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

Alessandro Orio, Alexander Kempf, Alexandros Kokkalis, Andreas Sundelöf, Carlos Mesquita, Chun Chen, Clara Ulrich, Coby Needle, Francesca Vitale, Guldborg Søvik, Harriet Cole, Holger Haslob, J. Rasmus Nielsen, Jon Egil Skjæraasen, José De Oliveira, Jurgen Batsleer, Knut Korsbrekke, Lies Vansteenbrugge, Marc Taylor, Mats UlmestrandRaphaël Girardin, Rosana Ourens, Ruben Verkempynck, Sarah Millar, Tanja Miethe, Wouter van Broekhoven, Gwladys Lambert, Ewen Bell, Jordan P. Feekings, Nicola Walker, Youen Vermard

Research output: Book/ReportReportResearch

8 Downloads (Pure)

Abstract

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 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).

Benchmarks and Inter-benchmarks in 2018/2019
No full benchmarks were conducted during 2019 for WGNSSK stocks. However, there were several inter-benchmark protocol (IBP) meetings during 2018/2019. These were on North Sea turbot and saithe, and on sole in 7.d.

State of the Stocks
The main impression in recent years is that fishing mortality 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 4, 7.d and 20, and only the SSBs of cod in 4, 7.d and 20 and whiting in 4 and 7.d are below MSY Btrigger at the beginning of 2019. Several North Sea stocks are exploited at or below FMSY levels (saithe in 3.a, 4 and 6, plaice in 4 and 20, plaice in 7.d, sole in 7.d, and turbot in 4); however, just as many are being fished above FMSY (cod in 4, 7.d and 20, haddock in 4, 6.a and 20, whiting in 4 and 7.d, sole in 4, and witch in 3.a, 4 and 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 in 2019 (the strongest since the 1999 year-class; to be confirmed with future data).

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, including nep.fu.3-4) are being fished at or below FMSY in 2018, apart from Nephrops in FU 6 (nep.fu.6).

WGNSSK is also responsible for the assessment of several data-limited species (Category 3+stocks) that are mainly by catch 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 3a), along with striped red mullet in 3.a, 4 and 7.d. Biennial precautionary approach (PA) advice was provided in 2015 for the first time, and again in 2017; for 2019, biennial advice was either PA, where catch advice was still needed, or simply reporting stock status where no catch advice was needed. Reopening of advice was triggered for several Category 1 stocks in the autumn, following the availability of Q3 survey results in 2019, namely cod in 4, 7.d and 20, haddock in 4, 6.a and 20, plaice in 4 and 20, sole in 4, and Nephrops in FU 6, 7 and 8 (Annex 7).

The summary of stock status is as follows:

1) Nephrops:
Category 1:
a) FU 3-4 (nep.fu.3-4): The stock size is considered to be stable. The estimated harvest rate for this stock is currently below FMSY. No reference points for stock size have been
defined for this stock.
b) FU 6 (nep.fu.6): The stock abundance has increased since 2015, and currently it is above MSY Btrigger. The harvest rate has shown a decreasing trend since 2013, and is
just above FMSY in 2018.
c) FU 7 (nep.fu.7): The stock size has been above MSY Btrigger for most of the time-series. The harvest rate has declined since 2010 and remains well below FMSY.
d) FU 8 (nep.fu.8): The stock size has been above MSY Btrigger for the entire time-series. The harvest rate is varying and is now below FMSY.
e) FU 9 (nep.fu.9): The stock has been above MSY Btrigger for the entire time-series. The harvest rate has fluctuated around FMSY in recent years and is now just below FMSY.
Category 4:
f) FU 33 (nep.fu.33): The state of this stock is unknown. Landings have been relatively stable since 2004, fluctuating without trend at around 1000 tonnes. The mean density
of Norway lobster decreased by 43% from 2017 to 2018. Advice was provided for this stock in 2019 (although it was not scheduled) because of the availability of data from
a UWTV survey conducted in 2018.

No new advice was provided in 2019 for Nephrops outside the functional units (nep.27.4outFU; Category 5), and for the remaining Category 4 Nephrops stocks (nep.fu.5,
nep.fu.10, nep.fu.32, nep.fu.34).

