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Spring Spawning Herring - Skagerrak and Kattegat
Marine Resource  Fact Sheet
ICES Advice 2009
Spring Spawning Herring - Skagerrak and Kattegat
Fact Sheet Citation  
Herring in Subdivisions 22-24 and Division IIIa (Spring spawners)
Owned byInternational Council for the Exploration of the Sea (ICES) – More
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Species:
Species thumbnail
Clupea harengus
FAO Names: en - Atlantic herring, fr - Hareng de l'Atlantique, es - Arenque del Atlántico, ru - Сельдь атлантическая
Geographic extent of Spring Spawning Herring - Skagerrak and Kattegat
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Main Descriptors
Considered a single stock: Yes        Spatial Scale: Sub-Regional
Management unit: Yes         Reference Year: 2008
 
Table of Contents
Habitat and Biology - Geographical Distribution - Water Area Overview -  Management - Assessment - Exploitation - Biological State and Trend - Source of information
 
Habitat and Biology
Depth zone: Shelf (50 m - 200 m).   Vertical distribution: Pelagic.  

Geographical Distribution
Jurisdictional distribution: Shared between nations

Water Area Overview
Spatial Scale: Sub-Regional

Geo References
Resource Structure
Considered a single stock: Yes
Exploitation
 

Factors affecting the fisheries and the stock

Regulations and their effects

Corrections for misreporting by area have been incorporated in the assessment. In recent years, ICES has calculated that a substantial part of the catch reported as taken in Division IIIa by fleet C was actually taken in Subarea IV. These catches have been allocated to the North Sea stock and accounted for under the A fleet. Regulations allowing quota transfers from Division IIIa to the North Sea were introduced as an incentive to decrease misreporting for the Norwegian part of the fishery. Recent Working Group estimates of 30% misreporting in Division IIIa may be underestimating the problem because not all countries supply this information to ICES.

The quota for the C fleet and the bycatch quota for the D fleet (see above) are set for the NSAS and the WBSS stocks together. The implication for the catch of NSAS must also be taken into account when setting quotas for the fleets that exploit these stocks.

Changes in fishing technology and fishing patterns

There have been only minor changes in the fishery technology in recent years.

Impact of the environment on the fish stock

Herring in Division IIIa and Subdivisions 22–24 are migratory. There are feeding migrations from the Western Baltic into more saline waters of Division IIIa and the eastern parts of Division IVa. There are indications from parasite infections that yet unknown proportions of sub-stocks spawning at the southern coast in the Baltic proper may perform similar migrations.

Western Baltic herring recruitment has been reduced by 15–35% annually from 2004 onwards and is now at a record low. North Sea herring, with which Western Baltic herring shares the same environment at least for part of the year, has also produced only very small year classes since 2002. In a recent recruitment analysis for different Baltic herring stocks, the Baltic Sea Index (BSI) reflecting Sea Surface Temperature (SST) was the main predictor for Western Baltic herring (Cardinale et al., in press). There are no indications of systematic changes in growth or age at maturity, and candidate key stages for reduced recruitment are probably the egg or the larval stage. The specific reasons for reduced egg or larval survival are not known. Further investigation of the causes of the poor recruitment will require targeted research projects.
Assessment
 
Assessment Model
Methodology

Scientific basis

Data and methods

The otolith microstructure method has been used to calculate the proportion of spring and autumn spawners caught in these areas for all catch and survey data in the period 1991–2008. An analytical FLICA assessment is based on catch data and the results of two acoustic and one larval survey.

Information from the fishing industry

VMS data confirm that area misreporting from the North Sea to the Skagerrak has declined in proportion with the reduction in reported landings. Identified misreported catch has been moved to the appropriate areas and are thus taken into account in the assessment.

Uncertainties in assessment and forecast

There is no firm basis to predict the fraction of NSAS in the catches by the C- and D-fleets. The proportions of the two stocks as well as the distribution pattern of the fishery in the Eastern North Sea and in Division IIIa changes dynamically year by year. This is probably influenced by the year class strength of the two stocks and their relative geographical distributions, as well as by fleet behavior reacting to herring availability and management decisions.

The strength of a year class is not firmly estimated before the year class has been followed for 2–3 years. However, the introduction of a larval 0-group recruitment index (N20) in 2008 appears to contribute valuable and consistent information to the estimate of the 1-winter ringers in the assessment.

Comparison with previous assessment and advice

A benchmark assessment was carried out in 2008. The update assessment this year shows a reduction of 23% of the estimated fishing mortality in 2007 and a 21% increase for the SSB in 2007. However trends in recruitment and SSB are similar.

