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 considered 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. Norway lobster in FU32 (nep.fu.32) joined the WKBMSYSPiCT3 benchmark, which resulted in an accepted 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 B_trigger (haddock 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 B_trigger, and one substock (Southern) below B_lim. Finally, all category 1 Norway lobster stocks (for which a reference point for stock size is determined) have a stock size above MSY B_trigger, except for Functional Unit 6. The SSB of sole in 7.d is below B_lim, while plaice in 7.d is just above B_lim. The SSB of Norway pout is estimated above B_pa (no MSY B_trigger reference points is defined for this stock). Several North Sea stocks are exploited at or below F_MSY 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, Norway lobster in FUs 7, 8 and 9); however, witch in 3.a, 4 and 7.d, all substocks of Northern Shelf cod (cod in 4, 6.a, 7.d and 20) and Norway lobster in FU 6 are fished above F_MSY. An important feature is that recruitment remains poor compared to historical average levels for most gadoids, although there have been signs of strong recruitment for haddock and whiting in most recent years. However, recruitment in 2023 appears to be very low for the gadoids and lower than previous years for flatfish stocks, with the exception 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, pollack in 3.a and 4 and Norway lobster in FUs 5, 10, 32, 33, 34 and area 4 out of FUs. Annual advice is required for brill in 3.a, 4 and 7.d–e, turbot in 3.a, lemon sole in 3.a, 4 and 7.d as well as Norway lobster in FU 32. Biennial advice is required 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, whiting in 3.a as well as for Norway lobster in FUs 5, 10, 33, 34 and area 4 out of FUs. Triennial advice is now required for dab 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, tur.27.3a, nep.fu.32 (category 2), for gug.27.3a47d, lem.27.3a47d, whg.27.3a (category 3), nep.fu.10, nep.fu.33 and nep.fu.34 (category 4), and pol.27.3a4, nep.fu.5 and nep.27.4outFU (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 B_trigger 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 B_trigger and B_lim for most of the time-series and is just above MSY B_trigger in 2024. Spawning-stock biomass of the Southern substock has been fluctuating around MSY B_trigger for most of the time-series until 2016 and has been below B_lim since 2017. Fishing pressure has been high throughout the time-series but decreased sharply from 2018 and is currently above F_MSY for all three substocks. Recruitment (age 1) in recent years has been low for all three substocks, with 2024 being the lowest recruitment in the time-series for both the Northwestern 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 B_trigger. Fishing pressure has declined since the beginning of the 2000s, but it has been above F_MSY for most of the entire time-series. Since 2021, fishing pressure has been below F_MSY. Recruitment (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): Fishing pressure slowly increased from 2017-2021, shows a slight decrease in 2022-2023, but is still below F_MSY. Stock size is decreasing from 2017-2021, shows a slight increase in 2023 and a decrease in 2024. No reference point for stock size has been defined for this stock.

· Nephrops FU 6 (nep.fu.6): Fishing pressure has been fluctuating above F_MSY (with the exception of 2008). Stock size was below MSY B_trigger in 2009, 2010 and from 2012-2016, and in 2024.

· Nephrops FU 7 (nep.fu.7): Over the last decade, fishing pressure is well-below F_MSY and stock size is well-above MSY B_trigger.

· Nephrops FU 8 (nep.fu.8): Stock size has been above MSY B_trigger for the entire time series, while fishing pressure has been fluctuating around F_MSY. In 2023, fishing pressure is below F_MSY.

· Nephrops FU 9 (nep.fu.9): Fishing pressure has been fluctuating around F_MSY, and is below the reference point in 2023. Stock size was estimated to be largely above MSY B_trigger, and this is also the case in 2024.

· Norway pout (nop.27.3a4): Spawning-stock biomass has been fluctuating over the time-series with period of higher biomass in the 1990s and later 2000s, as well as in the late 2010s. In the most recent year, SSB decreased, but is still above B_pa and B_lim. No reference points for fishing pressure or for MSY B_trigger have been defined for this stock. Recruitment was below average in 2021 and is very low in 2023 and 2024.

