The main terms of reference for the The ICES Working Group for the Assessment of Demersal Stocks in the North Sea and Skagerrak (WGNSSK) were: to update, quality check and report relevant data for the working group, to update and audit the assessment and forecasts of the stocks, to produce a first draft of the advice on the fish stocks and to prepare planning for bench-marks in future years. Ecosystem changes have been analytically considered in the assessments for cod, haddock and whiting in the form of varying natural mortalities estimated by the ICES Working Group on Multi Species Assessment Methods (WGSAM).
Benchmarks in 2021/2022
Full benchmarks were conducted during 2022 for WGNSSK stocks. These were on haddock in Subarea 4, Division 6.a and Subdivision 20 and plaice in Subarea 4 and Subdivision 20. There is an inter-benchmark protocol (IBP) meeting planned during 2022, for sole in Division 7.d to in-clude a change to SAM settings allowing for variability in survey catchability over time.
State of the Stocks
The main impression in recent years is that fishing pressure has been reduced substantially for many North Sea stocks of roundfish and flatfish compared to the beginning of the century. All fish stocks with agreed reference points (Category 1 stocks) are above Blim, apart from cod in Subarea 4, Division 7.d and Subdivision 20. The SSBs of cod in Subarea 4, Division 7.d and Sub-division 20, sole in Subarea 4, and saithe in Division 3.a, Subareas 4 and 6 are below MSY Btrigger at the beginning of 2022. Also, the SSB of witch in Division 3.a, Subarea 4, Division 7.d, estimated in the middle of the year (at spawning time) 2021 is below MSY Btrigger. Several North Sea stocks are exploited at or below FMSY levels (cod in Subarea 4, Division 7.d and Subdivision 20, haddock in Subarea 4, Division 6.a and Subdivision 20, plaice in Subarea 4 and Subdivision 20, sole in Subarea 4, turbot in Subarea 4, whiting in Subarea 4 and Division 7.d); however, several others are being fished above FMSY (saithe in Division 3.a, Subareas 4 and 6, plaice in Division 7.d, witch in Division 3.a, Subarea 4, Division 7.d). An important feature is that recruitment still remains poor compared to historic average levels for most gadoids, although there are signs of a strong recruitment for haddock and whiting in 2019 and 2020. Recruitment in 2020 continues on a high level for flatfish stocks of witch in Division 3.a, Subarea 4 and 7d and for plaice in Subarea 4 and Subdivision 20.
All Nephrops stocks with agreed biomass reference points (Category 1 stocks, excluding nep.fu.3-4) are currently above MSY Btrigger, and all Nephrops stocks with defined FMSY (Category 1 stocks) are being fished below FMSY in 2021, apart from Nephrops in Functional Unit (FU) 6 (nep.fu.6). Assessments and advice will be updated in the autumn.
WGNSSK is also responsible for the assessment of several data-limited species (Category 2+ stocks) that are mainly by-catch in demersal fisheries (brill in Division 3.a, Subarea 4 and Divi-sion 7.d-e, lemon sole in Division 3.a, Subarea 4 and Division 7.d, dab in Division 3.a and Sub-area 4, flounder in Division 3.a and Subarea 4, turbot in Division 3.a, whiting in Division 3.a), along with grey gurnard in Division 3.a, Subarea 4 and Division 7.d and striped red mullet in Division 3.a, Subarea 4 and Division 7.d. Annual advice is required for brill in Division 3.a, Sub-area 4 and Division 7.d-e, turbot in Division 3.a as well as lemon sole in Division 3.a, Subarea 4 and Division 7.d. Biennial precautionary approach (PA) advice for striped red mullet in Division 3.a, Subarea 4 and Division 7.d and flounder in Division 3.a and Subarea 4 was provided in 2015 for the first time, and again in 2017, 2019 and 2021. Biennial advice is required on a different cycle for grey gurnard in Division 3.a, Subarea 4 and Division 7.d as well as whiting in Division 3.a, and was provided in 2022. Triennial advice is now required for dab in Division 3.a and Subarea 4 (due in 2022) and pollack in Division 3.a and Subarea 4 (due in 2024).
The summary of stock status is as follows:
1 ) Nephrops:
This section will be updated in the autumn
2 ) Cod (cod.27.47d20): Spawning-stock biomass has decreased in 2016–2021, but increased in 2022 and is currently below MSY Btrigger, Bpa and Blim. Fishing pressure has decreased since 2018, and is below FMSY in 2021. Recruitment since 1998 remains poor.
3 ) Haddock (had.27.46a20): Spawning-stock biomass has been above MSY Btrigger in most of the years since 2002. Currently, spawning stock size is above MSY Btrigger, Bpa and Blim. Fishing pressure has declined since the beginning of the 2000s, but it has been above FMSY for most of the entire time-series. Since 2019, fishing pressure has been below FMSY. Cur-rently, fishing pressure on the stock is below FMSY, Fpa and Flim. Recruitment since 2000 has been low with occasional larger year classes. The 2019 and 2020 year-classes are estimated to be two of the largest since 2000.
4 ) Whiting (whg.27.47d): Spawning-stock biomass has fluctuated around MSY Btrigger since the mid-1980s and has been above it since 2019. Currently, spawning-stock size is above MSY Btrigger, Bpa and Blim. Fishing pressure has been below FMSY since the early 2000s. Cur-rently, fishing pressure on the stock is below FMSY, Fpa and Flim. Recruitment has been fluc-tuating without trend, but the 2019 and 2020 year-classes are estimated to be the largest since 2002.
5 ) Saithe (pok.27.3a46): Spawning-stock biomass has mostly decreased since the early 2000s and is currently below MSY Btrigger and between Bpa and Blim. Fishing pressure has de-creased and stabilized above FMSY since 2000. Currently, fishing pressure on the stock is above FMSY, but below Fpa and Flim. Recruitment has shown an overall decreasing trend over time with lowest levels in the past 10 years.
