Habitat and Biology
Depth zone: Shelf (50 m - 200 m). Vertical distribution: Demersal/Benthic.
Cod is the main predator on sprat and herring, and given the recent increase of the eastern Baltic cod stock the natural mortality of the pelagic stocks is likely to be affected. However, as the adult sprat and herring predate on cod eggs and larvae, an increased predation on clupeids can also have a positive effect on cod recruitment. At present, there is limited geographical overlap between cod and the pelagic stocks during parts of the year. Consistent with declining availability of sprat and herring and an increasing cod stock in the current main distribution area of cod (Subdivision 25), the mean weight of larger cod has sharply declined in this area in recent years.Environmental influence on the stock
Recruitment is strongly driven by hydrological factors. At present, successful reproduction of the eastern Baltic cod occurs only in the Bornholm Basin (Subdivision 25). The distribution of cod is currently mainly confined to Subdivision 25 and to a lesser degree Subdivision 26, with very low abundance in northern areas (Subdivisions 27–
Jurisdictional distribution: Shared between nations
Considered a single stock: Yes
The fisheries for cod in the eastern Baltic have very little bycatch of other species.
Effects of the fisheries on the ecosystem
||Total catch (2011) is 54.2 kt, where 93% are landings (20% by gillnetters, 80% by trawlers) and 7% discards.
Because sprat and herring are the major prey for cod, the cod fishery can indirectly affect the sprat and herring stocks by changing predation mortality on these species. Furthermore, the fishery for sprat and herring in the distribution area of cod can influence the available food base for cod.
ICES advises on the basis of the EU management plan (EC 1098/2007
) that landings in 2013 should be 65 900 tonnes.
Overall Assessment Results
|Figure 220.127.116.11 Cod in Subdivisions 25–32. Summary of stock assessment (weights in ‘000 tonnes). Predicted values are shaded. Top right: SSB and F for the time-series used in the assessment. |
Assessment ModelQuality consideration
The SBB has been consistently overestimated in the last three years. The longest survey series has a break in 2001 when the survey design was altered. The commercial fleet, on which the cpue index has been based, was subjected to a new quota regulation system prohibiting high-grading and aimed at improving selectivity of gears. Substantial underreporting of catches occurred in 1993–1996 and 2000–2007. In this situation, ICES has chosen to include estimates of non-reported landings in the assessment. These estimates are likely to be lower than the actual non-reported landings. Ageing problems are a concern for the quality of the assessment. Collection of cod stomach contents data would improve the basis for application of multispecies stock assessment models. Data are needed to quantify the amount of mixing of cod by age groups between the eastern and western Baltic. Tagging experiments or/and genetic analysis could provide such data.
|Figure 18.104.22.168 Cod in Subdivisions 25–32. Historical assessment results (final-year recruitment estimates included). |
||Age-based analytical (XSA).
||Two surveys (BITS Q1&4), five indices (two BITS Q1 of ages 3–6 backshifted, two BITS Q1_of age 2, and one commercial index (Den_Trawl_>90 mm)).
|Discards and bycatch
||Discards included in the assessment.
||Last benchmarked in 2009. The next benchmarking for this stock is scheduled for 2013.
|Working group report
Management unit: YesManagement plans
A multi-annual plan for cod in the Baltic Sea has been agreed by the EU in 2007 ((EC) No. 1098/2007
). ICES has evaluated the management plan in 2009 and considers it to be in accordance with the precautionary approach. The target F in the management plan is equal to the recent estimate of FMSY
for this stock. The management plan is currently under revision.
Biological State and Trend
|Figure 22.214.171.124 |
ICES considers the present SSB to be above any candidate precautionary biomass reference points. The SSB has increased in recent years and is estimated to be 263 000 tonnes at the start of 2012. Fishing mortality in 2008–2011 was estimated to be the lowest in the series. The abundance of the 2006, 2007, 2008, and 2009 year classes (at age 2) is above the average of the last 20 years.
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. Cod in Subdivisions 25–32. Report of the ICES Advisory Committee, 2012. ICES Advice, May 2012. http://www.ices.dk/committe/acom/comwork/report/2012/2012/cod-2532.pdf