In 2008 ICES advised an immediate reduction in F to candidate for Fmsy = 0.25. In the light of the continuing reduction of recruitment, the basis for the advice did not change.
Overall Assessment Results


Figure 6.4.15.1. Herring in Subdivisions 22–24 and Division IIIa (spring spawners). Landings, fishing mortality, recruitment, and SSB. Estimates are shown in grey. 2009 recruitment taken as GM 2003–2007.
Figure 6.4.15.2. Herring in Subdivisions 22–24 and Division IIIa (spring spawners). Stock recruitment, yield and SSB per recruit, precautionary approach.


Figure 6.4.15.3. Herring in Subdivisions 22–24 and Division IIIa (spring spawners). Historical performance of the assessment. The last data point for SSB is a prediction, for Recruitment the last data points is GM 03-07.


Table 6.4.15.2. Herring in Subdivisions 22–24 and Division IIIa (spring and autumn spawners). Landings (‘000 t).


Table 6.4.15.3. Herring in Subdivisions 22–24 and Division IIIa (spring spawners). Summary of the assessment.
Year Recruitment SSB Landings Mean F
  Age 0 at spawning time   Ages 3-6
  thousands tonnes tonnes  
1991 5003979 310543 191573 0.3576
1992 3652584 322123 194411 0.4762
1993 3109372 295303 185010 0.5439
1994 6182874 231273 172438 0.6894
1995 4050991 183178 150831 0.5121
1996 4472243 134412 121266 0.7007
1997 3991042 150554 115588 0.5097
1998 5585578 121510 107032 0.4919
1999 6439794 128418 97240 0.3730
2000 3444329 141946 109914 0.4661
2001 4448602 162715 105803 0.4537
2002 3057143 201961 106191 0.4102
2003 4039490 162065 78309 0.3944
2004 2655128 167171 76815 0.3577
2005 2226088 165281 88406 0.4073
2006 1813432 192109 90549 0.3959
2007 1259682 161537 68997 0.3576
2008 894443 159406 68484 0.3670
2009* 2225068 141824    
Average 3607756 185965 118270 0.4591
* Recruitment is GM (2003–2007). SSB is predicted.

Reference Point
 

There are no precautionary approach reference points agreed for this stock.
Yield and spawning biomass per Recruit F-reference points (2009):
  Fish Mort Yield/R SSB/R
  Ages 3-6    
Average last 3 years 0.37 0.03 0.06
Fmax* - - -
F0.1 0.23 0.03 0.09
Fmed 0.39 0.03 0.05
*Fmax is not well defined.

Candidates for reference points consistent with high long-term yields and a low risk of depleting the productive potential of the stock are around F0.1. Preliminary HCR evaluations are consistent with this view and have shown that candidates for Fmsy can be found in the region of F = 0.25 (see Section 8.3.3.1).
Projection

Outlook for 2010

To derive the total herring catch for Division IIIa (right hand side of the table), predicted catches of NSAS (as advised in Section 6.4.16) have to be added to the advised maximum catches of WBSS in the area. The total catch by fleet is only compatible with the advice for WBSS if the values given for NSAS are treated as maximum catches. Thus the resulting catch options were also used as constraints for catch options for the NSAS herring (Section 6.4.16). Note that the right hand side of the table is for illustrative purposes only and is not part of the ICES advice; the ratio of TACs between areas is not fixed and there are several options for TACs compatible with the removal of WBSS advised by ICES.
Explanation on fleet coding:
Area Fleet Description
North Sea A Directed herring fisheries with purse-seiners and trawlers. Bycatches in industrial fisheries by Norway are included.
  B Bycatches of herring taken under EU regulations.
Division IIIa C Directed herring fisheries with purse-seiners and trawlers.
  D Bycatches of herring caught in the small-mesh fisheries.
Subdivisions 22-24 F All herring fisheries in Subdivisions 22–24.

Catch options for mixed stocks in Division IIIa based on short-term predictions for Western Baltic Spring-Spawning herring (WBSS)

Catch options for the whole stock of Western Baltic Spring-Spawning herring (WBSS) can be partitioned into catches by area. Catches of WBSS herring in Division IIIa also imply catches of North Sea Autumn-Spawning (NSAS) herring which constitute part of the total catch in that area.

ICES catch predictions versus management TAC

ICES advises on catch options by fleet for the entire distribution of the two herring stocks separately, whereas herring is managed by areas cross-sectioning the geographical distribution of the stocks (see the following text diagram).

The catch options for 2010 are based on the TAC proportions by fleet and area in 2009 and, for IIIa, on the observed stock composition (WBSS vs. NSAS) in catches taken in 2008. Short-term predictions are based on an expected catch in 2009 of 45 087 t of Western Baltic spring spawning stock taking into account the TACs by fleet for 2009, potential misreporting and the assumed proportion of Western Baltic spring spawning herring in the catches in Division IIIa.

