Fishery Resources Monitoring System

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Norway lobster - North Sea, 2008
Marine Resource  Fact Sheet
ICES Advice 2009
Norway lobster - North Sea, 2008
Fact Sheet Citation  
Nephrops in Subarea IV (North Sea)
Owned byInternational Council for the Exploration of the Sea (ICES) – More
Related observationsLocate in inventorydisplay tree map
 
Species:
FAO Names: en - Norway lobster, fr - Langoustine, es - Cigala
Geographic extent of Norway lobster - North Sea
Main Descriptors
Considered a single stock: No        Spatial Scale: Sub-Regional
Management unit: Yes
 
 
Habitat and Biology
Depth zone: Shelf (50 m - 200 m).   Vertical distribution: Demersal/Benthic.  

Geographical Distribution
Jurisdictional distribution: Shared between nations

Water Area Overview
Spatial Scale: Sub-Regional

Geo References
Resource Structure
Considered a single stock: No
Exploitation
 

Factors affecting the fisheries and the stock

Regulations and their effects

The implementation of the “buyers and sellers” regulations in the UK in 2006 considerably tightened up the levels of reporting for Nephrops, and the landings figures since then are considered to be more reliable. Recent increases in landings and lpue may result from the increase in reporting levels and do not necessarily reflect changes to the stock.

A ban on the use of multi-trawl gears (3 or more trawls) for all Scottish boats was introduced from April 2008, limiting the expansion of effective effort.

Days-at-sea regulations and recently introduced effort allocation schemes (kW*day) have reduced opportunities for directed whitefish fishing. STECF 2008 stated that the overall effort (kW*days) by demersal trawls, seines and beam trawls shows a substantial reduction since 2002. However, there have also been substantial changes in the usage of the different mesh size categories by the demersal trawls. In particular there has been a sharp reduction in usage of gears with a mesh size of between 100mm and 119mm (targeting whitefish), and a subsequent general increase in effort by vessels using smaller mesh sizes (targeting Nephrops for instance) or larger (targeting whitefish).

The development of a Conservation Credits scheme in Scotland (the major contributor to landings from the Fladen Ground) requires all trawlers to implement more selective gears, including the use of 110 mm square mesh panels in 80mm gear. This measure aims to reduce catches (and discards) of small fish, including whiting, haddock, and juvenile cod.
Assessment
 
Assessment Model
Methodology

Scientific basis

Data and methods

Assessments of the Nephrops Functional Units of Subarea IV utilized a number of approaches, including Underwater UWTV surveys (UWTV) surveys, length composition information, and basic fishery data such as landings and effort. Owing to uncertainties in the accuracy of historic landings and to inaccurate effort figures in some fisheries, increasing attention is paid to survey information and size composition data as an indicator of stock status.

For those stocks without UWTV surveys, assessment is made on the basis of analysis of length compositions, trends in mean length for recruit classes and commercial CPUE. Biennial advice for these stocks was given in 2008 so no new advice is given this year.

There have been important developments in the methodology to assess the status of Nephrops stocks. The use of UWTV surveys has enabled the development of fishery-independent indicators of abundance. STECF (2005) had suggested that a combination of an absolute abundance estimate from an UWTV survey and a harvest rate based on F0.1 from a combined sex–length cohort analysis (LCA) and the mean weight and selection pattern from the commercial fishery could be used to calculate appropriate landings. The approach has been further developed and evaluated by ICES workshops in 2007 and 2009 (ICES, 2007, ICES 2009b). The 2009 workshop addressed concerns raised regarding factors which could potentially bias the UWTV survey results. Major sources of bias were quantified for each survey and an overall bias correction factor derived which, when applied to the estimates of abundance from the UWTV survey allows them to be treated as absolute abundance levels.

In particular the workshop concluded that the UWTV surveys detect the burrows of Nephrops considerably smaller than the sizes of those taken by the fishery. Therefore the abundance estimates used to calculate the Harvest Ratios presented in the 2009 advice include a component of the stock that is too small to be exploited by the fishery. This has resulted in calculated Harvest Ratios appearing to have decreased in the current advice compared to previous estimates of Harvest Ratios. In essence, this is a scaling issue, not a change in exploitation rate. The previous proportion corresponding to fishing at F0.1 were in the range of 15-20% whereas the revised values from the benchmark in 2009 are in the range of 8-10%.

Information from the fishing industry

Trends according to the North Sea fishers’ survey indicate disparate patterns of stock development. Long term increases in stock have been observed over most areas, but since 2007 the majority of areas show a small decline, except for Farn Deep (FU6) that shows a sharp decline (Figure 6.4.14.3).

