FIRMS - Marine Resource Fact Sheet - Spring Spawning Herring

Spring Spawning Herring - Skagerrak and Kattegat, 2006

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Stock status report

Spring Spawning Herring - Skagerrak and Kattegat, 2006

Herring in Sub-divisions 22-24 and Division IIIa (spring spawners)

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International Council for the Exploration of the Sea (ICES) more>>

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Species:

Clupea harengus

Fao Names : en - Atlantic herring, fr - Hareng de l'Atlantique, es - Arenque del Atlántico

Distribution of Spring Spawning Herring - Skagerrak and Kattegat

Map legend Area Details

Main Descriptors
Considered a single stock: Yes Spatial Scale: Sub-Regional Considered a management unit: Yes

Table of Contents

Habitat and Biology - Water Area Overview - Geographical Distribution - Exploitation - Assessment - Management - Biological State and Trend - Source of information

Habitat and Biology

Depth zone: Shelf 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 having been 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 with the incentive to decrease misreporting for the Norwegian part of the fishery. Working group estimates may be underestimating the problem since not all countries supply this information to ICES.

The quota for the C-fleet and the bycatch quota for the D-fleet are set for the NSAS and the WBSS stocks together. The implication for the outtake of NSAS must be taken into account when setting fleet-wise quotas for these stocks.

Changes in fishing technology and fishing patterns

Since 2001, the fishery behavior has changed in the German fleet. In former years, the main catch of herring was taken in the passive gears, bottom-set gillnets, and trapnets. Recently the landings by trawl have reached a level of more than 50% of the total landings (2003: 63%, 2004: 52%, 2005: 57%, and 2006: 64%). This change is due to requirements from a new fish factory on the Rügen Island.

The environment

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.

Assessment

Assessment Model

Assessment Model Entry

Data

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 1991–2006. An analytical assessment is based on catch data and acoustic and trawl survey results.

Development of stock identification methods using combinations of genetics and otolith analyses continues but, in order to improve the assessment, annual acoustic surveys covering the entire stock should be implemented as soon as possible.

Uncertainties in assessment and forecast

There is no firm basis for predicting 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.

The assessment is uncertain, and based on diverging signals from tuning fleets and surveys.

Information from the fishing industry

The fishing industries confirm that substantial area misreporting occurs from the North Sea to the Skagerrak and this has to some extent been taken into account in the assessment.

Overall Assessment Results

Exploitation boundaries in relation to high long-term yield, low risk of depletion of production potential and considering ecosystem effects

If target reference points are to be established, F_0.1 would be associated with high long-term yields and low risk of reduced reproductive capacity. The current fishing mortality exceeds the fishing mortality associated with F_0.1.

Comparison with previous assessment and advice

Compared to last year’s assessment, the change in the estimate is +21% for the fishing mortality in 2005 and -6% for the SSB in 2005 (Figure 6.4.17.3). This year the advice is a reduction in F towards F _0.1.

Graphs

Figure 6.4.17.1 Herring in Subdivisions 22–24 and Division IIIa (spring spawners). Landings, fishing mortality, recruitment, and SSB.

Graphs

Figure 6.4.17.2 Herring in Subdivisions 22–24 and Division IIIa (spring spawners). Stock recruitment, yield and SSB per recruit, precautionary approach.

Graphs

Figure 6.4.17.3 Herring in Subdivisions 22–24 and Division IIIa (spring spawners). Historical performance of the assessments. Note: some historical assessments may have been indicative of trends only.

Landing table

Table 6.4.17.1 Herring in Subdivisions 22–24 and Division IIIa (spring spawners).

Landing table

Table 6.4.17.2 Herring in Subdivisions 22–24 and Division IIIa (spring spawners).
Stock summary

Year	Recruitment	SSB	Landings	Mean F
-	Age 0	-	-	Ages 3–6
	thousands	tonnes	tonnes
1991	4948600	291885	191573	0.3875
1992	3608410	300193	194411	0.5183
1993	3056560	275864	185010	0.5850
1994	6107580	216065	172438	0.7507
1995	3999770	169325	150831	0.5564
1996	4339120	124469	121266	0.7704
1997	3863760	137152	115588	0.5713
1998	5560200	111615	107032	0.5555
1999	6257570	117525	97240	0.4190
2000	3328150	128178	109914	0.5312
2001	4613680	147878	105803	0.5239
2002	2812740	182038	106191	0.5701
2003	4325300	141617	78309	0.4482
2004	2900010	158180	76815	0.4440
2005	2054450	155248	88406	0.4940
2006	1313450	184516	88931	0.5220
2007	3521756*
Average	3918300	177609	124360	0.5405

* Geometric mean 2000–2004.

Reference Point

There are no precautionary approach reference points for this stock.

Yield and spawning biomass per Recruit F-reference points:
Reference points

	Fish Mort	Yield/R	SSB/R
	Ages 3–6
Average last 3 years	0.487	0.027	0.047
F_max	0.528	0.027	0.043
F_0.1	0.219	0.024	0.100
F_med	0.556	0.027	0.040

Projection

Short-term implications

Outlook for 2008

Basis: F(2007 = F_sq = 0.522; SSB(2007) = 154; catch (2007) = 90, SSB(2008) = 135.
Landings are for Division IIIa spring-spawning herring and western Baltic (Subdivisions 22–24) combined, see further in Section 6.4.8 on North Sea herring (autumn spawners).Outlook for 2008 Weights in ‘000 t.

