TUSK in ICES Division 5.a and Subarea 14

Brosme brosme


Technical report
Published by

Marine and Freshwater Research Institute, Iceland

Published

6 June 2025

Key signals

  • Total stock biomass observed in the spring survey declined steadily from 1985 to 2001. It subsequently increased and remained at relatively high levels until 2020, when it reached its lowest point in the time series. Since then, biomass has increased again and is currently at the highest level observed.

  • Abundance of small tusk (<30 cm) in the, spring survey peaked in 2007, followed by a sharp decline until 2012. Since then, abundance has increased steadily and is now at its highest level in the time series. This increase is also evident in the length distribution from the SMB survey, where smaller tusk have become more frequent.

  • Spawning stock biomass (SSB) declined from 1981 to 2021 but has since shown a sharp increase.

  • Fishing mortality (F, ages 7–10) has been decreasing since 2010 and is now below the reference points FMGT, FPA and Flim since.

  • Recruitment has been increasing since 2011 and is currently at its highest observed level.

General information

Tusk, also commonly called cusk, is a slow-moving demersal species that lives solitary or in small aggregations in offshore stony or pebbly habitats, mainly at depths less than 400 m. It feeds on crustaceans, shellfish, and other demersal fish. In Icelandic waters it grows to sizes close to 100 cm and may attain ages close to 20 years, but age determination of individuals over 10 years old is highly uncertain.

The fishery

Landings trends

Tusk in 5.a is caught in a mixed longline fishery, conducted in order of importance by Icelandic, Faroese, and Norwegian boats. Between 90 and 370 Icelandic longliners report catches of tusk, but ~100 more vessels have small amounts of bycatch landings (Table 1). Far fewer gillnetters and trawlers participate in the fishery. The number of longliners reporting tusk catches has been continually decreasing in the last decade (Table 1). Most of tusk in 5.a, around 96% of catch, is caught by longlines, and this proportion has been relatively stable since 2000 (Table 1).

Figure 1: Tusk. Annual landings in ICES area 5.a and 14 since 1906
Table 1: Tusk. Number of Icelandic boats with tusk landings, catch by gear (tonnes) and total catches in ICES area 5.a since 2000.
Year nr. bottom trawl nr. nets nr. longlines Bottom trawls Net Longlines Other Total catch
2000 121 175 370 101 44 4 564 404 5 114
2001 108 224 350 87 63 3 248 1 439 4 838
2002 105 174 304 88 93 3 722 1 659 5 563
2003 97 148 305 65 41 3 941 1 549 5 598
2004 90 130 303 92 28 3 007 1 703 4 830
2005 88 101 324 116 19 3 398 1 510 5 044
2006 86 82 338 100 40 4 912 1 549 6 601
2007 74 65 308 104 38 5 834 1 560 7 537
2008 75 59 255 126 42 6 762 1 699 8 629
2009 75 65 239 115 72 6 757 1 524 8 469
2010 70 62 228 97 52 6 761 1 803 8 713
2011 63 54 221 72 24 5 742 1 862 7 701
2012 65 68 228 64 13 6 255 1 540 7 872
2013 66 43 233 76 15 4 911 1 300 6 302
2014 62 43 249 87 18 6 045 13 6 163
2015 55 32 228 71 7 4 745 13 4 835
2016 59 32 206 61 6 3 420 7 3 494
2017 52 31 180 48 5 2 481 6 2 540
2018 55 27 158 83 8 2 841 7 2 940
2019 49 23 154 103 7 3 323 11 3 445
2020 55 23 126 108 31 3 037 10 3 187
2021 51 18 123 112 12 2 649 6 2 779
2022 51 26 109 110 17 2 446 3 2 577
2023 53 32 94 91 10 2 940 5 3 047
2024 53 18 91 81 8 2 055 4 2 149

The main fishing grounds for tusk in 5.a as observed from logbooks are on the southeast, southwestern and western part of the Icelandic shelf (Figure 4 and Figure 5). The spatial distribution of catches in 5.a show a decreasing trend in the southeast until 2015, but this proportion has been increasing in the last 5 years (Figure 1 and Figure 5). The proportional catch in the northwest has also increased over the years. Most of the tusk caught in 5.a by Icelandic longliners is caught at depths less than 300 meters (Figure 3). Around 50–60% of tusk is caught on the southern and western parts of the shelf (Figure 3). Tusk in 14 is caught mainly as a bycatch by longliners and trawlers. The main area where tusk is caught in 14 is 63°–66°N and 32°–40°W (Figure 2).