Uncertainties in assessment and forecast

For moderate exploitation rates the UWTV assessment provides an adequate basis for predicting catches. ICES groups WKNephTV (ICES 2007), WKNephBid (ICES 2008b), SGNepS (ICES 2009a) have progressively worked to reduce uncertainty and increase precision in the interpretation of survey data.

There is a gap of at least 12 months (more commonly 18 months) between the survey and the start of the TAC year. It is assumed that the stock is stable during this period (i.e. recruitment and growth balance mortality). The effect of this assumption on realised harvest rates has not been investigated.

The UWTV survey does not cover the complete spatial distribution of the stock, covering 4 out of 8 Functional Units and not the area outside the Functional Units. The area covered by the UWTV survey accounts for 79% of the landings in 2008. Landings from outside the FUs account for 8% of total landings. Vessel Monitoring System (VMS) data for vessels > 15 meters are being successfully used to match survey and fishery areas.

The calculations of harvest ratio and F0.1 are all based on yield-per-recruit analyses from length cohort analyses. These analyses utilise average length frequency data taken over a 3 year period and therefore apply to stocks in equilibrium. However, it is unlikely that the Nephrops stocks to which the approach has been applied are actually in equilibrium due to variable recruitment. F0.1 estimates may vary in time due to changes in selection pattern.

Prior to the implementation of “Buyers and Sellers” legislation in 2006 reporting rates are considered to have been low and hence the estimated Harvest Ratios prior to 2006 are also likely to have been underestimated. The reliability of fishery statistics is improving but the transition period is accompanied in some cases by large changes in landings which produce significant changes in the lpue and cpue series that cannot be completely attributed to changes in stock. Until a sufficient time series of reliable data has built up, use of fishery catch and effort data in the assessment process should be avoided.

Comparison with previous assessment and advice

For those stocks without UWTV surveys, advice given in 2008 was biennial and therefore no new advice is given this year.

The advice basis for stocks with UWTV surveys has fundamentally changed since 2008. In 2008, ICES considered the UWTV indices to show relative trends and not absolute abundance. Consequently the advice was given in terms of maintaining landings at or below recent levels.
Overall Assessment Results


Figure 6.4.14.2 Nephrops in Subarea IV. Total landings divided into Functional Units and Other rectangles (tonnes).


Figure 6.4.14.3 Nephrops in Subarea IV. Results of the North Sea Commission fishers’ survey 2008.


Table 6.4.14.2 Nephrops in Subarea IV. Officially reported landings (tonnes) by Functional Unit plus Other rectangles.
Year FU 5 FU 6 FU 7 FU 8 FU 9 FU 10 FU 32 FU 33 Other IV Total
1981   1073 373 1006 1416 36     76 3980
1982   2524 422 1195 1120 19     157 5437
1983   2078 693 1724 940 15     101 5551
1984   1479 646 2134 1170 111     88 5628
1985   2027 1148 1969 2081 22     139 7386
1986   2015 1543 2263 2143 68     204 8236
1987   2191 1696 1674 1991 44     195 7791
1988   2495 1573 2528 1959 76     364 8995
1989   3098 2299 1886 2576 84     233 10176
1990   2498 2537 1930 2038 217     222 9442
1991 862 2063 4220 1404 1519 196     560 10824
1992 612 1473 3338 1757 1591 188     401 9360
1993 721 3030 3521 2369 1808 376 339 160 434 12759
1994 503 3683 4566 1850 1538 495 755 137 703 14230
1995 869 2569 6442 1763 1297 280 489 164 844 14717
1996 679 2482 5220 1688 1451 344 952 77 808 13701
1997 1149 2189 6171 2194 1446 316 760 276 662 15163
1998 1111 2177 5138 2145 1032 254 836 350 694 13736
1999 1244 2391 6505 2205 1008 279 1119 724 988 16463
2000 1121 2178 5580 1785 1541 275 1084 597 900 15060
2001 1443 2574 5545 1528 1403 177 1190 791 1268 15919
2002 1231 1953 7234 1340 1118 401 1170 861 1383 16691
2003 1144 2245 6305 1126 1079 337 1089 929 1390 15644
2004 1070 2152 8733 1658 1335 228 922 1268 1224 18590
2005 1058 3094 10685 1990 1605 165 1089 1050 1120 21855
2006 986 4858 10789 2458 1803 133 1028 1288 1249 24591
2007 1311 2966 11910 2652 1842 155 755 1467 1637 24695
2008* 695 1213 12240 2450 1514 173 675 1444 1673 22077
* Preliminary


Scientific Advice

Single-stock exploitation boundaries


Table 6.4.14.1 Nephrops in Subarea IV. Summary of the advice by Functional Unit plus Other rectangles.
Year

Moray Firth (FU9)

Noup (FU10)

