Working Group on the Assessment of Demersal Stocks in the North Sea and Skagerrak (WGNSSK).

The main terms of reference for 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 benchmarks 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 Multispecies Assessment Methods (WGSAM). Conservation status advice was consid-ered but WGNSSK did not identify any conservation aspects for its stocks. Recent benchmarks Benchmarks that involved WGNSSK stocks were organized in 2023–2024. The WKBFLATFISH benchmark for North Sea sole (sol.27.4) and the WKBGAD benchmark for saithe (pok.27.3a46) were convened to evaluate the appropriateness of data and methods to determine stock status. Nephrops in FU32 (nep.fu.32) joined the WKBMSYSPiCT3 benchmark, which resulted in an ac-cepted SPiCT assessment to produce MSY advice for this stock. 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. Seven stocks with agreed reference points (category 1 stocks) have SSB higher than MSY Btrigger (had-dock in 4, 6.a and 20, plaice in 4 and 20, sole in 4, saithe in 3.a, 4 and 6, turbot in 4, whiting in 4 and 7.d and witch in 3.a, 4 and 7.d). Additionally, Northern Shelf cod (cod in 4, 6.a, 7.d and 20) has two substocks (Northwestern and Viking) with SSB above MSY Btrigger, and one substock (Southern) below Blim. The SSB of sole in 7.d is below Blim, while plaice in 7.d is just above Blim. Several North Sea stocks are exploited at or below FMSY levels (haddock in 4, 6.a and 20, plaice in 4 and 20, plaice in 7.d, saithe in 3.a, 4 and 6, sole in 4, sole in 7.d, turbot in 4, whiting in 4 and 7.d); however, both witch in 3.a, 4 and 7.d and all substocks of Northern Shelf cod (cod in 4, 6.a,7.d and 20) are fished above FMSY. An important feature is that recruitment remains poor com-pared to historical average levels for most gadoids, although there have been signs of strongrecruitment for haddock and whiting in most recent years. However, recruitment in 2023 appearsto be very low for the gadoids and lower than previous years for flatfish stocks, with the excep-tion of plaice in 4 and 20. WGNSSK is also responsible for the assessment of several data-limited species (category 2+ stocks) that are mainly bycatch in demersal fisheries; brill in 3.a, 4 and 7.d–e, lemon sole in 3.a, 4 and 7.d, dab in 3.a and 4, flounder in 3.a and 4, turbot in 3.a, whiting in 3.a, grey gurnard in 3.a, 4 and 7.d, striped red mullet in 3.a, 4, 7.d, and pollack in 3.a and 4. Annual advice is requiredfor brill in 3.a, 4 and 7.d–e, turbot in 3.a as well as lemon sole in 3.a, 4 and 7.d. Biennial advice isrequired for striped red mullet in 3.a, 4 and 7.d (due in 2025), flounder in 3.a and 4 (due in 2025),grey gurnard in 3.a, 4 and 7.d as well as for whiting in 3.a. Triennial advice is now required fordab in 3.a and 4 (due in 2025) and pollack in 3.a and 4. Category 2–6 fish stocks: In 2024, new advice has been produced for bll.27.3a47de and tur.27.3a (category 2) and for gug.27.3a47d, lem.27.3a47d, whg.27.3a (all category 3 stocks), and pol.27.3a4 (category 5). Advice was produced following the WKLIFE X rules. Advice was not provided for dab.27.3a4, fle.27.3a4, and mur.27.3a47d (category 3). The summary of stock status is as follows: Category 1 stocks • Cod (cod.27.46a7d20): Spawning-stock biomass of the Northwestern substock has been fluctuating above MSY Btrigger for most of the time-series and is well above it in 2024. Spawning-stock biomass of the Viking substock has been fluctuating between MSY Btrigger and Blim for most of the time-series and is just above MSY Btrigger in 2024. Spawning-stock biomass of the Southern substock has been fluctuating around MSY Btrigger for most of the time-series until 2016 and has been below Blim since 2017. Fishing pressure has been high throughout the time-series but decreased sharply from 2018 and is currently above FMSY for all three substocks. Recruitment (age 1) in recent years has been low for all three sub-stocks, with 2024 being the lowest recruitment in the time-series for both the Northwest-ern and Viking substocks. • Haddock (had.27.46a20): Spawning-stock biomass has been low since the mid of the 2000s but has increased sharply since 2019 and is now well above MSY Btrigger. Fishing pressure has declined since the beginning of the 2000s, but it has been above FMSY for most of the entire time-series. Since 2021, fishing pressure has been below FMSY. Recruit-ment (age 0) since 2000 has been low with occasional larger year classes. Four recent year classes (2019–2022) have all been above the recent mean. Recruitment in 2023 is estimated to be low. • Nephrops FU 3–4 (nep.fu.3-4): advice in autumn. • Nephrops FU 6 (nep.fu.6): advice in autumn. • Nephrops FU 7 (nep.fu.7): advice in autumn. • Nephrops FU 8 (nep.fu.8): advice in autumn. • Nephrops FU 9 (nep.fu.9): advice in autumn. • Norway pout (nop.27.3a4): advice in autumn. • 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. Recruitment (age 1) in 2022 is the second highest in the time-series, while recruitment in 2023 is above average. • Plaice (ple.27.7d): The spawning-stock biomass has increased rapidly from 2010 follow-ing a period of higher recruitment between 2009 and 2019. However, since 2016, SSB has declined and is now at a level just above Blim. Higher fishing pressure from 2015 onwards and lower recruitment from 2020 onwards contributed to this decrease in SSB. Fishing pressure on the stock is currently situated just below FMSY. Recruitment (age 1) 2022 ap-pears to be above average. • Saithe (pok.27.3a46): Spawning-stock biomass has mostly decreased since the early 2000s and is currently above MSY Btrigger. Fishing pressure has decreased and stabilized above FMSY since 2000. Currently, fishing pressure on the stock is just above FMSY. Recruitment (age 3) has shown an overall decreasing trend over time but slightly increasing in 2022. Recruitment in 2023 is low. • Sole (sol.27.4): The spawning-stock biomass has fluctuated around MSY Btrigger since 1996. Currently, SSB is estimated to be above MSY Btrigger. Fishing pressure has been fluctuating above Flim for a large part of the time-series, but sharply decreased from the beginning of the 2000s. In 2023, fishing pressure is below FMSY. Recruitment (age 0) in 2018 was the 5th highest of the time-series, but decreased sharply in the following years. Recruitment in 2023 is low. • Sole (sol.27.7d): The spawning-stock biomass has decreased since 2014 and is estimated to be fluctuating around Blim since 2017. Currently, SSB is estimated to be below Blim. Fishing pressure has decreased since 2007 and is currently estimated below FMSY. Recruitment (age 1) is estimated to be on a relatively low level since 2012 and the 2023 recruitment is low. • 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. Fishing pressure has decreased since the mid-1990s and has been around FMSY since 2011. Cur-rently, fishing pressure on the stock is below FMSY. Recruitment (age 1) is variable without a trend. In 2021, recruitment is estimated to be the lowest of the time-series, while in 2022 and 2023, it is around the long-term mean. • Whiting (whg.27.47d): Spawning-stock biomass has increased substantially in recent years and is now well above MSY Btrigger. Fishing pressure has been below FMSY since the early 1990s. Currently, fishing pressure on the stock is well below FMSY. Recruitment (age 0) has been fluctuating without trend, but the 2019 and 2020 year classes are estimated to be the largest since 2002. Recruitment in 2023 is one of the lowest of the time-series. • Witch (wit.27.3a47d): Spawning-stock biomass has decreased and been below MSY Btrigger since the end of the 1990s, but is above MSY Btrigger in 2024. Fishing pressure has been above FMSY since the beginning of the time-series. Currently, fishing pressure on the stock is above FMSY but below Fpa and Flim. Recruitment (age 1) has decreased since 2019 and is low in 2023. Category 2 stocks • Brill (bll.27.3a47de): Catches declined sharply in recent years. The relative exploitable biomass (B/BMSY) has been above reference point since the beginning of the time-series. Relative fishing pressure (F/FMSY) has decreased since 2000 and is currently below FMSY. • Nephrops FU 32 (nep.fu.32): advice in autumn. • Turbot (tur.27.3a): Catches peaked in the late 1970s and early 1990s and have been more stable in recent years. The relative exploitable biomass (B/BMSY) has been above reference point since the beginning of the time-series. 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. Category 3 stocks • Dab (dab.27.3a4): rollover advice. • Flounder (fle.27.3a4): rollover advice. • Grey gurnard (gug.27.3a47d): The stock size indicator has decreased since 2017, but is still above Itrigger. • Lemon sole (lem.27.3a47d): The stock size indicator has decreased since 2016, but is still just above Itrigger. Currently, fishing pressure on the stock is below the FMSY proxy. • Striped red mullet (mur.27.3a47d): rollover advice. • Whiting (whg.27.3a): The stock size indicator has decreased since 2015, but is still just above Itrigger. Category 4 stocks • Nephrops FU 33 (nep.fu.33): advice in autumn. • Nephrops FU 34 (nep.fu.34): advice in autumn. • Nephrops FU 10 (nep.fu.10): advice in autumn. Category 5 stocks • Nephrops FU 5 (nep.fu.5): advice in autumn. • Nephrops out of FU (nep.27.4outFU): advice in autumn. • Pollack (pol.27.3a4): Catches in the last two years have slightly increased from a low level. Summary of retrospective analysis (WKFORBIAS decision tree) To quantify retrospective patterns in the assessments of category 1 and 2 stocks, estimates of five-year retrospective peels are produced for fishing pressure, SSB and recruitment, and plotted with confidence 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 considered to ensure more consistency in how advice is provided.