Figure 2: Tusk. Distribution of catches in ICES area 14 from 1999-2023
Figure 3: Tusk. Depth distribution of catches in ICES area 5.a since 2000, as reported in logbooks by the Icelandic fleet. All gears combined.
Figure 4: Tusk. Catch distribution and proportions by region in ICES area 5.a since 2000, according to logbooks. All gears combined.
Figure 5: Tusk. Geographical distribution (tonnes) of the Icelandic longline fishery since 2004, as reported in logbooks by the Icelandic fleet.

Landings and discards

Total annual landings from ICES Division 5.a were 2149 tonnes in 2024 (Table 2). Since 2010, landings have steadily declined, dropping by 76%. This is contrary to the trend in landings from year 2000 to 2010 when annual landings gradually increased from approximately 5000 tonnes to 9000 tonnes (Figure 1). The foreign catch (mostly vessels from the Faroe Islands, but also from Norway) of tusk in Icelandic waters has always been considerable. Until 1990, between 40-70% of the total annual catch from ICES Division 5.a was caught by foreign vessels, mainly vessels from the Faroe Islands. This proportion has reduced since and has been 10-30% since 1991 (Table 2).

Landings in area 14 have always been low compared to 5.a, and before 2010 they rarely exceeded 100 t (Table 3). However, 1598 tonnes were caught in 2015, after which catches have been consistently substantial. In the fishing year 2015/2016, landings in 5.a were 900 tonnes and as the Icelandic TACs were relatively low during this period, this constituted over 25% of TAC. Landings data from section 14 reported by the Greenland Institute of Natural Resources also reflect this trend. In 2019, around 566 tonnes were caught in the 14.b mainly by Norwegian, Faroese and Greenlandic vessels (Table 3). This has however increased in 2024 to about 939 tonnes.

Discarding is banned in the Icelandic fishery. There is no available information on discarding of tusk in ICES area 14.

