Whiting

Merlangius merlangus


Technical report
Published by

Marine and Freshwater Research Institute, Iceland

Published

12 June 2026

Key signals

  • Since the initiation of the spring survey in 1985, survey biomass has peaked approximately every 15 years — first in 1990, followed by a larger peak in 2005, and the highest peak in 2024.

  • Recruitment has followed a similar pattern, with peaks occurring one to three years before the corresponding peaks in the total biomass index.

  • Spawning stock biomass (SSB) has been above \(I_{trigger}\) since 2017.

  • Fishing pressure has been below \(HR_{MSY~proxy}\) since 2017.

General information

Whiting is a demersal gadoid species like cod and haddock, but smaller with a maximum length of about 80 cm, males and females being similar in size. In Icelandic waters, sexual maturity is reached at around 30 cm.

Fishery

Whiting has been caught mainly as bycatch all around Iceland in recent years, though mostly to the south and west of Iceland (Figure 1 and Figure 2). Annual catches have been between 500 and 1000 tonnes except for 2008-2012 when catches increased peaking in 2011 at 2602 tonnes (Figure 2). Increased catches in this period occurred almost exclusively in the southwest (Figure 2). In 2021 and 2023, catches were slightly higher than in adjacent years, comparable to 2013 levels, but otherwise remained low (Figure 2, Figure 3, Figure 4 and Figure 6). Whiting is found at depths ranging from 10 to 300 m but is mostly caught between 100 and 250 m (Figure 3).

Whiting is mainly caught in demersal trawls but to some extent in Nephrops trawls, on longlines and with demersal seine (Table 1, Figure 4). The number of vessels reporting whiting catches increased alongside the rise in catches between 2007 and 2012 but has since then decreased, reaching its lowest point in 2018 (Figure 5).

Figure 1: Whiting. Spatial distribution of catches by all gears.
Figure 2: Whiting. Changes in spatial distribution of whiting catches as recorded in Icelandic logbooks.
Figure 3: Whiting. Depth distribution of whiting catches from bottom trawls, longlines, trawls and demersal seine from Icelandic logbooks
Figure 4: Whiting. Landings in tons and percent of total by gear and year
Figure 5: Whiting. Number of vessels (all gear types) accounting for 95% of the total catch annually since 1994. Left: Plotted against year. Right: Plotted against total catch. Data from the Directorate of Fisheries.
Table 1: Whiting. Number of Icelandic vessels landing whiting, and all landed catch divided by gear type.
Year Nr. Bottom Trawl Nr. Other Nr. Long Line Nr. Danish Seine Bottom Trawl Other Long Line Danish Seine Total catch
2000 86 103 170 25 1088 23 157 76 1344
2001 76 129 139 25 929 66 114 64 1173
2002 88 133 116 18 1068 48 90 93 1299
2003 72 111 133 27 733 37 153 102 1025
2004 68 110 142 25 704 26 224 84 1038
2005 77 107 171 34 518 11 205 63 797
2006 62 106 189 37 467 23 460 100 1050
2007 66 86 216 43 767 26 394 71 1258
2008 77 95 235 49 950 30 557 151 1688
2009 77 221 244 60 1439 45 520 303 2307
2010 63 276 212 50 2192 42 425 191 2850
2011 65 263 219 43 2486 24 345 109 2964
2012 65 263 223 45 956 19 320 174 1469
2013 53 234 218 41 659 7 255 62 983
2014 52 174 208 32 643 7 207 73 930
2015 44 160 186 30 675 4 116 65 860
2016 41 114 174 30 559 2 104 69 734
2017 34 64 147 24 401 1 108 43 553
2018 38 37 115 21 688 1 61 67 817
2019 47 64 109 26 605 1 93 61 760
2020 47 61 102 20 548 2 67 18 635
2021 48 103 93 25 820 3 59 71 953
2022 48 101 78 26 631 3 67 72 773
2023 49 159 65 30 957 12 112 64 1145
2024 49 105 63 23 600 4 87 46 737
2025 51 130 62 28 644 7 107 49 807

Length Distributions from commercial catches of whiting

Samples from commercial catches are mostly collected in the south west, where whiting is most abundant (Figure 6). Length measurements from commercial catches are scarce and missing for some years, but show substantial recruitment in 1980, 1996, 2007 and 2019 (Figure 7). Most whiting caught in the commercial fishery are 38-55 cm.