A workshop on Methodologies for Nephrops Reference Points (WKNephrops) is being held 25–29 November 2019 to evaluate reference point estimation for stocks with UWTV
surveys. This workshop will also consider a consistent methodology to determine stock status and provide catch advice for data-limited Nephrops stocks, taking into account
available data and knowledge from other areas.

2) Cod (cod.27.47d20): Fishing mortality has increased since 2016, and is above Flim in 2018. Spawning-stock biomass has decreased since 2015 and is now below Blim. Recruitment since 1998 remains poor. Currently, fishing pressure on the stock is above FMSY, Fpa, and Flim; the spawning-stock size is below MSY Btrigger, Bpa, and Blim.
3) Haddock (had.27.46a20): Fishing mortality has declined since the beginning of the 2000s, but it has been above FMSY for the entire time-series. Spawning-stock biomass has been above MSY Btrigger in most of the years since 2002. Recruitment since 2000 has been low with occasional larger year classes. The 2019 year-class is estimated to be the largest since 2000. Currently, fishing pressure on the stock is above FMSY but below Fpa and Flim, and spawning stock size is above MSY Btrigger, Bpa, and Blim.
4) Whiting (whg.27.47d): Spawning-stock biomass has fluctuated around MSY Btrigger since the mid-1980s and is just below it in 2019. Fishing mortality has been above FMSY throughout the time-series, apart from 2005. Recruitment (R) has been fluctuating without trend, but the last two year-classes are below average. Currently, fishing pressure on the stock is above FMSY, but below Fpa and Flim; spawning-stock size is below MSY Btrigger and Bpa, but above Blim.
5) Saithe (pok.27.3a46): Spawning-stock biomass has fluctuated without trend and has been above MSY Btrigger since 1996. Fishing mortality has decreased and stabilized at or below FMSY since 2014. Recruitment has shown an overall decreasing trend over time with lowest levels in the past 10 years. Currently, fishing pressure on the stock is at FMSY and below Fpa and Flim; spawning-stock size is above MSY Btrigger, Bpa and Blim.
6) Plaice (ple.27.420): The spawning-stock biomass is well above MSY Btrigger and has markedly increased since 2008, following a substantial reduction in fishing mortality since 1999. Recruitment in 2019 is estimated to be the second highest in the time-series. Since 2009, fishing mortality has been estimated below FMSY. Currently, fishing pressure on the stock is below FMSY, Fpa, and Flim, and that spawning-stock size is above MSY Btrigger, Bpa, and Blim.
7) Sole (sol.27.4): The spawning-stock biomass has increased since 2007, and has been estimated above MSY Btrigger since 2012. Fishing mortality has declined since 1999 and is close to FMSY in 2018. Recruitment in 2019 is estimated to be the highest since 1988. Currently, fishing pressure on the stock is above FMSY but below Fpa and Flim, and spawning-stock size is above MSY Btrigger, Bpa, and Blim.
8) Plaice (ple.27.7d): The spawning-stock biomass has increased rapidly from 2010 following a period of high recruitment between 2009 and 2015, and is now still well above the MSY Btrigger, despite a decline since 2016. Fishing mortality has declined since the early 2000s, with an increase in the recent years to slightly below FMSY. Recruitment is currently around the average of the last 10 years of the time series. Currently, fishing pressure on the stock is below FMSY, Fpa, and Flim, and spawning stock size is above MSY Btrigger, Bpa, and Blim.
9) Sole (sol.27.7d): The spawning-stock biomass (SSB) has been fluctuating without trend and has been above MSY Btrigger since 2017. Fishing mortality has been decreasing trend since 2009 and has been below FMSY since 2017. Recruitment has been fluctuating without trend. Currently, fishing pressure on the stock is below FMSY proxy, Fpa, and Flim; spawningstock size is above MSY Btrigger proxy and above Bpa and Blim. This stock underwent an interbenchmark during 2019 to incorporate revised tuning indices and re-estimate reference points, but was subsequently down-graded to a Category 3 assessment due to unreliable plus-group data and plus-group estimation that led to a large increase in advice. The assessment is currently indicative of trends only. A full benchmark is planned for early 2020.10) Turbot (tur.27.4): Recruitment is variable without a trend. Fishing mortality has decreased since the mid-1990s, and has been just below FMSY since 2012. The spawning-stock biomass has increased since 2005 and has been above MSY Btrigger since 2013. This stock was upgraded to Category 1 from Category 3 following an inter-benchmark during 2018. Currently, fishing pressure on the stock is below FMSY, Fpa, and Flim; spawning stock size is above MSY Btrigger, Bpa, and Blim.