Table 2: Tusk. Nominal landings (tonnes) by country in ICES area 5.a since 1980
Year Iceland Faroe Islands Germany Norway United Kingdom Total landings
1980 3 109 2 873 0 928 0 6 910
1981 2 864 2 624 0 1 025 0 6 513
1982 2 801 2 410 0 666 0 5 877
1983 3 468 4 046 0 772 0 8 286
1984 3 430 2 008 0 254 0 5 692
1985 3 064 1 885 0 111 0 5 060
1986 2 549 2 811 0 21 0 5 381
1987 2 987 2 638 0 19 0 5 644
1988 3 087 3 757 0 20 0 6 864
1989 3 158 3 908 0 10 0 7 076
1990 4 821 2 475 0 0 0 7 296
1991 6 449 2 286 0 0 0 8 735
1992 6 432 1 567 0 0 0 7 999
1993 4 086 1 333 0 0 0 5 419
1994 4 065 1 217 0 0 0 5 282
1995 5 151 1 168 1 0 0 6 320
1996 5 548 907 1 3 0 6 470
1997 4 816 579 0 0 0 5 395
1998 4 130 1 080 1 0 0 5 211
1999 5 821 1 041 2 391 2 7 257
2000 4 727 10 0 374 3 5 114
2001 3 397 1 150 1 285 5 4 838
2002 3 910 1 279 0 372 2 5 563
2003 4 024 1 198 1 373 2 5 598
2004 3 135 1 478 1 214 2 4 830
2005 3 539 1 157 4 303 41 5 044
2006 5 054 1 244 2 299 2 6 601
2007 5 987 1 250 0 300 1 7 538
2008 6 934 1 398 0 298 0 8 630
2009 6 953 1 516 0 210 0 8 679
2010 6 919 1 794 0 263 0 8 976
2011 5 847 1 655 0 198 0 7 700
2012 6 344 1 310 0 217 0 7 871
2013 4 992 1 118 0 192 0 6 302
2014 5 057 681 0 425 0 6 163
2015 4 059 578 0 198 0 4 835
2016 2 704 488 0 302 0 3 494
2017 1 887 438 0 216 0 2 541
2018 2 160 454 0 326 0 2 940
2019 2 622 506 0 316 0 3 444
2020 2 380 536 0 271 0 3 187
2021 2 109 283 0 388 0 2 780
2022 1 956 264 0 357 0 2 577
2023 2 414 322 0 311 0 3 047
2024 1 539 287 0 123 0 2 148
Table 3: Tusk. Nominal landings (tonnes) by country in ICES area 14 since 1978.
Year Faroe Islands Norway Iceland Russia Spain Greenland Germany United kingdom Total landings
1978 0 38 0 0 0 0 47 0 85
1979 0 0 0 0 0 0 27 0 27
1980 0 0 0 0 0 0 13 0 13
1981 110 0 0 0 0 0 10 0 120
1982 0 0 0 0 0 0 10 0 10
1983 74 0 0 0 0 0 11 0 85
1984 0 58 0 0 0 0 5 0 63
1985 0 0 0 0 0 0 4 0 4
1986 33 0 0 0 0 0 2 0 35
1987 13 0 0 0 0 0 2 0 15
1988 19 0 0 0 0 0 2 0 21
1989 13 0 0 0 0 0 1 0 14
1990 0 7 0 0 0 0 2 0 9
1991 0 68 0 0 0 0 2 1 71
1992 0 120 3 0 0 0 0 0 123
1993 0 39 1 0 0 0 0 0 40
1994 0 16 0 0 0 0 0 0 16
1995 0 30 0 0 0 0 0 0 30
1996 0 157 0 0 0 0 0 0 157
1997 0 9 10 0 0 0 0 0 19
1998 0 12 0 0 0 0 0 0 12
1999 0 8 0 0 0 0 0 0 8
2000 0 11 11 0 3 0 0 0 25
2001 3 69 20 0 0 0 0 0 92
2002 4 30 86 0 0 0 0 0 120
2003 0 88 2 0 0 0 0 0 90
2004 0 40 0 0 0 0 0 0 40
2005 7 41 0 8 0 0 0 0 56
2006 3 19 0 51 0 0 0 0 73
2007 0 40 0 6 0 0 0 0 46
2008 0 7 0 0 0 33 0 0 40
2009 12 5 0 11 0 15 0 0 43
2010 7 5 0 0 0 0 0 0 12
2011 20 24 131 0 0 0 0 0 175
2012 33 46 174 0 0 0 0 0 253
2013 2 24 401 0 0 0 0 0 427
2014 145 35 0 0 0 74 0 0 254
2015 759 55 0 0 0 784 0 0 1 598
2016 243 178 0 0 0 182 3 0 606
2017 281 141 0 0 0 358 0 0 780
2018 345 228 0 0 0 108 0 0 681
2019 41 458 0 0 0 66 1 0 566
2020 64 114 0 0 0 45 2 0 225
2021 260 380 0 0 0 59 2 0 701
2022 35 558 0 0 0 87 1 0 681
2023 170 479 0 0 0 115 0 0 764
2024 287 477 0 0 0 174 1 0 939

Data available

In general sampling is considered appropriate from commercial catches from the main gear (longlines), although the quantity of samples has decreased substantially in the last decade (Table 5). The sampling does seem to cover the spatial distribution of catches for longlines and trawls. Similarly, sampling does seem to follow the temporal distribution of catches (ICES (2012)). The sampling coverage in 2024 is shown in Figure 6.

Figure 6: Tusk. Ratio of catch samples by month (bars) compared with proportion landings by month (black line) split by year and main gear types. Numbers above the bars indicate number of samples by year, month and gear from commercial catches of Icelandic vessels fishing in ICES area 5.a from 2021-2024

Length compositions

An overview of available length measurements from 5.a is given in Table 4. Most of the measurements are from longlines; number of available length measurements increased in 2007 from around 5000 to around 12000 and were close to that until 2015 when they decreased and in 2024, the number of length measurements from longlines were 1748. Length distributions from the longline fishery is shown in Figure 7.

No length composition data from commercial catches in Greenlandic waters are available.