Figure 6: Whiting. Distribution of samples from commercial catches.
Figure 7: Whiting. Commercial length distributions from bottom trawls.

Survey data

Annual Icelandic groundfish surveys have been conducted in March (IS-SMB) since 1985 and in October (IS-SMH) since 1996, except in 2011. Both surveys cover the distribution area of whiting on Icelandic grounds. For monitoring, harvestable biomass and recruitment indices were estimated for both surveys (Figure 8). The harvestable biomass index is calculated as the biomass of individuals 40 cm and larger. The recruitment index is defined as whiting smaller than 20 cm.

Both the total biomass index and harvestable biomass index in IS-SMB increased from 2003 to a maximum in 2005 but decreased to a low level in 2015 (Figure 8). Since then, both indices have increased, and harvestable biomass was approaching the highest value in the timeseries (1990) in 2024 followed by a substantial decrease. The biomass indices from IS-SMH are much more variable but show similar trends as IS-SMB. Recruitment indices show similar trends in both surveys (Figure 8). Strong recruitment was observed in 2003, 2007, 2019-2021, 2024 and 2025 in IS-SMH and in 2004, 2008 and 2021-2022 in IS-SMB. These peaks can be observed in the length distributions (Figure 9), and in the harvestable biomass indices 2-3 years later.

Spatial distribution of whiting from the spring survey is similar to what is observed in commercial catches, that is, mostly in the south of Iceland (Figure 1, Figure 2, Figure 10 and Figure 11). The autumn survey however shows the highest indices in a larger area, southeast, southwest, and west (Figure 12 and Figure 13). The recent increase in the biomass indices has mostly taken place in the southeast and southwest areas (Figure 11 and Figure 13).

Figure 8: Whiting. Total biomass indices (upper left), harvestable biomass indices (>39 cm, upper right), and juvenile abundance indices (<21 cm, lower) from IS-SMB (blue) since 1985 and IS-SMH (red) since 1996, along with 95% CI.
Figure 9: Whiting. Length disaggregated abundance indices from the Autumn survey (October) 1996 onwards and the spring survey (March) 1985 and onwards.
Figure 10: Whiting. Spatial distribution from IS-SMB in the current year.
Figure 11: Whiting. Spatial distribution of biomass index from IS-SMB since 1985.
Figure 12: Whiting. Spatial distribution of catches from IS-SMH last year.
Figure 13: Whiting. Spatial distribution of biomass index from IS-SMH since 1996, excluding 2011.

Stock assessment

The assessment is for this stock based on ICES constant harvest rate \((chr)\)-rule for data limited stocks, where a constant harvest rate (Fproxy,MSY), that can be considered a proxy for harvest rate at maximum sustainable yield, is applied to the spawning stock biomass index (ICES 2025). The \(\text{chr}\)-rule has the following form:

\[A_{y + 1} = I_{y}\ HR_{\text{MSY }\text{proxy}}\ b\ m\]

where \(A_{y + 1}\) is the advised catch, \(I_{y - 1}\) is the last year’s index, \(HR_{MSY proxy}\) is the fishing pressure proxy at MSY, \(b\) is a biomass safeguard (reducing the catch when biomass index drops below a trigger value) and m is a multiplier that is applied to maintain the probability of the biomass declining below \(B_{\lim}\) under 5%.

\(F_{\text{MSY }\text{proxy}}\) is the ratio of the catch and index for the set of historical years (U) where \(f\) > 1:

\[HR_{\text{MSY }\text{proxy}} = \frac{1}{u}\begin{matrix} \sum_{y \in U}^{}\frac{C_{y}}{I_{y}} \\ \end{matrix}\]

\(f\) is the length-ratio component where:

\[f = \frac{{\overline{L}}_{y - 1}}{L_{F = M}}\]

where \(\overline{L}\) is is the mean catch length above \(L_{F = M}\).