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. Likewise, the 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. The basis for the split of the WBSS herring catch by area and of the catch in Division IIIa by stock was the average ratios between the catches in 2004–2006. The current relevant fleet definitions are:

North Sea

Fleet A: Directed herring fisheries with purse-seiners and trawlers. Bycatches in industrial fisheries by Norway are included.
Fleet B: Herring taken as bycatch under EU regulations.

Division IIIa

Fleet C: Directed herring fisheries with purse-seiners and trawlers.
Fleet D: Bycatches of herring caught in the small-mesh fisheries.

Subdivisions 22–24

Fleet F: All herring fisheries in Subdivisions 22–24.

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).

Outlook for 2008

The catch option for 2008 is based on the share by fleet and stock composition in catches given as a mean for 2004 to 2006. Predicted catches of WBSS and NSAS herring by fleet in Division IIIa are based on recent patterns of 1) ratio of WBSS catches taken by each fleet, and 2) proportion of the two stocks in catches of the different fleets.

The ratio by fleet and stock composition is given in the following tables A and B, respectively:

Text table A showing the 2004 to 2006 average share of the total catch in t of WBSS by each fleet.Outlook for 2008 *A constant catch of 8400 t of WBSS caught in Subarea IV are accounted for in the calculations

Text table B showing the 2004 to 2006 average proportion of WBSS in catches by fleet Outlook for 2008
Short-term predictions indicate a catch in 2007 of 89 900 t with status quo fishing mortality (F_sq). The projected stock composition was assumed to equal the 2004–2006 average of the NSAS and WBSS in each of the C and D fleets (in Division IIIa) and a 2004–2005 average catch of 8400 t of WBSS taken in Subarea IV.

The table below provides the 2008 catch options for the Western Baltic spring spawners in Division IIIa, in SD 22–24, and in Subarea IV, along with several other options between 40 000 and 90 000 t.Outlook for 2008 Weights in ‘000 tonnes.
¹⁾ Relative to the TACs for 2007; Fleet C: 69 360 tonnes, Fleet D: 15 396 tonnes, Fleet F: 49 500 tonnes

For a quota of NSAS and total catch by the fleets in Division IIIa to be compatible with the advice for WBSS, the numbers derived as above, based on the largest advisable catch of WBSS, are upper bounds on the advisable catches of NSAS by the C- and D-fleets. Thus the resulting catch options were also used as constraints for short-term predictions for the NSAS herring.

Scientific Advice

Single-stock exploitation boundaries

Exploitation boundaries in relation to precautionary considerations

The recruitment has shown a declining trend in recent years and fishing mortality is estimated at a stable high level compared to other herring stocks. Continued exploitation at current fishing mortality levels is therefore likely to lead to a decline in the stock if not reduced.

Conclusion on exploitation boundaries

In the absence of a management plan and agreed target and precautionary reference points ICES advises to reduce fishing mortality towards F_0.1within 3 to 5 years. This would correspond to a 20% reduction of F and a corresponding TAC of less than 71 000 t in 2008.

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. The advisory emphasis on one or the other stock will vary between periods and depends on their relative status.

The assessment indicates a recent increase in SSB to 185 000 t in 2006, likely driven by the quite large 2003 year class coming through. The short-term projection with recent catch levels show a decline in SSB which indicates that fishing mortality should be reduced. Catches based on F_0.1quickly re-establish the SSB to above-average values at the cost of high reductions in yield. Applying an incremental approach towards F_0.1 (as a proxy for maximum sustainable yield) may be achieved on a longer-term basis by successive 20% F reductions, provided recruitment levels are not further reduced.

This herring stock displayed very low recruitment after 2003. The reduction is in line with recent developments in North Sea herring, with which Western Baltic herring shares the same environment at least for part of the year. At present, ICES cannot predict when and if recruitment would return to average and a geometric mean recruitment has therefore been used for the short-term prediction. However, given the recent experience with North Sea herring, it is not unlikely that the period with low recruitment continues. This would then imply that catches in the following years would have to be reduced even more in order to stabilise SSB.

Management

Considered a management unit: Yes

Management Objectives

There are no explicit management objectives for this stock.

Catch and TACs
Catch and TACsWeights in ‘000 t.
¹Catch in Subdivisions 22–24.
²Including mixed clupeoid TAC and bycatch ceiling in small-mesh fishery.
³ Human consumption not incuding industrial bycatch or mixed clupeoids.
* separate TAC for SD 22–24.

Biological State and Trend

Exploitation rate: Undefined
Abundance level: Undefined

There are no defined reference points for this stock. The assessment shows that the SBB has been stable over a number of years. Fishing mortality has also been stable for many years, but recruitment has declined since 2003.

Source of information

Report of the Herring Assessment Working Group for the Area South of 62°N, 13–22 March 2007 (ICES CM 2007/ACFM:11).

ICES