Figure 7: Tusk. Length distributions from Icelandic commercial longline catches.
Table 4: Tusk. Number of available length measurements from the Icelandic commercial catches in ICES area 5.a since 2000.
Year Bottom trawl Long lines Danish seine Gillnets
2000 0 2 995 0 0
2001 0 3 097 0 0
2002 0 2 843 0 0
2003 0 8 444 0 0
2004 150 3 809 0 0
2005 21 5 820 0 0
2006 472 4 861 0 0
2007 150 11 936 0 167
2008 0 20 963 0 0
2009 0 21 451 0 0
2010 0 9 084 0 0
2011 0 8 159 0 0
2012 150 11 867 0 0
2013 0 6 469 150 0
2014 0 11 748 0 0
2015 0 4 821 0 0
2016 0 4 844 0 0
2017 0 1 710 0 0
2018 0 2 781 0 0
2019 0 2 952 0 0
2020 1 2 336 0 0
2021 0 1 499 0 0
2022 83 682 0 0
2023 0 2 671 0 0
2024 120 1 748 0 0

Age composition

Table 5 gives an overview of otolith sampling intensity by gear types from 2008 to 2024 in 5.a. Since 2010, considerable effort has been put into ageing tusk otoliths, so now aged otoliths are available from 1984–1995, 2008–2024. The age data are used as input for the SAM assessment. It is expected that the effort in ageing of tusk will continue. Catch at age per year is shown in Figure 8 and by cohort per year in Figure 9.

Figure 8: Tusk. Catch at age from the commercial fishery in ICES area 5.a. Bar size is indicative of the catch in numbers and bars are coloured by cohort.
Figure 9: Tusk. Catch at age from the commercial fishery in ICES area 5.a since 1981. Biomass (tonnes) caught by year and age; bars are coloured by cohort.
Table 5: Tusk. Number of available otoliths from Icelandic commercial catches and the Icelandic Spring survey (SMB) and the number of aged otoliths in ICES area 5.a since 2008.
Year No. samples (Bottom trawl) No. samples (Long line) No. otoliths (Bottom trawl) No.otoliths (Long line) No. samples (Survey) No. otoliths (Survey)
2008 0 110 0 1 600 287 489
2009 0 108 0 1 350 286 453
2010 0 58 0 1 449 248 378
2011 0 43 0 1 400 274 738
2012 1 70 50 1 700 286 771
2013 0 35 0 1 100 278 744
2014 0 62 0 620 243 585
2015 0 35 0 555 263 614
2016 0 28 0 290 261 689
2017 0 14 0 160 247 580
2018 0 23 0 180 251 560
2019 0 29 0 330 252 721
2020 1 18 0 290 251 657
2021 0 13 0 270 278 827
2022 1 8 20 160 315 906
2023 0 22 0 355 305 905
2024 1 13 20 200 305 954

Catch weight at age

Weight-at-age per cohort from catch in 5.a is shown in Figure 10. No data are available from 14. Catch weights of three year old is stable and around the average, whereas the other age groups show more variability between years. The three oldest year classes are the most common in the catch, and recently, younger tusk has become less common in catch (?@fig-rowthplot). No data are available from area 14.

Figure 10: Tusk. Mean weight at age in the catch from the commercial fishery in ICES area 5.a. Bars are coloured by cohort.

Icelandic survey data (ICES Subarea 27.5a)

Information on abundance and biological parameters from tusk in Icelandic waters is available from the Icelandic groundfish survey in the spring (SMB) and the Icelandic autumn survey (SMH). In addition, a gillnet survey is conducted in areas closer inshore every April during cod spawning periods, designed to sample the cod spawning stock. A detailed description of the Icelandic spring, autumn groundfish surveys and the gillnet surveys are given in the stock annex (ICES 2023). The Icelandic spring groundfish survey, which has been conducted annually in March since 1985, covers the most important distribution area of the tusk fishery. In the years between 1996 and 2006 the Icelandic spring survey did not cover the Faroe ridge area. A considerable proportion of the catches, roughly 20%, in the survey is caught in that area, although variable between length groups. To allow for consistency within the indices the values of the indices were scaled according the median proportion caught in the area. In addition, the autumn survey commenced in 1996 and expanded in 2000; however, a full autumn survey was not conducted in 2011 and therefore the results for 2011 are not presented. A detailed description of the Icelandic spring and autumn groundfish surveys is given in the Stock Annex (ICES (2017b)). Figure 11 shows a recruitment index and the trends in various biomass indices. Length distribution from the autumn and spring survey is shown in Figure 13 and the survey index at age from the spring survey in Figure 14. Since 2014, the survey indices of younger tusk have been increasing. This is also apparent in the length distribution from the spring survey, where smaller tusk have become more frequent.

