The ICES herring assessment working group (HAWG) met on an interactive virtual platform for nine days in March 2021 to assess the state of five herring stocks and three sprat stocks. HAWG also provided advice for eight sandeel stocks but reported on those, prior to this meeting, in Feb-ruary. The working group conducted update assessments for four of the five herring stocks. The assessment of the North Sea autumn spawning herring was postponed to an interbenchmark 8–10 June 2021 (IBPNSHerring 2021). An analytical assessment was performed for the combined North Sea and Division 3.a sprat, and data limited assessment (ICES category 3 and 5) were conducted for English Channel sprat (spr.27.7de) and sprat in the Celtic Sea (spr.27.67a-cf-k).

The North Sea autumn spawning herring (her.27.3a47d) assessment is postponed to the inter-benchmark in June 2021 and advice will follow in September 2021.

The Western Baltic spring-spawning herring (her.27.20-24) assessment was updated. The SSB and recruitment in 2020 are at record low levels. SSB is estimated to be around 58 400 tonnes which is below both Bpa and Blim. Recruitment has been low since 2006 and it has been further de-teriorating with time. Fishing mortality has decreased in 2018 to 0.19 and is now below FMSY (0.31). The stock has decreased consistently during the second half of the 2000s and given the con-tinued low recruitments, the stock is not able to recover above Blim unless a drastic reduction in fishing effort is applied.

The Celtic Sea autumn and winter spawning stock (her.27.irls) is estimated to be at a very low level. SSB is currently estimated to be at the lowest level in the time-series and has been below Blim (34 000 t) since 2016. Mean F(2–5 rings) was estimated at 0.023 in 2020, having decreased from the peak of 1.2 in 2018. Recruitment has been consistently below average since 2013.

The assessment of the combined stocks of herring in 6.aN and 6.aS/7.b, c (her.27.6a7bc) went through an interbenchmark procedure in 2019 and the advice is based on trends from an analytical assessment. SSB has decreased since 2003. SSB in 2020 is estimated to have increased from the 2019 level but remains at a very low level relative to the long term mean. Recruitment has been low with no strong cohorts in recent years. Fishing mortality has reduced since 2016 when catches have been limited to a scientific monitoring TAC but recovery of the stock is hampered by the very low recruit-ment.

Irish Sea autumn spawning herring (her.27.nirs) assessment shows an increase in SSB in 2020 to 27 500 tonnes which is the highest in the current time series. The stock has experienced large incoming year classes in recent years. Fishing mortality (F4–6) has been stable at 0.2 since 2013 and is below FMSY (0.266). Catches increased in 2020 in line with the increased TAC.

North Sea and 3.a sprat (spr.27.3a4) were combined into a single assessment unit during the 2018 benchmark. Perception of the status of the stock is dominated by the dynamics in Subarea 4 where most of the catches occur. Despite the fact that fishing mortality in the last years has fluctuated at high levels between 0.6–2.2, recruitments slightly but consistently above the aver- age during recent years have contributed to an increase in SSB well above MSY Bescapement. The estimates for 2021 show an SSB of 162 000 t which is above Bpa (125 000 t).

Catch advice for sprat in the English Channel (7.d, e) (spr.27.7de) was based on criteria for ICES category 3 stocks using the acoustic survey. The stock went through an interbenchmark in 2021 and a new basis for advice was recommended.

Advice is now provided using a constant harvest rate of 8.57% of the acoustic survey biomass. The new advice basis has led to a 100% increase in catch advice for 2022.

Catch advice for sprat in the Celtic Seas and West Of Scotland (spr.27.67a-cf-k) was given for 2022 and 2023 using the ICES category 5 based method where only landings data are available. The precautionary buffer was applied and a 20% decrease in catch is advised.

The HAWG reviewed the category 1 assessments performed on four sandeel stocks (SA 1r-3r, 4) and the category 3-6 assessments of four more sandeel stocks (SA 5r, 6, 7r, Div. 6a) and updated the related advice. Section 9 of this report contains the assessments of sandeel in Division 3.a and Subarea 4.

Standard issues such as benchmark planning, the quality and availability of data, estimating the amounts of discarded fish, availability of data through industry surveys and scientific advances particularly with respect to the use of genetics for stock discrimination were discussed.

All data and scripts used to perform the assessments and the forecast calculations are available at https://github.com/ICES-dk/wg_HAWG and accessible to anyone.