Fladen Ground (FU7)

Nor-wegian Deeps (FU32)

Farn Deeps (FU6)

Firth of Forth (FU8)

Botney Gut-Silver Pit (FU5)

Off Horn’s Reef (FU33)

Other rec-tangles

2)

Total advice
5)

Agreed

TAC 1)

ICES landings
Mgt Area MA F MA G MA S MA I MA H        
1992 ~2.4 ~2.7   ~4.6 0.87   10.6 12.0 9.5
1993 2.4 2.7   4.17 0.87   10.2 12.0 12.7
1994 2.4 5.0   4.17 0.87   12.5 13.0 14.2
1995 2.4 5.0   4.17 0.87   12.5 15.2 14.7
1996 2.4 5.0   4.17 0.87   12.5 15.2 13.7
1997 2.4 5.0   4.17 0.87   12.5 15.2 15.2
1998 2.4 7.0   4.17 1.0   14.6 15.2 13.7
1999 2.4 7.0   4.17 1.0   14.6 15.2 16.5
2000 1.85 9.0   4.17 1.6   16.7 17.2 15.1
2001 1.85 9.0   4.17 1.6   16.7 15.48 15.9
2002 2.0 9.0 1.2 4.17 2.1   18.5 16.623 15.7
2003 2.0 9.0 1.2 4.17 2.1   18.5 16.623 15.6
2004 2.0 12.8 1.5 4.17 2.38   22.9 21.350 18.6
2005 2.0 <12.8 1.5 4.17 2.38   22.9 21.350 21.9
2006 - - NA - 2.38   NA 28.147 24.4
2007 2.4 0.2 <10.9 NA 3.5 1.5 NA NA 24.66) NA 26.144 24.6
2008 2.4 0.2 <10.9 NA 3.5 1.5 NA NA 9.56) NA 26.144 22.1
2009 < 1.8 < 0.24 < 11.3 --3 < 3.0 < 2.5 --3 --3 < 1.4 NA 24.837  
2010 <1.37 < 0.244 <16.4 --4 <1.2 <1.57 --4 --4 < 1.5 NA    

Weights in ‘000 t.

1) EU zone of Division IIa and Subarea IV.

2) Prior to advice for 2009, landings for other rectangles were included in 'Management Areas (MA)’.

3) No increase in effort.

4) Biennial advice given in 2008.

5) It is not advised to manage these stocks as a single unit.

6) refers to advice for FU 5, 32 and 33



Management
Management unit: Yes

Management Advice

Management considerations

Nephrops are limited to a muddy habitat. This means that the distribution of suitable sediment defines the species distribution and the stocks are therefore assessed as eight separate functional units (Figure 6.4.14.1):


SectionFU no. NameICES area Statistical rectangles
6.4.14.1*5 Botney Gut - Silver PitIVb,c 36-37 F1-F4; 35F2-F3
6.4.14.26 Farn DeepsIVb 38-40 E8-E9; 37E9
6.4.14.37 Fladen GroundIVa 44-49 E9-F1; 45-46E8
6.4.14.48 Firth of ForthIVb 40-41E7; 41E6
6.4.14.59 Moray FirthIVa 44-45 E6-E7; 44E8
6.4.14.6*10 NoupIVa 47E6
6.4.14.7*32 Norwegian DeeplVa 44-52 F2-F6; 43F5-F7
6.4.14.8*33 Off Horn ReeflVb 39-41E4; 39-41E5
* The advice for these stocks was given in biannual advice in 2008, see ICES (2008a).


Figure 6.4.14.1 Nephrops Functional Units in the North Sea and Skagerrak/Kattegat region (see Section 6.4.13).



An overview of advice for different functional units is presented in Table 6.4.14.1.

The overriding management consideration for these stocks is that management should be at the Functional Unit (FU) rather than the ICES Subarea level. Management at the Functional Unit level should provide the controls to ensure that catch opportunities and effort are compatible and in line with the scale of the resources in each of the stocks defined by the Functional Units. Current management of Nephrops in Subarea IV (both in terms of TACs and effort) does not provide adequate safeguards to ensure that local effort is sufficiently limited to avoid depletion of resources in Functional Units. In the current situation vessels are free to move between grounds, allowing effort to develop on some grounds in a largely uncontrolled way and this has historically resulted in inappropriate harvest rates from some parts. This is a particular problem in the Farn Deeps where increased vessel activity from other parts of the UK occurred resulting in low stock levels.