Figure 11: Tusk. a) Total biomass indices, b) biomass indices larger than and including 40 cm, c) biomass indices larger than and including 60 cm and d) abundance indices smaller than and including 30 cm. The lines with shaded areas show the spring survey (SMB) index from 1985 and the points with the vertical lines show the autumn survey (SMH) from 1996. The shaded area and vertical lines indicate +/- standard error. The dark green line without a shaded area is the index excluding the Iceland-Faroe Ridge.
Figure 12: Tusk. Estimated annual survey biomass in the spring survey (SMB) by year since 1985, and the autumn survey since 1996 from different parts of the continental shelf (upper figure) and as proportions of the total (lower figure)
Figure 13: Tusk. Length distributions from the spring survey (SMB) since 1985 and the autumn survey (SMH) since 1996.
Figure 14: Tusk. Age disaggregated indices in the autumn survey (SMH) since 1996 and the spring survey (SMB) since 1985. Bar colours indicate cohorts. Note different scales on y-axes.

Stock weight at age

Mean stock weight at age per cohort in SMB is shown in Figure 15. The values are obtained from the SMB in March and are also used as mean weight at age in the spawning stock for the assessment. Mean weight of the oldest year classes gradually increased since the early 2000s, whereas the mean weight at age of younger tusk is more variable between years.

Figure 15: Tusk. Stock weights from the spring survey (SMB) in Icelandic waters since 1985. Bars are coloured by cohort

Stock maturity at age

Maturity at age data is taken from SMH and calculated based on maturity at length for each year and length distributions of fish assigned to each age. From 1994 to 2000, the proportion mature at age increased gradually in age groups 5 to 10, but steadily declined after until the year 2015. Since then, there has been an upward trend in the proportion of individuals reaching maturity at older ages, with maturity approaching the mean (Figure 16 and Figure 17). The SMB data is not used because maturation patterns appeared to occur at larger fish and differed between sexes.

Figure 16: Tusk. Maturity at age in the autumn survey (SMH). Bars are coloured by cohort. The values are used to calculate the spawning stock.
Figure 17: Tusk. Proportion mature at length from the autumn survey (SMH).

Other surveys

German survey data (ICES Subarea 27.14)

The German groundfish survey was started in 1982 and is conducted in autumn. It is primarily designed for cod but covers the entire groundfish fauna down to 400 m. The survey is designed as a stratified random survey; the hauls are allocated to strata off West and East Greenland both according to the area and the mean historical cod abundance at equal weights. Towing time was 30 minutes at 4.5 kn. (Ratz, 1999). Data from the German survey in 14 were available at the meeting up to 2015. The trend in the German survey catches is similar to those observed in surveys in 5.a. It should, however, be noted that the data presented in Figure 18 is based on total number caught each year so it can’t be used directly as an index from East Greenland. Length distributions from the survey in recent years are shown in Figure 19.

Figure 18: Tusk. Biomass and abundance estimates from the Walter Herwig survey in ICES area 14 from 1981 to 2015. The data display the total number caught (abundance) which is then converted to biomass.
Figure 19: Tusk. Length distributions from the Walter Herwig survey in ICES area 14 from 1991 to 2015.

Greenland survey data (ICES Subarea 27.14)

The Greenland Institute of Natural Resources conducted a stratified bottom trawl survey in East Greenland (ICES 14b) from 1998 to 2016 at depths between 400 to 1500 m (ICES 2019:WD05). Survey results for tusk show a highly variable but increasing trend over recent years, so results from this survey will be monitored after it resumes in the future as a potential biomass index to be included in the tusk assessment.

Data analyses

Landings data

There have been notable changes in the number of boats or the composition of the fleet participating in the tusk fishery in area 5.a since the year 2000 (Table 1). Catches decreased from around 9000 tons in 2010 to 2149 tonnes in 2024. This decrease is mainly because of reductions in landings by the Icelandic long line fleet, and to a lesser extent, Faroese and Norwegian landings (Table 2 and Table 3). This has resulted in less overshoot of landings relative to set TAC.

Length data

There are no marked changes in the length compositions since 2000 (Figure 7). Length distributions from SMB show a distinct large cohort, or series of consecutive cohorts, appearing in 2014, growing through time, and just beginning to reach fished sizes approximately two years ago. This recruitment peak appears to follow a recruitment low that can also be traced through the length distribution from 2014 and can still be observed this year as slightly lower-than-average frequencies of tusk in the 45-50 cm range. According to the available length distributions and information on maturity only around 29% of catches in abundance and 44% in biomass are mature. The reason for this is unknown but given the lack of distinctive cohort structure in the data the first explanation might be a lack of consistency in ageing. Also, tusk have experienced a reduction in fishing mortality over the latter half of this range. Reasons such as difference in sampling, temporal or spatial are highly unlikely.