11) Witch (wit.27.3a47d): Fishing mortality has been above FMSY since the beginning of the time-series. Spawning-stock biomass that was below Blim around 2010, has increased since then and is now above MSY Btrigger. Recruitment has declined since 2010 and is currently at a low level. This stock was upgraded to Category 1 from Category 3 following a benchmark during 2018. Currently, fishing pressure on the stock is above FMSY and between Fpa
and Flim, and spawning stock size is above MSY Btrigger, Bpa, and Blim.
12) Norway pout (nop.27.3a4): The stock size is highly variable from year to year, due to recruitment variability and a short life span. Spawning-stock biomass is estimated to have been fluctuating above Bpa for most of the time-series. Fishing mortality declined between 1985 and 1995 and has been fluctuating at a lower level since 1995. Recruitment in 2018 and 2019 was above the long-term average. Currently, spawning stock size is above Bpa and Blim; no reference points for fishing pressure or for MSY Btrigger have been defined for this stock.
13) Category 3–6 finfish stocks: In 2019, new advice has been produced for bll.27.3a47de, dab.27.3a4, fle.27.3a4, lem.27.3a47d, mur.27.3a47d, tur.27.3a (all Category 3 stocks) and whg.27.3a (Category 5). Although not requested, advice was provided for dab.27.3a4 to deal with an advice gap left by the Commission changing the advice cycle for dab from 2 to 3 years. Advice was not provided for gug.27.3a47d (Category 3) and pol.27.3a4 (Category 5).
a) Brill (bll.27.3a47de): The biomass index has been gradually increasing over the timeseries until 2015, and has then decreased. Currently, fishing pressure on the stock is below FMSY proxy and spawning stock size is above MSY Btrigger proxy.
b) Dab (dab.27.3a4): The biomass has been increasing since the start of the time-series, but has declined since its peak in 2016. Total mortality is fluctuating without trend.
Recruitment showed an increasing trend until 2014, but has declined since then. Currently, fishing pressure on the stock is below FMSY proxy, and the spawning stock size is above MSY Btrigger proxy.
c) Flounder (fle.27.3a4): The available survey information indicates no clear trend in stock biomass. Currently, fishing pressure on the stock is below FMSY; no reference points for stock size have been defined for this stock.
d) Lemon sole (lem.27.3a47d): Total mortality has fluctuated without trend. Spawningstock biomass increased from 2007 to 2012, and has remained stable since, albeit with a small decline in 2018. Recruitment has shown a mostly downwards trend since a peak in 2011. Currently, fishing pressure on the stock is below FMSY. No reference points for stock size have been defined for this stock.
e) Striped red mullet (mur.27.3a47d): Spawning-stock biomass has decreased since 2015 as a consequence of poor recruitment and an increase in F. Recruitment in 2018 is
estimated to be large. ICES cannot assess the stock and exploitation status relative to MSY and precautionary approach reference points because the reference points are undefined.
f) Turbot (tur.27.3a): The IBTS Q1 biomass index is variable and has been fluctuating without trend over time. The IBTS Q3 biomass index is also variable but has shown
an increased level after 2005. ICES cannot assess the stock and exploitation status relative to MSY and precautionary approach reference points because the reference points are undefined.
g) Whiting (whg.27.3a): Catches have been relatively low in recent years after a substantial industrial fishery ceased in the mid-1990s. ICES cannot assess the stock and exploitation status relative to MSY and precautionary approach reference points because the reference points are undefined.
Original languageEnglish
Place of PublicationCopenhagen, Denmark
PublisherICES
Number of pages1,271
DOIs
Publication statusPublished - 2019
SeriesICES Scientific Report
Number7
Volume1
ISSN2618-1371

Fingerprint

Dive into the research topics of 'Working Group on the Assessment of Demersal Stocks in the North Sea and Skagerrak (WGNSSK)'. Together they form a unique fingerprint.

Cite this