· Plaice (ple.27.420): The spawning-stock biomass is well above MSY B_trigger and has markedly increased since 2008, following a substantial reduction in fishing pressure since 1999. Currently, fishing pressure on the stock is below F_MSY. 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 following a period of higher recruitment between 2009 and 2019. However, since 2016, SSB has declined and is now at a level just above B_lim. 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 F_MSY. Recruitment (age 1) 2022 appears to be above average.

· Saithe (pok.27.3a46): Spawning-stock biomass has mostly decreased since the early 2000s and is currently above MSY B_trigger. Fishing pressure has decreased and stabilized above F_MSY since 2000. Currently, fishing pressure on the stock is just above F_MSY. 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 B_trigger since 1996. Currently, SSB is estimated to be above MSY B_trigger. Fishing pressure has been fluctuating above F_lim for a large part of the time-series, but sharply decreased from the beginning of the 2000s. In 2023, fishing pressure is below F_MSY. Recruitment (age 0) in 2018 was the 5^th 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 B_lim since 2017. Currently, SSB is estimated to be below B_lim. Fishing pressure has decreased since 2007 and is currently estimated below F_MSY. 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 B_trigger since 2013. Currently, spawning stock size is above MSY B_trigger. Fishing pressure has decreased since the mid-1990s and has been around F_MSY since 2011. Currently, fishing pressure on the stock is below F_MSY. 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 B_trigger. Fishing pressure has been below F_MSY since the early 1990s. Currently, fishing pressure on the stock is well below F_MSY. 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 B_trigger since the end of the 1990s, but is above MSY B_trigger in 2024. Fishing pressure has been above F_MSY since the beginning of the time-series. Currently, fishing pressure on the stock is above F_MSY but below F_pa and F_lim. 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/B_MSY) has been above reference point since the beginning of the time-series. Relative fishing pressure (F/F_MSY) has decreased since 2000 and is currently below F_MSY.

· Nephrops FU 32 (nep.fu.32): Catches in the most recent decade are lower than before. The relative exploitable biomass (B/B_MSY) has decreased and is below the reference point since 2007. The relative fishing pressure (F/F_MSY) has increased and is above the reference points since 1999.

· 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/B_MSY) has been above reference point since the beginning of the time-series. Relative fishing pressure (F/F_MSY) 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 F_MSY.

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 I_trigger.

· Lemon sole (lem.27.3a47d): The stock size indicator has decreased since 2016, but is still just above I_trigger. Currently, fishing pressure on the stock is below the F_{MSY 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 I_trigger.

Category 4 stocks

· Nephrops FU 33 (nep.fu.33): The stock and exploitation status are unknown. Landings have been fluctuating around 1000 tonnes over the last two decades. The mean density of Norway lobster decreased from 2021 to 2023.

· Nephrops FU 34 (nep.fu.34): The stock and exploitation status are unknown. Landings have been fluctuating over the time series, but are in the most 5 recent years relatively stable (around 800 tonnes). The mean density of Norway lobster remained stable from 2021 to 2024 (around 400 million).

· Nephrops FU 10 (nep.fu.10): The stock and exploitation status are unknown. Landings have been very low since 2012. The mean density of Norway lobster increased from 2014 to 2019, but decreased again in 2023. .

Category 5 stocks

· Nephrops FU 5 (nep.fu.5): The stock and exploitation status are unknown. Catches have been fluctuating around 1000 tonnes, with the exception of the years 2015-2017, which were around 3000 tonnes. Catches in 2023 decreased compared to 2021-2022. .

· Nephrops out of FU (nep.27.4outFU): The stock and exploitation status are unknown.

· Pollack (pol.27.3a4): Catches in the last two years have slightly increased from a low level.