\(L_{F = M}\) is calculated as:

\[L_{F = M} = 0.75L_{c} + 0.25L_{\infty}\]

where \(L_{c}\) is the length where frequency is half that of the modal value (Figure 14), and L∞ is von Bertalanffy L∞.

\(b\) is the biomass safeguard and is used to reduce catch advice when index falls below trigger,

\[b = \min\left( 1,I_{y} - 1/I_{\text{trigger}} \right)\]

where \(I_{\text{trigger}}\) = \(i_{\text{loss}} \bullet 1.4\)

\(m\) is a multiplier based on stock growth. \(K\) for whiting could not be estimated reliably since the most recent data is from 1973 and hence, K from other areas was used instead. K for whiting is 0.38 and therefore \(m\) is 0.5 (0.32 <K < 0.45 yr-1).

Figure 14: Whiting. Length frequency distribution from catches. Red line is the length at first capture.

Analysis on the assessment and advice

Figure 15: Whiting. IS-SMB biomass index since 1985. The broken line shows Itrigger which is the lowest index value in the time series multiplied by 1.4.
  • f is the length-ratio component. The annual mean length from catches and the target reference length (Lc, the length where frequency is half that of the modal value * 0.75 + L∞ * 0.25, Table 2). \(HR_{MSY proxy}\) is calculated as \(HR_{proxy}\) for years when f>1 (Figure 16).
Figure 16: Whiting. Annual harvest rate proxy (HRproxy) for years for which suffucient data was available.

  • b is the biomass safeguard and is used to reduce catch advice when index falls below trigger. Iloss for whiting is based on the lowest biomass index and Itrigger is Iloss *1.4 (Figure 15). The biomass index this year is above Itrigger and hence, b is 1.

  • m is, as previously explained, the tuning parameter and for slow growing species (with von Bertalanffy 0.32 <K < 0.45 yr-1), m equals 0.5.

Application of the chr-rule

The assessment is based on the chr-rule for ICES category 3 data-limited stocks and is applied for the fishing year (2026/2027). The Icelandic spring trawl survey (IS-SMB) for individuals ≥40 cm was used as the spawning stock biomass index. The advice is according to Ay+1 = min(max(Iy \(HR_{MSY proxy}\),0.7 Ay),1.2 Ay) b m which result in advice 20% higher than last year’s advice as the stability clause is applied (Table 2).

Table 2: Whiting. Advice calculations.

Ay: Catch advice for 2025/2026

1 100

Biomass index

Latest index value (I2026)

18 239

Harvest rate proxy

HRMSY proxy: MSY proxy harvest rate (average of the ratio of catch to biomass index for the years for which f > 1, where f = Lmean / LF = M)

0.173

Biomass safeguard

Index trigger value (Itrigger = Iloss*1.4)

1 812

b: Index relative to trigger value, min(I2026 / Itrigger, 1)

1

Precautionary multiplier to maintain biomass above Blim with 95% probability

m: Multiplier (generic multiplier based on life history)

0.5

Advice calculation1)

1 580

Stability clause (+20% / -30% compared to Ay, only applied if b ≥ 1)2)

1

Catch advice for 2026/2027

1 320

% advice change3)

20

1) Ay+1 = Iy × HRMSY proxy × b × m, limited by stability clause

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.

Management

Whiting has not been subject to management such as TAC limitations, but advice has been given by the Marine and Freshwater Research Institute since 2019 (Table 3).

Table 3: Whiting. Recommended TAC, national TAC, and catches (tonnes).

Fishing year

Recommended TAC

National TAC

Total catch

2019/2020

836

607

2020/2021

1 003

844

2021/2022

1 137

826

2022/2023

1 091

1 263

2023/2024

1 309

722

2024/2025

1 571

694

2025/2026

1 100

References

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