Habitat and Biology
Depth zone: Shelf (50 m - 200 m). Vertical distribution: Demersal/Benthic.
Plaice is a bottom dwelling species, mainly feeding on annelids and molluscs. Plaice aggregate at spawning grounds in the first quarter of the year. The condition factor for plaice is highest in summer/autumn on the more dispersed feeding grounds. These feeding grounds are generally located more northerly than the spawning grounds.Environmental influence on the stock
Juvenile plaice have been distributed more offshore in recent years. This could be linked to environmental changes in the productivity or changes in the temperature of the southern North Sea, but these links have not been shown conclusively. The distribution shift of plaice increased the bycatch of small plaice further offshore.
Jurisdictional distribution: Shared between nations
Considered a single stock: Yes
Plaice is predominantly caught by beam trawlers in the central part of the North Sea with a minimum mesh size of 100–120 mm depending on area. A mixed fishery with sole in the southern North Sea takes place with a minimum mesh size of 80 mm. This mesh size catches plaice under the minimum landing size of 27 cm, which causes high discard rates (in the range of 50% by weight). The discard ratio in the catch has declined in recent years.
Effects of the fisheries on the ecosystem
||Total catch (2011) = 108.523 t, where 63% are landings (60% beam trawl, 36% otter trawl, and 5% other gears), 37% are discards and <1% industrial bycatch.
The mixed plaice and sole fishery is dominated by bottom trawls, with bycatch of both commercial and non-commercial species and a physical impact on the seabed. Bottom trawling impacts biomass, production, and species richness. For plaice, the size selectivity may lead to a shift in the age and size at maturation, which means individuals start spawning earlier.
ICES advises on the basis of the EU management plan (Council Regulation No. 676/2007) that landings of plaice in Subarea IV in 2013 should be no more than 97 070 t. The implementation of stage two of the plan (as stipulated in article 5 of the EC regulation) is not yet defined.
Overall Assessment Results
|Figure 18.104.22.168 Plaice in Subarea IV (North Sea). Summary of stock assessment (weights in ‘000 tonnes). Top right: SSB and F for the time series used in the assessment. |
Assessment ModelScientific basis
||Age-based analytical assessment (XSA).
||Three survey indices (BTS-Tridens, BTS-Isis, SNS).
|Discards and bycatch
||Included in the assessment.
||This stock was benchmarked in 2009 (WKFLAT).
|Working group report
Management unit: YesManagement plans
The EU management plan for North Sea plaice and sole (Council Regulation (EC) No. 676/2007, see Appendix 6.4.7). An evaluation of the plan (ICES, 2010) concluded that the management plan is precautionary.
Biological State and Trend
Exploitation rate: Below target
Abundance level: Above target
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. Plaice in Subarea IV (North Sea). Report of the ICES Advisory Committee, 2012. ICES Advice, WKNSSK 2012. http://www.ices.dk/committe/acom/comwork/report/2012/2012/ple-nsea.pdf