Survey index data

At WGDEEP 2011 the Iceland-Faroe Ridge was included in the survey index when presenting the results from SMB for tusk in area 5.a. The total biomass index and the biomass index for tusk larger than 40 cm (reference biomass) decreased substantially until the year 2000, but increased again until around the year 2011. th eindex decreased again until 2020 but has since been increasing and is now the highest in the time-series (Figure 8). The same holds for the index of tusk larger than 60 cm (spawning–stock biomass index), which has been increasing since 1995. The index of juvenile abundance (<30 cm) decreased by a factor of six between the 2005 survey when it peaked and the 2013 survey when it was at its lowest observed value. Since 2013 juvenile index has increased and is now at a similar level as in 2011. The index excluding the Iceland-Faroe Ridge shows similar trends as described above. The results from the shorter autumn survey are similar to those observed from SMB except for the juvenile abundance index that is more or less at a constant level compared to SMB juvenile index. Due to a labour strike, the autumn survey did not take place in 2011. When looking at the spatial distribution from SMB, around 25% of the index is from the SE area. However only around 4% of the catches are caught in this area (Figure 4 and Figure 5). The change in juvenile abundance between 2006 and recent years can be seen in Figure 8.

Catch, effort and research vessel data

The CPUE estimates of tusk in 5.a are not considered representative of stock abundance.

CPUE estimations have not been attempted on available data from 14.

Analytical assessment using SAM

From 2010-2021, a Gadget model (Globally applicable Area Disaggregated General Ecosystem Toolbox, see www.hafro.is/gadget) was used for the assessment of tusk in 5.a (See stock annex for details, ICES 2023). In 2022, Tusk in 5.a and 14 was re-assessed as the previously benchmarked Gadget model had begun to show great instability in retrospective patterns in recent years. As a part of a Harvest Control Evaluation requested by Iceland, the stock was benchmarked in the year 2022 (WKICEMSE 2022b) which resulted in changes in the assessment method and updated reference points. Model setup and settings are described in the stock annex (ICES 2023).

Data used by the assessment and model settings

Data used for tuning and the model configuration are given in the stock annex (ICES 2023).

Model fit

Model results are shown in Figure 21 The model fit to survey indices and catch are shown in Figure 20. Generally, the model closely follows SMB data, which are in good agreeance. The SMH and catch are noisier but generally follows the same pattern. Fits to the SMN (age 10 abundance) are much noisier. An overview of model parameter estimates are shown in Figure 25.

Figure 20: Tusk. Model fit to indices from the spring survey, autumn survey, gillnet survey and landings. Black dots are observed values and the black line is the model fit.
Figure 21: Tusk. Model results of population dynamics overview: estimated catch, average fishing mortality over ages 7-10 (Fbar), recruitment (age 1), and spawning stock biomass (SSB). Catch and fbar values in 2025 are projections.

Model results

Estimated spawning stock biomass (SSB) displays a declining trend from 1979 to 1995, although prior to 1985 the model is informed by very little data, so uncertainty is high. SSB in the period 1995-2015 was steady, with a gradual decline thereafter that continued until 2021, when biomass levels began increasing again. This pattern is likely due to a distinctive low point in recruitment in 2011-2012, which has since then increased to relatively high levels. Therefore, given moderate fishing levels, spawning stock biomass is expected to increase over the next several years due to large cohorts being recruited into the fishery. The previous peak in recruitment (2004-2005) likely did not increase spawning stock biomass levels substantially during years 2008-2010 due to higher fishing rates and catch values during those years, when these fish would have been entering the fishery (Figure 21).

Retrospective analysis

The results of an analytical retrospective analysis are presented (Figure 22). The analysis indicates generally consistent model results over the 5-year peel. Mohn’s ρ was estimated to be -0.008 for SSB, 0.192 for F, and -0.159 for recruitment. Recruitment indices generally tend to be uncertain as there are few repeated observations at larger sizes with which this influence can be tempered. However, the good fit to survey indices at age 1, (Figure 20), suggests that recent recruitment estimates from this peak are reliable. In addition, a peak in these sizes of tusk followed by a sharp decline in 2020 are reflected in length distribution data as a rather large but steep peak in proportions of fish that have begun to shift right (to larger sizes) with no obvious new peaks of small sizes taking its place (Figure 8). Therefore, it is likely that the increase in biomass observed this year will continue in the next year or so.

