Last updated on 12 July 2018
In 2012, this stock was considered a data-limited stock and advice was given based only on the development in the survey indices. The 2013 ICES assessment, the first analytical assessment for this stock since 2008, was a marked improvement over previous assessments. The assessment proposed during the benchmark in February 2013 (ICES 2013b) introduced a new model (Stochastic Multi-species (SMS) model with quarterly time-steps). Consistent with the past several years, the latest (2018) assessment (considered an update) includes three survey indices (IBTS Q1&3, HERAS), commercial catches (international landings, ages and length frequencies from catch sampling), annual maturity data from IBTS Q1 survey and natural mortalities from the multispecies model (ICES 2018). In 2013, to better match the sprat life-cycle, ICES changed the assessment year from January–December to July–June (ICES 2014a). This change was intended to facilitate more biologically coherent stock assessment.
The assessment shows high CVs for the catches but lower CVs for surveys. This may be due to low sampling effort in several years in spite of substantial catches taken. The CVs of F, SSB and recruitment are in general low (ICES 2018). The model converged and fitted the catches of the main ages caught in the main quarters (the periods with most samples) reasonably well. The CV of survey observations are in general lower. The assessment substantially overestimates large incoming yearclasses (ICES 2018). Retrospective patterns is strong (ICES 2018)
Discarding that occured in the years prior to the EU landing obligation (2015) was unquantified and thus cannot be included in stock assessments (ICES 2015a, 2015b). Discards of sprat since 2016 are assumed to be negligible (ICES 2018).
Stock assessment advice under the MSY escapement and Fcap strategy (see "Scientific Advice" section below) requires post-fishery predictions of spawning stock biomass (SSB). The sprat stock in the North Sea is dominated by young fish; and stock size is driven primarily by the recruiting year class. Thus, the fishery in a given year will be dependent on that year’s incoming year class (ICES 2015b). Unknown abundance and maturity rates for a high proportion of recruits regularly contribute to uncertainty in overall recruitment estimates and SSB predictions. High recruitments and SSB estimated in recent years have been revised downward in subsequent assessments (ICES 2016) (ICES 2017) (ICES 2018).
This fishery is under the mandates of the Common Fisheries Policy (CFP), which require management of the fishery’ ecosystem effects. In the North Sea, the key predators consuming sprats are included in the stock assessment, which uses Stochastic Multi-species (SMS) methodology to estimate sprat consumption for each predatory fish stock, and likewise for seabirds (ICES 2015b). These estimates are used as model inputs to derive stock assessment reference points and corresponding advice. By Marine Stewardship Council (MSC) assessment standards, this approach is considered to qualify as a “partial strategy” to prevent serious or irreversible harm to ecosystem structure and function (Rice et al. 2017). However, there is a related condition (see "ETP Species" section below). Meanwhile, stock assessments historically have not attempted to measure impacts of changes in zooplankton communities and consequent changes in food densities for sprats (i.e. bottom up effects); and ICES has recommended that there may be value in exploring this dynamic in future assessments (ICES 2015b).
Last updated on 12 July 2018
ICES utilizes particular strategies for short-lived fish stocks, for which future stock size is very dependent on incoming recruitments, which in turn are often the main or only component of the fishable stock (ICES 2014c). Their typical approach for these cases is aimed at achieving target escapement, MSY Bescapement, the amount of biomass left to spawn. For particularly sensitive species, recruitment often cannot be reliably estimated until very close to the time of the fishery; and to address this ICES has prescribed an adaptive framework, where a preliminary and very conservative TAC is first set, and then adjusted (typically much higher) following a later assessment of the stock size. In cases where recruitment information is poor, as for North Sea sprat, ICES has found an additional measure - an upper constraint to the escapement strategy derived fishing mortality (termed "Fcap") - necessary to guard against very high exploitation. Based on evaluations made in late 2013, ICES determined this necessary to ensure precautionary exploitation of the North Sea sprat stock, and set an intitial Fcap at 1.2 (ICES 2014a). In 2015, the use of new natural mortalities in the assessment resulted in the long-term geometric mean of recruitment being revised downwards. This implied also reducing the target fishing mortality (Fcap) from 1.2 to 0.7 (ICES 2015a).
ICES’ advice applies for the assessment year (1 July – 30 June), while management total allowable catch (TAC) has followed the calendar year (but note recent developments in this regard - see “Manager’s s Decisions” below). ICES has previously provided guidance for within-year adjustments to the TAC (ICES 2014a, 2016a). In 2017, ICES moved to an accelerated release of their advice (from June 30 to April) (ICES 2017) so that TAC adjustments could be made in advance of fishing (Rice et al. 2017). Based on the MSY approach, ICES advises that catches of sprat for the 2018-19 period should be no more than 177,545 tonnes (ICES 2018).
ICES’ additional recommendations for this fishery are: a) A management plan needs to be developed (ICES 2016b); b) Bycatch allocation must be monitored and management measures should consider sprat in other areas (ICES, 2012b, 2015b, 2016b); c) Management measures that address the bycatch of juvenile herring should be revisited and management of this stock should consider management advice given for herring in Subarea IV, Division VIId, and Division IIIa (ICES 2015b, 2016b); d) Given the importance of sprat as a forage fish, multispecies considerations should be made. ICES has been taking steps to gradually start providing multispecies advice on fisheries for some ecosystem (ICES 2013c; ICES 2017b). A final note in the 2017 advice (ICES 2017) cautions that the catch of sprat under quotas for other species (e.g. herring) (resulting from quota transfers allowed under the EU landing obligation) may result in overexploitation of North Sea sprat. To account for this risk, ICES advises that any transfers under this regulation should be accounted for in the set TAC.
European sprat in North Sea stock was benchmarked in 2013 (ICES 2013) (ICES 2013b), and reference points defined (ICES 2014a). Current reference points for this stock are as follows:
|MSY Bescapement||142,000 t||=Bpa in conjuntion with Fcap|
|Fcap(*)||0.7||based on the Bescapement strategy, with an additional constraint on fishing mortality (ICES 2015a)|
|Blim||90,000 t||set to ensure years of good recruitment occurred when SSB was above Blim, and years of poor recruitment occurred only when SSB was below Blim|
|Bpa||142,000 t||“=Blim × exp (σ × 1.645), with σ = 0.28 estimated from assessment uncertainty in the terminal year (ICES, 2013).”|
(*) The MSY proxy Fishing mortality reference point was revised in 2014 and then 2015.
The stock will be benchmarked again in 2018 (ICES 2018).
Last updated on 12 July 2018
The 2018 stock assessment (ICES 2018) finds the stock in good condition. Sprat stock size largely depends on recruitment year classes, resulting in high inter-annual variations in spawning stock biomass (SSB) along the historical series (ICES 2016b). Owing to a series of below average recruitments, estimated SSB showed a decreasing trend from 2010 to 2012, when it reached the biomass limit reference point (Blim) (ICES 2018). SSB has been above MSY Bescapement since 2013, and it is estimated to have increased from