Witch Glyptocephalus cynoglossus
Publication of Advice: 6 June 2025. Published by Marine and Freshwater Research Institute.
Advice
MFRI advises that when the MSY approach is applied, catches in each of the fishing years 2025/2026 and 2026/2027 should be no more than 1 659 tonnes.
Stock development
Stock size is above Itrigger and the fishing pressure is below FMSY proxy.
Witch. Catch by gear type, IS-SMB juvenile index (<25 cm), fishing pressure proxy and IS-SMB biomass (≥30 cm) index. IS-SMB juvenile index: the error bars show 95% confidence intervals. IS-SMB biomass index: the red horizontal lines indicate average biomass indices for 2021–2023 and for 2024–2025 used in the advice calculations; the shaded area shows 95% confidence intervals.
Basis of the assessment and reference points
Basis of the advice | MSY approach |
Management plan | There is no management plan for this stock |
Assessment type | Trends in biomass indicators |
Input data | Commercial catch and survey biomass indices (IS-SMB) |
Approach | Reference point | Value | Basis |
|---|---|---|---|
MSY approach | Itrigger | 1 182 | Iloss×1.4, Iloss defined as the lowest survey value |
FMSY_proxy | 1 | Relative value from LBI analysis, assuming M/K = 1.5. | |
Lc | 33 | Length at first capture, 50% modal abundance from catch length data | |
LInf | 60 | Asymptotic length, defined as maximum length from catch length data | |
K | 0.15 | Population growth rate | |
LF=M | 39.75 | 0.75 x Lc + 0.25 x LInf |
Prospects
The ICES framework for category 3 stocks, for which analytical assessment is not possible but trends in biomass indicators are assumed to reflect changes in stock dynamics, was applied (ICES, 2025). IS-SMB biomass index of dab ≥25 cm is used as an indicator of stock development. As sufficient data on life history in addition to length measurements from catches, the advice is based on the new rfb-rule for ICES category 3 data-limited stocks and is valid for each of the fishing years 2025/2026 and 2026/2027.
Witch. Advice calculation.
Ay: Catch advice for 2024/2025 | 1 476 |
Stock biomass trend | |
Index A (2024-2025) | 3 323 |
Index B (2021-2023) | 3 180 |
r: Stock biomass trend (index ratio A/B) | 1.045 |
Fishing pressure proxy | |
Mean catch length (Lmean = L2024) | 45 |
MSY proxy length (LF=M) | 40 |
f: Fishing pressure proxy (LF=M/Lmean) | 0.883 |
Biomass safeguard | |
Last index value (I2025) | 3 939 |
Index trigger value (Itrigger=Iloss*1.4) | 1 182 |
b: Index relative to trigger value, min{I2025/Itrigger, 1} | 1 |
Precautionary multiplier to maintain biomass above Blim with 95% probability | |
m: Multiplier (generic multiplier based on life history) | 0.95 |
Advice calculation1) | 1 659 |
Stability clause (+20% / -30% compared to Ay, only applied if b>1)2) | 0 |
Catch advice for 2025/2026 and 2026/2027 | 1 659 |
% advice change3) | 12 |
1) Ay × r × 1/f × b × m | |
2) min{max(0.7Ay, Ay+1), 1.2Ay} | |
3) The figures in the table are rounded. Calculations were done with unrounded inputs, and compared values may not match exactly when calculated using the rounded figures in the table. | |
The advice for each of the fishing years 2025/2026 and 2026/2027 is higher than the advice for 2024/2025 because the stock size indicator has increased.
Quality of the assessment
The IS-SMB covers the main fishing grounds of witch. Year-to-year fluctuations in the survey biomass index can be considerable.
Other information
Recruitment was low during 2012–2020 but has increased in recent years.
Advice, tac and catch
Witch. Recommended TAC, national TAC, and landings (tonnes)
Fishing year | Recommended TAC | National TAC | Total catch |
|---|---|---|---|
1994/1995 | 1 500 | 1 642 | |
1995/1996 | 1 400 | 1 699 | |
1996/1997 | 1 200 | 1 200 | 1 300 |
1997/1998 | 1 100 | 1 100 | 995 |
1998/1999 | 1 100 | 100 | 1 176 |
1999/2000 | 1 100 | 1 100 | 1 117 |
2000/2001 | 1 100 | 1 100 | 1 166 |
2001/2002 | 1 350 | 1 350 | 1 225 |
2002/2003 | 1 500 | 1 500 | 1 534 |
2003/2004 | 1 500 | 1 500 | 2 000 |
2004/2005 | 2 000 | 2 000 | 2 246 |
2005/2006 | 2 200 | 2 400 | 2 190 |
2006/2007 | 2 000 | 2 400 | 2 197 |
2007/2008 | 2 000 | 2 400 | 1 543 |
2008/2009 | 1 600 | 2 200 | 1 707 |
2009/2010 | 1 600 | 2 200 | 1 296 |
2010/2011 | 1 300 | 1 300 | 1 222 |
2011/2012 | 1 100 | 1 300 | 1 452 |
2012/2013 | 1 100 | 1 100 | 1 183 |
2013/2014 | 1 100 | 1 100 | 1 168 |
2014/2015 | 1 100 | 1 100 | 1 225 |
2015/2016 | 1 100 | 1 100 | 1 148 |
2016/2017 | 1 110 | 1 110 | 1 088 |
2017/2018 | 1 116 | 1 116 | 885 |
2018/2019 | 1 100 | 1 100 | 844 |
2019/2020 | 1 067 | 1 067 | 940 |
2020/2021 | 854 | 854 | 733 |
2021/2022 | 1 025 | 1 025 | 603 |
2022/2023 | 1 230 | 1 230 | 632 |
2023/2024 | 1 476 | 1 476 | 622 |
2024/2025 | 1 476 | 1 476 | |
2025/2026 | 1 659 | ||
2026/2027 | 1 659 |
References and further reading
ICES. 2025. ICES Guidelines - Advice rules for stocks in category 2 and 3. Version 3. ICES Guidelines and Policies - Advice Technical Guidelines. 31 pp. https://doi.org/10.17895/ices.pub.28506179
MFRI Assessment Reports 2025. Witch. Marine and Freshwater Research Institute, 6 June 2025.