Figure 22: Tusk. Retrospective plots illustrating stability in model estimates over a 5-year “peel” in data. Results of spawning stock biomass, fishing mortality F, and recruitment (age 1) are shown as well as the mohn´s rho values

Observation and process residuals show slight trends in autocorrelation and some blocks of time where the model was consistently over- or underestimating the model (Figure 23 and Figure 24). However, a better model configuration could not be found at the last benchmark that would remove these patterns, and similar model configurations gave similar model results (WKICEMP, ICES 2022c). Process variance is therefore rather high in this model, indicating high uncertainty in true population dynamics, due to greater uncertainty in input data.

Figure 23: Tusk. Observation error residuals of the SAM model.
Figure 24: Tusk. Process error residuals of the SAM model.
Figure 25: Tusk. Illustration of estimated model parameters.
Figure 26: Tusk. Comparsion of the modelled survey indices (solid lines) and survey indices (dots).

Reference points

As part of the WKICEMP 2022 HCR evaluations (ICES 2022c), the following reference points were defined.

Table 6: Tusk. Reference points adopted from the last benchmark in 2022.
Framework Reference_point Value Technical_basis
MSY Approach MSY Btrigger 4800 Bpa
FMSY 0.23 F that produces MSY in the long term
Precautionary Approach Blim 3400 Bloss (SSB in 1993)
Bpa 4800 Blim x e1.645 * σB
Flim 0.44 Fishing mortality that in stochastic equilibrium will result in median SSB at Blim.
Fpa 0.23 Maximum F at which the probability of SSB falling below Blim is <5%
Management plan MGT Btrigger 4800 According to the harvest control rule
FMGT 0.23 According to the harvest control rule

The harvest control rule (HCR) for the Icelandic Ling fishery, which sets a TAC for the fishing year y/y+1 (September 1 of year y to August 31 of year y+1) based on a fishing mortality FMGT of 0.30 applied to ages 8 to 11 modified by the ratio SSB\(_{y}\)/MGT B\(_{\text{trigger}}\) when SSB\(_{y}\) < MGT B\(_{\text{trigger}}\), maintains a high yield while being precautionary as it results in lower than 5% probability of SSB < B\(_{\lim}\) in the medium and long term. WKICEMSE 2022 concluded that the HCR was precautionary and in conformity with the ICES MSY approach (WKICEMSE 2022b).

Management

The Icelandic Ministry Industries is responsible for management of the Icelandic fisheries and implementation of legislation. Tusk was included in the ITQ system in the 2001/2002 quota year and as such subjected to TAC limitations. At the beginning, the TAC was set as recommended by MFRI but thereafter had often been set higher than the advice. One reason is that no formal harvest advisory rule existed for this stock. Up until the fishing year 2011/2012, the landings, by quota year had always exceeded the advised and set TAC by 30-40%. However, since then the overshoot in landings has decreased substantially, apart from 2014/2015 when the overshoot was 34%. In recent years the TACs were not filled, until the past two years when the TAC has been exceptionally low (Table 7).

The reasons for the large difference between annual landings and both advised and set TACs are threefold: 1) It is possible to transfer unfished quota between fishing years; 2) It is possible to convert quota shares in one species to another; 3) The national TAC is only allocated to Icelandic vessels. All foreign catches are therefore outside the quota system. However, in recent years managers have to some extent taken into account the foreign catches when setting the national TAC (see below).

There are bilateral agreements between Iceland, Norway and the Faroe Islands (revised annually) related to fishing activity of foreign vessels in restricted areas within the Icelandic EEZ. Faroese longliners are allowed to fish for demersal species in the Icelandic EEZ and since 2011, around 15 Faroese longliners have operated in Icelandic waters, fishing mainly cod, haddock, ling, and tusk. The tusk advice given by MFRI and ICES for each quota year is, however, for all catches, including foreign catches.

Figure 27 shows the net transfers in the Icelandic ITQ-system. During the 2005/2006–2010/2011 fishing years there was a net transfer of other species quota being converted to tusk quota, this however reversed during the following three fishing years. In the 2015/2016 and 2016/2017 fishing years there was again a small net transfer of other species being changed to tusk quota. In the last four out of five fishing years, 2017/2018-2019/2020 fishing years, net transfers were negative again with tusk quota being converted to other species, while 2020/2021 and 2021/2022 shows an overshoot of the quota. In 2023/2024, tusk quota was transferred to other species (Figure 27).

