Français
Herring - Bothnian Sea, 2006
Marine Resource  Fact Sheet
SearchSavePrint
Stock status report
Herring - Bothnian Sea, 2006
Herring in Sub-division 30, Bothnian Sea
Fact Sheet Citation  
Owned byInternational Council for the Exploration of the Sea (ICES)   more>>
Related observationsLocate in inventorydisplay tree map
 
Species:
Clupea harengus
Species thumbnail
Fao Names :  en - Atlantic herring, fr - Hareng de l'Atlantique, es - Arenque del Atlántico
Distribution of Herring - Bothnian Sea
 Map legend

Area Details Advanced search
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: National

Water Area Overview
Spatial Scale: Sub-Regional

Geo References
Resource Structure
Considered a single stock: Yes
Exploitation
 

Factors affecting the fisheries and the stock


Most of the Baltic herring catch in the Bothnian Sea is taken in a targeted herring fishery. During autumn and early winter there are mixed catches of Bothnian Sea herring and sprat, but these are minimal.

The EU has given Finland and Sweden a dispensation up to the end of the year 2011 to utilize fish with higher contents of dioxin and PCB than the limit. During the 1990s, no decrease has been observed in the dioxin contents in Baltic herring from the Bothnian Sea. With the present exploitation rate and high recruitment, the amount of older herring in the stock will increase and thus also the dioxin content of herring.

Changes in fishing technology and fishing patterns


On average, 95% of the total catch is taken by the trawl fishery. The trapnet fishery is of minor importance. In the trawl fishery, larger and more effective trawls have been introduced in the 1990s.

The environment


Herring weight-at-age has shown a declining trend since the late 1980s, possibly caused by limited food supply due to changes in zooplankton species composition and density-related effects following very good recruitment.
Assessment
 
Assessment Model
Assessment Model Entry
Data

Scientific basis


Data and methods


The assessment is based on catch data with revised ageing for the years 2002–2006 in Finnish samples, and on two commercial cpue series.

As the reported fishing effort data (trawling hours) is not considered to reflect fishing mortalities correctly, correction coefficients have been used for trawl fishing effort data in 1980–2006.

Uncertainties in assessment and forecast


No fishery-independent information is available. The present assessment uses commercial cpue series, which are known to be unreliable for pelagic schooling species in principle. A fishery-independent acoustic survey was initiated in 2007, but it will take at least 5 years before this series can be used in the assessment. Once included, the perception of the stock trends might change drastically.

There are uncertainties in the estimates of SSB and F in recent years as visible in the retrospective pattern, showing an underestimation of SSB and overestimation of F.

Variation in environmental conditions affects growth rate and natural mortality, but such variation cannot be quantified and all calculations are therefore based on a constant natural mortality (0.2) for all periods and age groups. Predation by grey seals was analysed and found to be insignificant for the current assessment. However, due to the rapid increase in the grey seal population, this conclusion should be re-evaluated in future assessments.
Overall Assessment Results

Comparison with previous assessment and advice


The current assessment has revised the estimated SSB in 2005 upwards by about 8%. The estimate of F has similarly been revised downwards by about 6%. The basis for the advice is unchanged.
Graphs 
Graphs 
Graphs 
Graphs 


Figure 8.4.6.1 Herring in Subdivision 30, Bothnian Sea. Landings, fishing mortality, recruitment, and SSB.
Graphs 
Graphs 
Graphs 


Figure 8.4.6.2 Herring in Subdivision 30, Bothnian Sea. Stock and recruitment, yield and SSB per recruit.
Graphs 


Figure 8.4.6.3 Herring in Subdivision 30, Bothnian Sea. Stock and recruitment. Historical performance of the assessments.

Landing table


Table 8.4.6.1 Herring in SD 30. Catches in Subdivision 30 (tonnes).
Landing table
Year Finland Sweden Total
1971 24284 5100 29384
1972 24027 5700 29727
1973 20027 6944 26971
1974 17597 6321 23918
1975 13567 6000 19567
1976 19315 4455 23770
1977 22694 3610 26304
1978 22215 2890 25105
1979 17459 1590 19049
1980 18758 1392 20150
1981 12410 1290 13700
1982 16117 1730 17847
1983 16104 2397 18501
1984 23228 2401 25629
1985 24235 1885 26120
1986 23988 2501 26489
1987 22615 1905 24520
1988 24478 3172 27650
1989 25453 3205 28658
1990 28815 2467 31282
1991 23219 3000 26219
1992 35610 3700 39310
1993 36600 3579 40179
1994 53860 2520 56380
1995 58806 2280 61086
1996 54372 1737 56109
1997 63532 1995 65527
1998 54115 2777 56892
1999 60483 1862 62345
2000 54886 1374 56261
2001 52987 1997 54984
2002 46315 3903 50218
2003 45932 3707 49638
2004 50236 5214 55450
2005 55422 2 520 57 942
2006 66962* 1403 68365
* preliminary. - -

