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 Multi Species Assessment Methods (WGSAM). Conservation status advice was con-sidered but WGNSSK did not identify any conservations aspects for its stocks.
Benchmarks in 2022/2023
An inter-benchmark protocol (IBP) meeting took place in June 2022 for sole in Division 7.d, to include adjustments of the assessment model configuration and tuning indices. A benchmark was conducted in the period 2022-2023 for North Sea cod. The result of this benchmark was merging the North Sea cod (cod.27.47d20) and West of Scotland cod (cod.27.6a) into one cod Northern shelf stock (cod.27.46a7d20), but accounting for three substocks using a multi-SAM assessment model. Striped red mullet (mur.27.3a47d) and brill (bll.27.3a47de) joined the WKBM-SYSPiCT 2023 benchmark, which resulted in an accepted SPiCT assessment for brill. SPiCT was not found appropriate for striped red mullet and WKLIFE X methods were explored during the WGNSSK 2023 meeting including an external review.
State of the Stocks
The following section does not contain any result or information regarding, all Nephrops stocks and Norway pout (nop.27.3a4). The information regarding these stocks will be updated later during the year when the related advice will be released.
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. Five 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, saithe in 3.a, 4 and 6, turbot in 4, whiting in 4 and 7.d), while the SSB of sole in 4, sole in 7.d, plaice in 7.d, and witch in 3.a, 4 and 7.d is just above Blim. Northern shelf cod (cod in 4, 6a, 7d and 20) has one substock (Northwestern) with SSB above MSY Btrigger, one substock (Viking) between MSY Btrigger and Blim and one substock (Southern) be-low Blim. Several North Sea stocks are exploited at or below FMSY levels (haddock in 4, 6.a and 20, plaice in 4 and 20, saithe in 3.a, 4 and 6, sole in 4, sole in 7.d, turbot in 4, whiting in 4 and 7.d); however, two stocks are being fished above FMSY (plaice in 7.d, and witch in 3.a, 4 and 7.d). All substocks of Northern shelf cod (cod in 4, 6a, 7d and 20) are fished above FMSY. An important feature is that recruitment remains poor compared to historic average levels for most gadoids, although there are signs of a strong recruitment for haddock and whiting in most recent years. Recruitment in 2022 for flatfish stocks continues on a high level only for witch in 3.a, 4 and 7d and for 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 and 7.d, pollack in 3.a and 4. Annual advice is required for 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 is required for striped red mullet in 3.a, 4 and 7.d, flounder in 3.a and 4, grey gurnard in 3.a, 4 and 7.d (due in 2024) as well as for whiting in 3.a (due in 2024). Triennial advice is now required fordab in 3.a and 4 (due in 2025) and pollack in 3.a and 4 (due in 2024).
Category 2–6 fish stocks: In 2023, new advice has been produced for bll.27.3a47de and tur.27.3a (Category 2) and for fle.27.3a4, lem.27.3a47d and mur.27.3a47d (all Category 3 stocks). Advice was produced following the new WKLIFE X rules. Advice was not provided for dab.27.3a4, gug.27.3a47d and whg.27.3a (Category 3) nor for pol.27.3a4 (Category 5).
The summary of stock status is as follows:
Category 1:
•Cod (cod.27.46a7d20): Spawning-stock biomass of the Northwestern substock has beenfluctuating above MSY Btrigger for most of the time series and is well above it in 2023.Spawning-stock biomass of the Viking substock has been fluctuating between MSY Btriggerand Blim for most of the time series and is just below MSY Btrigger in 2023. Spawning-stockbiomass of the Southern substock has been fluctuating around MSY Btrigger for most of thetime series until 2016 and has been below Blim since 2017. Fishing pressure has been highthroughout the time series but decreased sharply from 2018 and is currently above FMSYfor all three substocks. Recruitment has been low for all 3 substocks, with the lowestrecruitment in the Southern substock.
•Haddock (had.27.46a20): Spawning-stock biomass has been low since the mid of the2000s but has increased sharply since 2019 and is now well above MSY Btrigger, Bpa andBlim. Fishing pressure has declined since the beginning of the 2000s, but it has been aboveFMSY for most of the entire time-series. Since 2021, fishing pressure has been below FMSY.Recruitment (age 0) since 2000 has been low with occasional larger year classes. The last4 year-classes have all been above the recent mean.
•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 since1999. Currently, fishing pressure on the stock is below FMSY. After a strong recruitment(age 1) in 2019, the recruitment in 2020 and 2021 is estimated to be on an average level.Recruitment in 2022 is the second highest in the time series.
