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Herring - Bothnian Sea
Marine Resource  Fact Sheet
ICES Advice 2012
Herring - Bothnian Sea
Fact Sheet Citation  
Herring in Subdivision 30 (Bothnian Sea)
Owned byInternational Council for the Exploration of the Sea (ICES) – More
Related observationsLocate in inventorydisplay tree map
 
Species:
FAO Names: en - Atlantic herring, fr - Hareng de l'Atlantique, es - Arenque del Atlántico, ru - Сельдь атлантическая
Geographic extent of Herring - Bothnian Sea
Main Descriptors
Considered a single stock: Yes        Spatial Scale: Sub-Regional
Management unit: No        Reference year: 2012
 
 
Biological State and Trend
State & Trend Descriptors
PartnerFIRMS
Exploitation rateAppropriateModerate fishing mortality
Abundance levelAbove triggerIntermediate abundance
Figure 8.4.6.2

The spawning-stock biomass tripled between the mid-1980s and mid-1990s and thereafter decreased by 40% until 1999. In the 2000s SSB remained high and has increased further after 2008. There is, however, great uncertainty around the estimates. Since the beginning of the time-series, the most likely estimates of fishing mortality have been below FMSY and have exceeded FMSY only in 1997 and 1999. Prior to 1994, recruitment was stable and low and has continued to remain stable over the past 20 years, but at a slightly higher average value than previously. The three year classes 2002, 2006, and 2008 are the most abundant in recent years. Landings in 2011 were the highest recorded over the time-series.
Habitat and Biology
Depth zone: Shelf (50 m - 200 m).   Vertical distribution: Pelagic.  


The growing grey seal population in the Bothnian Sea has resulted in increased predation on herring.

Environmental influence on the stock

The body weight of herring in the Bothnian Sea has declined over the last 20 years. The decrease in weight-at-age may be the result of a combination of density-dependent effects and a decrease in zooplankton prey.
Geographical Distribution
Jurisdictional distribution: Shared between nations

Water Area Overview
Spatial Scale: Sub-Regional


Baltic Sea
Geo References
Resource Structure
Considered a single stock: Yes
Exploitation
 

The fisheries


On average, 95% of the total catch is taken by the trawl fishery; the trapnet fishery is of minor importance. The small-scale herring gillnet fishery has a declining importance in coastal areas in Sweden. In the trawl fishery, larger and more effective trawls have been introduced in the 1990s. Sprat bycatches in herring fisheries are low in ICES Subdivision 30.
Catch distribution Total landings (2011) are 78.5 kt (4% trapnets, 95% trawls, and 1% gillnets). Discards are negligible.



Effects of the fisheries on the ecosystem

With a low fishing mortality and high stock size, the effect of the fisheries on the ecosystem is probably not significant from a trophic point of view.
Assessment
 
Scientific Advice

ICES advises on the basis of the MSY framework that catches in 2013 should be no more than 97 000 tonnes.
Overall Assessment Results
Figure 8.4.6.2 Herring in Subdivision 30, Bothnian Sea. Historical performance of the assessment. A new assessment model and revision of input data was considered in 2012.
Assessment Model

Quality consideration


In contrast to the XSA model used previously, the retrospective patterns on SSB and F from the state–space model (SAM) do not show any trends. It is anticipated that extending the acoustic survey time-series and reconstructing commercial tuning fleets will improve the quality of the assessment.
Figure 8.4.6.2 Herring in Subdivision 30, Bothnian Sea. Historical performance of the assessment. A new assessment model and revision of input data was considered in 2012.

Scientific basis



Assessment type State–space model (SAM).
Input data Acoustic survey indices from 2007 to 2011, and one commercial cpue series, Finnish trapnet fleet.
Discards and bycatch Negligible discards. Small bycatches of sprat/mixed landings of herring and sprat, mainly from southern parts of the Bothnian Sea.
Indicator The trends in acoustic abundance and biomass estimates support the assessment results.
Other information Benchmark for the Subdivision 30 herring stock was carried out in 2012.
Working group report WGBFAS
Management
Management unit: No


Management plans


No specific management objectives are known to ICES.
Source of information
 

The above excerpts are from the first two pages of the ICES advice, the supporting information to this advice can be read in full at the following reference:
ICES. Herring in Subdivision 30 (Bothnian Sea). Report of the ICES Advisory Committee, 2012. ICES Advice, May 2012. Click to openhttp://www.ices.dk/committe/acom/comwork/report/2012/2012/Her-30.pdf
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