6 ) Plaice (ple.27.420): The spawning-stock biomass is well above MSY Btrigger and has mark-edly increased since 2008, following a substantial reduction in fishing pressure since 1999. Currently, fishing pressure on the stock is below FMSY, Fpa and Flim, and spawning-stock size is above MSY Btrigger, Bpa and Blim. After a strong recruitment in 2019, the recruitment in 2020 is estimated to be on an average level.
7 ) Sole (sol.27.4): The spawning-stock biomass has fluctuated around Blim since 2003, and has been estimated to be below MSY Btrigger in 2000–2020. Currently, SSB is estimated to be below MSY Btrigger, and between Bpa and Blim. Fishing pressure has declined since 1999. Currently, fishing pressure on the stock is above FMSY and below Fpa and Flim. Recruitment in 2019 is estimated to be one of the highest in the time series, while recruitment in 2020 and 2021 is estimated to be relatively low.
8 ) Plaice (ple.27.7d): The spawning-stock biomass has increased rapidly from 2010 follow-ing a period of high recruitment between 2009 and 2019, and is now still above the MSY Btrigger, Bpa and Blim despite a decline from 2016 to 2021. Fishing pressure has declined since the early 2000s, with an increase in the recent years to slightly above Fpa. Currently, fish-ing pressure on the stock is above FMSY, but below Fpa and Flim. Recruitment in 2020 is estimated to be the lowest value in the time series, in 2021 it is estimated to be on a rela-tively high level but with large uncertainty.
9 ) Turbot (tur.27.4): The spawning-stock biomass has increased since 2005 and has been above MSY Btrigger since 2013. Currently, spawning stock size is above MSY Btrigger, Bpa and Blim. Fishing pressure has decreased since the mid-1990s, and has been at or below FMSY since 2012. Currently, fishing pressure on the stock is below FMSY, Fpa and Flim. Recruitment is variable without a trend. In 2021, recruitment is estimated to be below average of the time series.
10 ) Witch (wit.27.3a47d): Spawning-stock biomass that was below Blim around 2010, has in-creased since then and is now above Blim but below MSY Btrigger and Bpa. Fishing pressure has been above FMSY since the beginning of the time-series. Currently, fishing pressure on the stock is above FMSY and Fpa, but below Flim. Recruitment has increased in recent years and is currently at high level.
11 ) Norway pout (nop.27.3a4):
This section will be updated in the autumn
12 ) Category 2–6 finfish stocks: In 2022, new advice has been produced for bll.27.3a47de, gug.27.3a47d, dab.27.3a4, lem.27.3a47d, whg.27.3a (all Category 3 stocks) and tur.27.3a (Category 2). Advice was produced following the new WKLIFE X rules. Advice was not provided this year for fle.27.3a4 (Category 3) nor for mur.27.3a47d and pol.27.3a4 (Cate-gory 5).
a) Brill (bll.27.3a47de): The biomass index has been gradually increasing over the time-series until 2015, and has then decreased. Currently, fishing pressure on the stock is above FMSY proxy and the stock size index is above Itrigger.
b) Grey gurnard (gug.27.3a47d): The available survey information indicates a decreas-ing trend in stock biomass in recent years. Currently, the stock size index is above Itrigger; no reference points for fishing pressure have been defined for this stock.
c) Dab (dab.27.3a4): Spawning stock biomass has decreased since 2016. Currently, the stock size index is above Itrigger. Total mortality has been fluctuating without trend over the time series, but is relatively stable in recent years. Currently, fishing pressure is below the FMSY Proxy for this stock. Since the peak in recruitment around the year 2015, there has been a decrease in recent years.
d) Lemon sole (lem.27.3a47d): Spawning-stock biomass mostly decreased from 2012 to 2018, but has recently increased. Currently, the stock size index is well above Itrigger. Currently, fishing pressure is below the FMSY Proxy for this stock.
e) Turbot (tur.27.3a): Catches peaked in the late 1970s and early 1990s and have been more stable in recent years. Relative exploitable biomass (B/BMSY) declined towards 2000 with an increasing trend in recent years. Currently, spawning stock size is above MSY Btrigger. Relative fishing pressure (F/FMSY) peaked in the late 1970s and early 1990s, and has been relatively low without a trend in more recent years. Currently, fishing pressure on the stock is below FMSY.
f) Whiting (whg.27.3a): The biomass index has been gradually increasing in recent years. Currently, the stock size index is above Itrigger. No reference points for fishing pressure have been defined for this stock.
Summary of retrospective analysis (WKFORBIAS decision tree)
To quantify retrospective patterns in the assessments of category 1 stocks, estimates of five-year retrospective peels are produced for fishing pressure, SSB and recruitment and plotted with con-fidence bounds of the current assessment. The retrospective statistics (Mohn’s rho) are reported as a measure of quality. The decision tree formulated by WKFORBIAS (ICES, 2020) was consid-ered to ensure more consistency in how advice is provided. The only stocks that showed signif-icant retrospective patterns in SSB were sole in 4 (Mohn’s rho above limit of 0.2) and Norway pout in Division 3.a and Subarea 4 (Mohn’s rho above 0.3 for short-lived stocks) (for Norway pout, Mohn’s rho will be looked at again in the autumn). For sole, most of the retrospective peels fall outside the confidence bounds. The stock has recently undergone a benchmark and the ret-rospective pattern could not be solved yet. However, the target F (FMSY) in the forecast for 2023 is well below the FP.05 estimated using EqSim, therefore advice is given as usual this year. For Norway pout all the retrospective peels fall inside the wide confidence bounds. The retrospective pattern should be addressed at a future benchmark.