•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 hasdeclined and is now at a level just above Blim. Higher fishing pressure from 2015 onwardsand lower recruitment from 2020 onwards contributed to this decrease in SSB. Fishingpressure on the stock is currently situated between FMSY and Fpa. Recruitment (age 1) in2020 is estimated to be the lowest value in the time series. The 2021 recruitment wasslightly higher. The lack of the UK-BTS survey in Division 7.d in 2022 resulted in highuncertainty for the 2022 recruitment estimate.
•Saithe (pok.27.3a46): Spawning-stock biomass has mostly decreased since the early 2000sand is currently above MSY Btrigger, Bpa and Blim. Fishing pressure has decreased and sta-bilized above FMSY since 2000. Currently, fishing pressure on the stock is below FMSY. Re-cruitment (age 3) has shown an overall decreasing trend over time but slightly increasingin 2022.
•Sole (sol.27.4): The spawning-stock biomass has fluctuated around Blim since 1996. Cur-rently, SSB is estimated to be between Blim and MSY Btrigger (= Bpa). Fishing pressure hasbeen fluctuating above Flim for a large part of the time series. In 2022, it declined to levels below FMSY. Recruitment (age 1) in the most recent years has been lower than the long-term average.
•Sole (sol.27.7d): The spawning-stock biomass has decreased since 2014 and is estimatedto be fluctuating around Blim since 2017. Currently, SSB is estimated to be between Blimand MSY Btrigger (= Bpa). Fishing pressure has decreased since 2007 and is currently esti-mated around FMSY. Recruitment (age 1) is estimated to be on a relatively low level since2012 and the 2022 recruitment is the lowest of the time series.
•Turbot (tur.27.4): The spawning-stock biomass has increased since 2005 and has beenabove MSY Btrigger since 2013. Currently, spawning stock size is above MSY Btrigger, Bpa andBlim. Fishing pressure has decreased since the mid-1990s, and has been around FMSY since2012. Currently, fishing pressure on the stock is below FMSY. Recruitment is variable with-out a trend. In 2021, recruitment (age 1) is estimated to be the lowest of the time series.
•Whiting (whg.27.47d): Spawning-stock biomass has increased substantially in recentyears and is now well above MSY Btrigger, Bpa and Blim. Fishing pressure has been belowFMSY since the early 2000s. Currently, fishing pressure on the stock is below FMSY. Recruit-ment (age 0) has been fluctuating without trend, but the 2019 and 2020 year-classes areestimated to be the largest since 2002.
•Witch (wit.27.3a47d): Spawning-stock biomass is now just above Blim but below MSY Btrig-ger and Bpa. 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 increased since 2016.
Category 2:
•Brill (bll.27.3a47de): Catches declined sharply in recent years. The relative exploitablebiomass (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.
•Turbot (tur.27.3a): Catches peaked in the late 1970s and early 1990s and have been morestable in recent years. The relative exploitable biomass (B/BMSY) has been above referencepoint since the beginning of the time series. Relative fishing pressure (F/FMSY) peaked inthe late 1970s and early 1990s, and has been relatively low without a trend in more recentyears. Currently, fishing pressure on the stock is below FMSY.
Category 3:
•Dab (dab.27.3a4): rollover advice.
•Flounder (fle.27.3a4): The stock size indicator has been fluctuating below Itrigger for thepast 6 years. Currently, fishing pressure on the stock is below the FMSY proxy.
•Grey gurnard (gug.27.3a47d): rollover advice.
•Lemon sole (lem.27.3a47d): The stock size indicator has decreased since 2016, but is stillabove Itrigger. Currently, fishing pressure on the stock is below the FMSY proxy.
•Striped red mullet (mur.27.3a47d): The stock size indicator is well-above the Itrigger. Cur-rently the fishing pressure on the stock is above the FMSY proxy.
•Whiting (whg.27.3a): rollover advice.
Category 4:
•Nephrops FU 32 (nep.fu.32): rollover advice.
•Nephrops FU 33 (nep.fu.33): rollover advice.
•Nephrops FU 34 (nep.fu.34): rollover advice.
•Nephrops FU 10 (nep.fu.10): rollover advice.
Category 5:
•Nephrops FU 5 (nep.fu.5): rollover advice.
•Nephrops out of FU (nep.27.4outFU): rollover advice.Pollack (pol.27.3a4): rollover advice.
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. The only stock that showed significant retrospective patterns in SSB was sole in Subarea 4 (Mohn’s rho above limit of 0.2). For sole, all of the retrospective peels fall outside the confidence bounds. The stock is scheduled for benchmark in 2023/2024, during which the retrospective pattern will be investigated. Unlike last year, the target F (FMSY) in the forecast for 2024 is now above the FP.05 estimated using EqSim. Following the WKFORBIAS decision tree, WGNSSK decided to adjust the numbers at age in the intermediate year (2023) using the five-year average SSB Mohn’s rho prior to forecasting.