H., Prieto, V., & Kaiser, M. J. (2009). Trawl disturbance on benthic communities: chronic effects and experimental predictions.
Ecological Applications : A Publication of the Ecological Society of America, 19(3), 761–73.
[http://www.ncbi.nlm.nih.gov/pubmed/19425437] [Date accessed: 31-Jan-15]
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