There are no precautionary reference points defined for Nephrops. This year ICES has provided advice on a range of catch options including a long term exploitation rate for Nephrops based on a number of considerations:

  • For many stocks ICES considers that exploitation rates between F0.1 and Fmax are an appropriate range of exploitation rates. For Nephrops both F0.1 and Fmax are often well defined.
  • There are a substantial number of studies on exploitation of fin fish indicating that F0.1 is consistent with maximising sustainable long term yield, though this has not been studied directly for Nephrops and further work is required to ascertain whether fishing at F0.1 is consistent with the management objective of maximising yield of Nephrops. Fmax is often considered too high an exploitation rate, leading to increasing risk to SSB without any substantial increases in yield. In addition for stocks with high discard rates a reduction of harvest rates often reduces the rates of exploitation of smaller individuals allowing larger numbers for the fishery in subsequent years.
  • A limited number of management simulations have been carried out (Dobby, 2007) on two of the FU in the NS showing that harvest ratios of close to F0.1 are appropriate for sustainable high long term yield with risks that ICES would consider precautionary. Ideally these simulations should be extended to other Nephrops FUs. The higher exploitation rates of the order of Fmax have not been explicitly tested but it’s unlikely that they will provide the same stability of yield and will have higher risks. These simulations did not explicitly deal with surveys that had different selection patterns from the fishery, there may be increases in risk associated with this, reinforcing the greater applicability of the lower exploitation rates.
  • For a number of FUs in the North Sea (and Celtic Seas) the recent catches have been substantially higher than the rates implied by F0.1. In the case of Firth of Forth (FU8) these catches have been even higher than the rate implied by Fmax but this coincided with an apparent increase in the stock in the last few years.


In light of the above considerations, ICES advises that F should be in the range of F0.1 to Fmax to maximize long term average yield without unduly risking SSB. ICES advice for individual functional units takes account of the current estimate of F and trend in SSB as follows:


F relative to F0.1 and Fmax

SSB

Stable or Increasing

SSB

Decreasing

F > FmaxReduce F to FmaxReduce F to F0.1
Fmax > F > F0.1Maintain current FReduce F to F0.1
F < F0.1Increase F to F0.1Maintain current F



Where the new advice suggests a large change in landings, a constraint on the year to year change in catches as is typical of management plans and the Communication on Fishing Opportunities for 2010 [COM (2009) 224] might be considered.

Some combinations of F and trend in SSB are included for completeness, even though not all of these combinations have been applied to North Sea Nephrops.

In general, catches of cod in the Nephrops fisheries have been relatively low, particularly in recent years in inshore grounds of Subarea IV, but can vary amongst Functional Units. However, it is important that emerging year classes of cod should not be subject to high discard mortality. The capture of juvenile fish or other species such as haddock is also a problem in some of the Functional Units and discarding of these is a problem in some years. This problem is being addressed with the use of more selective gear and efforts are already being made in Scotland through the Conservation Credits scheme, requiring vessels targeting Nephrops to use gear with larger square meshed panels (110 mm). Subject to evaluation of the effectiveness of these measures, further action may be required to reduce discards.

The advice is presented separately for each Functional Unit. In addition, there are increasing and significant landings from some isolated patches outside the Functional Units, most notably the Devil’s Hole area. Table 6.4.14.1 below shows that in 2008 overall landings in Subarea IV were around 22 100 tonnes, similar to landings in 2005. Landings from other rectangles have risen steadily and amounted to over 1 600 tonnes in 2008. To provide some guidance on appropriate future landings for these areas, the use of average landings of no more than 1500 tonnes (2006–2008) could be considered (Table 6.4.14.1).

Impacts of fisheries on the ecosystem

Trawling for Nephrops results in bycatch and discards of other species, including cod, haddock, and whiting. 80 mm is the predominant mesh size used in Nephrops fisheries and the resulting proportion of fish discarded can be high. Initiatives are in place to reduce discarding (see Regulations and their effects below).

The high mud content and soft nature of Nephrops grounds means that trawling readily marks the seabed, trawl marks remaining visible for some time. Burrowing fauna can be seen re-emerging from freshly trawled grounds, implying that there is some resilience to trawling.

Cod has been identified as a major predator of Nephrops in some areas. The generally low level of the cod in the North Sea is likely to have resulted in reduced predation. Multi-species models applied in the past to the exploitation of Irish Sea stocks indicated that management strategies which lead to an increase in the cod stock are associated with a reduction in Nephrops abundance. Therefore it may be expected that Nephrops stocks in the North Sea may decrease when cod recovers.
Biological State and Trend
Exploitation rate: Undefined
Abundance level: Undefined


Spawning biomass in relation to precautionary limits Fishing mortality in relation to precautionary limits Fishing mortality in relation to high long-term yield

Fishing mortality in relation to

agreed target

Comment

Unknown Unknown Unknown N/a  


Source of information
 
ICES.2009.Report of the ICES Advisory Committee, 2009. ICES Advice, 2009.
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