Table 7: Tusk. Recommended TAC, national TAC for Iceland, and catches.
Fishing year MFRI advice National TAC Catch Iceland Catch other Total catch
2010/2011 6000 6000 6235 1898 6235
2011/2012 6900 6900 5983 1606 5983
2012/2013 6700 6700 5555 1336 5569
2013/2014 6300 6300 4850 1360 5438
2014/2015 4000 4000 4136 1304 5440
2015/2016 3440 3440 3221 900 4121
2016/2017 3780 3780 1689 729 2418
2017/2018 4370 4370 2200 885 3085
2018/2019 3776 3776 2453 778 3231
2019/2020 3856 3856 2460 781 3241
2020/2021 2289 2289 2192 757 2949
2021/2022 2172 2172 1918 503 2421
2022/2023 4464 4464 2421 640 3061
2023/2024 5139 5139 1592 784 2376
2024/2025 5914 5914
2025/2026 7451
Figure 27: Tusk. Net transfer of quota in the Icelandic ITQ system by fishing year since fishing year 2001/2002. Between species (upper): Positive values indicate a transfer of other species to tusk, but negative values indicate a transfer of tusk quota to other species. Between years (lower): Net transfer of quota for a given fishing year (may include unused quota). Displayed both in tonnes and as proportion on TAC.

Management considerations

Catches in area 14.b, and now 14.a also, increased from less than 100 tonnes annually from 1978 to 2014, to 1600 tonnses in 2015. Catches reduced after 2015 but have ranged from 225-934 tonnes since. The increase in catch during the last decade compared to previous 35 years is of concern. However, the signs from commercial catch data and surveys indicate that the total biomass of tusk in 5.a is stable. This is confirmed in the assessment. Recruitment in 5.a sjowed increasing levels from a low in 2011. A reduction in fishing mortality since 2010 has also led to harvestable biomass and SSB that seem to be either stable or slowly increasing. Due to the selectivity of the longline fleet catching tusk in 5.a and the species relatively slow maturation rate, a large proportion of the catches is immature (60% in biomass, 70% in abundance). The spatial distribution of the fishery in relation to the spatial distribution of tusk in 5.a as observed in SMB may result in decreased catch rates and local depletions of tusk in the main fishing areas. Tusk is a slow growing late maturing species, therefore closures of known spawning areas should be maintained and expanded if needed. Similarly, closed areas to longline fishing where there is high juvenile abundance should also be maintained and expanded if needed.

Figure 28: Tusk. Comparison of the total allowable catch, adviced catch and total catch within the Icelandic EEZ.

References

ICES. 2011. “Report of the Working Group on the Biology and Assessment of Deep-Sea Fisheries Resources (WGDEEP), 2 March–8 March, 2011, Copenhagen, Denmark. ICES Cm 2011/Acom:17.” International Council for the Exploration of the Seas; ICES publishing.

2012. “Report of the Working Group on the Biology and Assessment of Deep-Sea Fisheries Resources (WGDEEP), 28 March–5 April, 2012, Copenhagen, Denmark. ICES Cm 2012/Acom:17.” International Council for the Exploration of the Seas; ICES publishing.

2017. “Report of the Workshop on Evaluation of the Adopted Harvest Control Rules for Icelandic Summer Spawning Herring, Tusk and Tusk (WKICEMSE), 21–25 April 2017, Copenhagen, Denmark. ICES CM 2017/ACOM:45.” International Council for the Exploration of the Seas; ICES publishing.

2022a. “11.2 Icelandic Waters ecoregion – Fisheries overview.” International Council for the Exploration of the Seas; ICES publishing. https://doi.org/10.17895/ices.advice.21487635.v1

2022b. Iceland request for evaluation of a harvest control rule for tusk in Icelandic waters. In Report of the ICES Advisory Committee, 2022. ICES Advice 2022, sr.2022.6d, https://doi.org/10.17895/ices.advice.19625823

2022c. Workshop on the evaluation of assessments and management plans for Tusk, tusk, plaice and Atlantic wolffish in Icelandic waters (WKICEMP). ICES Scientific Reports. Report. https://doi.org/10.17895/ices.pub.19663971.v1

  1. Stock annex: Tusk (Brosme brosme) in Subarea 14 and Division 5.a (East Greenland, and Iceland grounds). ICES Stock Annexes. Report. https://doi.org/10.17895/ices.pub.23599668.v1