To make fleet wise catch options for the prediction year it is assumed that the TAC distribution by fleet in 2010 will be equal to 2009. It is also assumed that there will be allowed a subtraction of 20% of the Norwegian quota that is transferred to the A-fleet (as NSAS). Further it is assumed that each fleet catches its total TAC. Finally it is assumed that the 2008 proportions of WBSS by fleet hold for 2010. The proportions of WBSS in catches were 0.71 in the C-fleet, 0.37 in the D-fleet and 1.00 in the F-fleet and further a constant catch of 120 t of WBSS caught in the A-fleet in Division IVa East.
Scientific Advice

Single-stock exploitation boundaries

ICES advises on the basis of exploitation boundaries in relation to long-term yield that fishing at the candidate Fmsy fishing mortality (0.25) implies catches in 2010 not larger than 39 800 t in the entire distribution area.


Table 6.4.15.1. Herring in Division IIIa and Subdivisions 22–24 (Western Baltic spring spawners). Single stock exploitation boundaries (advice), management and catches.
Year ICES
Advice		 Pred. catch
corresp.
to advice		 Agreed
TAC IIIa2		 ICES catch of
Stock
        22–24 IIIa IV Total
1987 Reduction in F 224 218 102 59 14 175
1988 No increase in F 196 218 99 129 23 251
1989 TAC 174 218 95 71 20 186
1990 TAC 131 185 78 118 8 204
1991 TAC 180 155 70 112 10 192
1992 TAC 180 174 85 101 9 195
1993 Increased yield from reduction in F; reduction in juvenile catches 188 210 81 95 10 186
1994 TAC 130–180 191 66 92 14 172
1995 If required, TAC not exceeding recent catches 168–192 183 74 80 10 164
1996 If required, TAC not exceeding recent catches 164–171 163 58 71 1 130
1997 IIIa: managed together with autumn spawners
22–24: if required, TAC not exceeding recent catches		 66–851 100 68 55 1 124
1998 Should be managed in accordance with North Sea autumn spawners - 97 51 53 8 112
1999 IIIa: managed together with autumn spawners
22–24: if required, TAC not exceeding recent catches		 - 99 50 43 5 98
2000 IIIa: managed together with autumn spawners
22–24: if required, TAC not exceeding recent catches		 ~60 for Subdivs. 22–24 101 54 57 7 118
2001 IIIa: managed together with autumn spawners
22–24: if required, TAC not exceeding recent catches		 ~50 for Subdivs. 22–24 101 64 42 6 112
2002 IIIa: managed together with autumn spawners
22–24: if required, TAC not exceeding recent catches		 ~50 for Subdivs. 22–24 101 53 47 7 107
2003 Reduce F <80 101 40 36 2 78
2004 Separate management regime for this stockReduce F <92 91 42 24 7 77
2005 Separate management regime for this stockStatus quo F 95 120 44 38 7 89
2006 Separate management regime for this stockStatus quo F 95 1023/47.5* 42 36 11 89
2007 Separate management regime for this stockStatus quo F 99 693/49.5* 40 28 1 68
2008 Separate management regime for this stockReduce F by 20% towards F 0.1 71 51.73/45* 43 25 0 68
2009 Separate management regime for this stockReduce F to F = 0.25 < 32.8 37.73/27.2*        
2010 Separate management regime for this stockReduce F to F = 0.25 <39.8          
Weights in ‘000 t.1Catch in Subdivisions 22–24.2Including mixed clupeoid TAC and bycatch ceiling in small-mesh fishery.3 Human consumption in Division IIIa, not incuding industrial bycatch or mixed clupeoids, but including North Sea Autumn Spawner catch in fleet C.* separate TAC for SD 22–24.
Management
Management unit: Yes

Management Objectives

There are no explicit management objectives for this stock.
Management Advice

Management considerations

North Sea Autumn-Spawning and the Western Baltic Spring-Spawning herring stocks are exploited and managed simultaneously in Division IIIa. Hence, the management of the herring fisheries in Division IIIa influences both stocks.

Recruitment of Western Baltic herring has been reduced by 15–35% annually from 2004 onwards. The estimated strength of the 2008 year class is the lowest of the whole times series, and amounts to only a quarter of the average. There is no indication that recruitment would return to the previous level in the near future. The poor year classes have not yet fully contributed to the SSB but will increasingly do so in the near future. In this situation, there is no alternative to reduce F significantly to avoid a drastic decline of the SSB.

ICES has used the mean recruitment from 2003–2007 (year classes) for the short-term prediction which might be overly optimistic in the present situation.
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
Undefined Undefined Overfished NA  

In the absence of agreed reference points, the state of the stock cannot be evaluated. SSB has been stable in recent years but is expected to decline rapidly due to poor recruitment. Fishing mortality has been stable and is estimated at 0.37, well above the candidate for Fmsy. From 2004 onwards, recruitment has been declining and is now at a record-low.
Source of information
 
ICES. 2009. Report of the ICES Advisory Committee, 2009. ICES Advice, 2009.
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