Table 8.4.6.2 Herring in Subdivision 30, Bothnian Sea.
Stock summary
Year Recruitment SSB Landings Mean F
- Age 1 - - Ages 3-7
  thousands tonnes tonnes  
1973 2062493 140712 22531 0.1632
1974 2552283 148305 20294 0.1438
1975 1837596 153207 16264 0.1027
1976 4049208 151128 22012 0.1415
1977 1451782 141034 26304 0.1995
1978 772094 147300 25105 0.2003
1979 501629 135170 19049 0.1516
1980 1489584 116346 20150 0.1837
1981 1428466 112313 13700 0.1385
1982 2431712 99048 17847 0.2018
1983 3426490 108457 18501 0.1607
1984 4713825 127037 25629 0.2098
1985 4136190 154798 26120 0.1865
1986 2400115 174544 26489 0.1435
1987 4113174 218042 24520 0.1249
1988 1772673 223118 27650 0.1128
1989 6905145 301559 28658 0.0937
1990 7222044 358416 31282 0.0824
1991 4277512 389537 26219 0.0724
1992 4923237 391670 39310 0.1019
1993 5938359 369141 40179 0.0922
1994 4185464 424424 56380 0.1486
1995 5582034 358160 61086 0.1793
1996 4019870 367587 56109 0.1704
1997 3852663 305248 65527 0.2366
1998 6622587 291232 56892 0.2046
1999 3800636 267089 62345 0.2319
2000 4492758 304641 56261 0.2136
2001 4655740 264575 54984 0.1907
2002 6966648 303355 50218 0.1404
2003 16311979 313226 49638 0.1457
2004 2195229 331068 55450 0.1562
2005 3478722 366874 57941 0.1496
2006 4752133 320866 68635 0.1692
2007 4732030 312000    
Average 4115832 246448 37332 0.1572
Reference Point
 
Reference points(unchanged since 2000)

Yield and spawning biomass per Recruit
F-reference points
Reference points
  Fish Mort Yield/R SSB/R
  Ages 3–7    
Average last 3 years 0.158 0.009 0.049
Fmax 0.370 0.010 0.026
F0.1 0.141 0.009 0.053
Fmed 0.067 0.007 0.076
Projection

Short-term implications


Outlook for 2008


Basis: F(2007) = Fsq = 0,16; SSB(2007) = 312 kt; Landings (2007) = 56 kt.Outlook for 2008Weights in ‘000 t. Shaded scenarios are not considered consistent with the precautionary approach.
1) SSB 2009 relative to SSB 2008.
2) TAC 2008 relative to TAC 2007.
Scientific Advice

Single-stock exploitation boundaries


Exploitation boundaries in relation to precautionary considerations


Fishing below Fpa in 2008 corresponds to landings of less than 67 300 t.

Management considerations


Catches from this stock comprise the major fraction of the TAC set for the Management Unit, consisting of Subdivisions 30 and 31.

Most herring is taken in trawl fisheries. The sprat bycatches in herring fisheries are low in ICES Subdivisions 30 and 31.

SSB is presently at a high level, mostly due to the strong 2002 year class.

Ecosystem considerations


Stock trends in Bothnian Sea herring have since the 1990s been driven mainly by good recruitment and by lower fishing mortality in the most recent years. In addition to higher recruitment, an important ecosystem-related aspect of Baltic herring in the Bothnian Sea is the decrease in growth during the 1990s. This may be related to the decrease in the abundance of the copepod Pseudocalanus sp., one of the most important food items of Baltic herring, and an increase of herring density.

With the present low exploitation level it is expected that the dioxin concentration in the fish caught will increase, as the amount of older herring (which have higher accumulated amounts of dioxin) will increase in the stock and in the catch.
Management
Considered a management unit: Yes

Management Objectives

There are no explicit management objectives for this stock. Herring management for Subdivisions 30 and 31 is combined.

Catch and TACs
Catch and TACsWeights in ‘000 t.
1Catch at F01.
2TAC for the Areas 29N, 30, and 31 (IBSFC Management Unit 3), and from 2005 for Areas 30 and 31.
Biological State and Trend
Exploitation rate:   Harvested sustainably                   
Abundance level:   Full reproductive capacity    

State of the stock
Based on the most recent estimates of SSB and fishing mortality, ICES classifies the stock as having full reproductive capacity and as being harvested sustainably. The spawning stock biomass has been well above Bpa since the late 1980s. The fishing mortality decreased since 1999 and has been below Fpa since 2001, hovering around F=0.15.

Recruitment has been high since 1989 and the 2002 year class appears exceptional. The 2003 year class is estimated to be among the lowest since 1988, year class 2004 is below the average, and year class 2005 is average.
Source of information
 

Report of the Baltic Fisheries Assessment Working Group. ICES Headquarters, 17–26 April 2007 (ICES CM 2007/ACFM:15).
ICES Click to open.
powered by FIGIS   © FAO, 2000-2008
crawl