Habitat and Biology
Depth zone: Shelf (50 m - 200 m). Vertical distribution: Pelagic.
Sprat in the North Sea is short-lived with high natural mortality and the catch is dominated by young fish. The stock size is mostly driven by the recruiting year class. Thus, the fishery in a given year is dependent on that year’s incoming year class.Environmental influence on the stock
The zooplankton community structure that is sustaining the sprat stocks appears to be changing, and there has been a long-term decrease in total zooplankton abundance in the northern North Sea (Reid et al., 2003; Beaugrand, 2003; ICES, 2006a). The implications of the environmental change for sprat are unknown.
Jurisdictional distribution: National
Considered a single stock: Yes
The majority of the sprat landings are taken in the Danish small-meshed trawl fishery. In this fishery there is about 10% bycatch of herring. The Norwegian sprat fishery is mainly carried out by purse seiners. Landings are used for reduction for fish meal and fish oil. Most sprat catches are taken in an a small meshed fishery where catches are limited by herring bycatch restrictions. Bycatches of herring are practically unavoidable except in years with high sprat abundance or low herring recruitment. Given the recent increase in the North Sea Autumn Spawning herring stock, the sprat fishery in has been increasingly limited by the by-catch limits.Effects of the fisheries on the ecosystem
Sprat is an important prey species in the North Sea ecosystem. The effects of the sprat fishery on other fish species, marine mammals and seabirds are at present unknown.
Based on the ICES approach for data limited stocks, ICES advises that catches should not be more than 134 000 tonnes (catches of 2011).
This is the first year that ICES is providing quantitative advice for data limited stocks (see Quality considerations).
Overall Assessment Results
|Figure 18.104.22.168 Sprat in Subarea IV (North Sea). ICES estimates of landings (in ‘000 tonnes), relative biomass estimate from the HERAS survey, and relative abundance estimate from the IBTS survey (* marked estimates are preliminary). |
Assessment ModelQuality consideration
Both the IBTS and the HERAS acoustic survey are currently considered to potentially provide basis for an abundance index. The sampling intensity in Subarea IV has improved in 2011, but is still below the reference level of 0.5 sample per kt in Division IVc where the majority of the fisheries takes place. A reanalysis of the data during the 2012/13 benchmark should further reveal data needs.
The methods applied to derive quantitative advice for data limited stocks are expected to evolve as they are further developed and validated. Scientific basis
||There is currently only an explorative assessment for this stock.
||3 survey indices (IBTS Q1&3, HERAS)
|Discards and bycatch
||Bycatches from the Danish sprat fishery
||For this short-lived stock, in year advice is given A benchmark for this stock is planned for 2013.
Management unit: YesManagement plans
No specific management objectives are known to ICES.
Biological State and Trend
Exploitation rate: Unknown
Abundance level: Increasing
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. Sprat in Subarea IV (North Sea). Report of the ICES Advisory Committee, 2012. ICES Advice 2012. http://www.ices.dk/committe/acom/comwork/report/2012/2012/spr-nsea.pdf