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 150 and 240 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 past few years (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).
Year | nr. bottom trawl | nr. nets | nr. Longlines | Bottom trawls | Net | Longlines | Other | Total catch |
---|---|---|---|---|---|---|---|---|
2000 | 120 | 175 | 370 | 100 | 44 | 4564 | 29 | 5114 |
2001 | 108 | 224 | 350 | 87 | 63 | 3248 | 24 | 4838 |
2002 | 103 | 174 | 304 | 88 | 93 | 3722 | 17 | 5563 |
2003 | 97 | 148 | 305 | 65 | 41 | 3941 | 11 | 5598 |
2004 | 90 | 129 | 303 | 92 | 28 | 3007 | 8 | 4830 |
2005 | 87 | 101 | 324 | 115 | 19 | 3398 | 7 | 5044 |
2006 | 85 | 82 | 338 | 100 | 40 | 4912 | 7 | 6601 |
2007 | 74 | 65 | 308 | 104 | 38 | 5834 | 11 | 7537 |
2008 | 75 | 59 | 255 | 126 | 42 | 6762 | 7 | 8629 |
2009 | 75 | 65 | 239 | 115 | 72 | 6757 | 9 | 8679 |
2010 | 70 | 62 | 228 | 97 | 52 | 6761 | 9 | 8976 |
2011 | 63 | 54 | 221 | 72 | 24 | 5742 | 9 | 7701 |
2012 | 65 | 68 | 228 | 64 | 13 | 6255 | 13 | 7872 |
2013 | 66 | 43 | 233 | 76 | 15 | 4911 | 12 | 6302 |
2014 | 62 | 43 | 249 | 87 | 18 | 6045 | 12 | 6163 |
2015 | 55 | 32 | 228 | 71 | 7 | 4745 | 13 | 4835 |
2016 | 59 | 32 | 206 | 61 | 6 | 3420 | 7 | 3494 |
2017 | 52 | 31 | 180 | 48 | 5 | 2481 | 5 | 2540 |
2018 | 55 | 27 | 158 | 83 | 8 | 2840 | 4 | 2940 |
2019 | 49 | 23 | 154 | 103 | 7 | 3323 | 9 | 3445 |
2020 | 55 | 23 | 126 | 108 | 31 | 3037 | 9 | 3187 |
2021 | 51 | 18 | 123 | 112 | 12 | 2649 | 5 | 2779 |
2022 | 51 | 26 | 109 | 110 | 17 | 2446 | 4 | 2577 |
2023 | 53 | 32 | 94 | 91 | 10 | 2939 | 5 | 3046 |
Most of the tusk caught in 5.a by Icelandic longliners is caught at depths less than 300 meters (Figure 2). 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 3 and Figure 4). The spatial distribution of catches in 5.a according to logbook entries shows a decreasing trend in the southeast until 2015, but this proportion has been increasing in the last 5 years (Figure 1 and Figure 4). The proportional catch in the northwest has also increased over the years. 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, well away from the Icelandic EEZ.
Landings and discards
Total annual landings from ICES Division 5.a were 3046 tonnes in 2023 (Table 2), signifying a continuous decrease in landings from 2010. This is contrary to the trend in landings from year 2000 in which the annual landings gradually increased in 5.a to around 9000 tonnes in 2010 (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 1).
Landings in area 14 have always been low compared to 5.a, rarely exceeding 100 t (Table 3). However, 1598 tonnes were caught in 2015, after which catches have been consistently substantial. Catch data from section 14 reported by the Greenland Institute of Natural Resources (WGDEEP, 2019:WD06) also reflect this trend. Around 566 tonnes in 2019 were caught in the 14.b mainly by Norwegian, Faroese and Greenlandic vessels (Table 3). This has however increased in 2023 to about 1528 tonnes. As the Icelandic TACs were relatively low during this period, this constituted over 25% of the annual catch.
Discarding is banned in the Icelandic fishery. There is no available information on discarding of tusk.
Year | Faroe Islands | Germany | Iceland | Norway | UK | Total catch |
---|---|---|---|---|---|---|
1980 | 2873 | 0 | 3089 | 928 | 0 | 6890 |
1981 | 2624 | 0 | 2827 | 1025 | 0 | 6476 |
1982 | 2410 | 0 | 2804 | 666 | 0 | 5880 |
1983 | 4046 | 0 | 3469 | 772 | 0 | 8287 |
1984 | 2008 | 0 | 3430 | 254 | 0 | 5692 |
1985 | 1885 | 0 | 3068 | 111 | 0 | 5064 |
1986 | 2811 | 0 | 2549 | 21 | 0 | 5381 |
1987 | 2638 | 0 | 2984 | 19 | 0 | 5641 |
1988 | 3757 | 0 | 3078 | 20 | 0 | 6855 |
1989 | 3908 | 0 | 3131 | 10 | 0 | 7049 |
1990 | 2475 | 0 | 4813 | 0 | 0 | 7288 |
1991 | 2286 | 0 | 6439 | 0 | 0 | 8725 |
1992 | 1567 | 0 | 6437 | 0 | 0 | 8004 |
1993 | 1329 | 0 | 4746 | 0 | 0 | 6075 |
1994 | 1212 | 0 | 4612 | 0 | 0 | 5824 |
1995 | 979 | 1 | 5245 | 0 | 0 | 6225 |
1996 | 872 | 1 | 5226 | 3 | 0 | 6102 |
1997 | 575 | 0 | 4819 | 0 | 0 | 5394 |
1998 | 1052 | 1 | 4118 | 0 | 0 | 5171 |
1999 | 1035 | 2 | 5794 | 391 | 2 | 7224 |
2000 | 1154 | 0 | 4714 | 374 | 2 | 6244 |
2001 | 1125 | 1 | 3392 | 285 | 5 | 4808 |
2002 | 1269 | 0 | 3840 | 372 | 2 | 5483 |
2003 | 1163 | 1 | 4028 | 373 | 2 | 5567 |
2004 | 1478 | 1 | 3126 | 214 | 2 | 4821 |
2005 | 1157 | 3 | 3539 | 303 | 41 | 5043 |
2006 | 1239 | 2 | 5054 | 299 | 2 | 6596 |
2007 | 1250 | 0 | 5984 | 300 | 1 | 7535 |
2008 | 959 | 0 | 6932 | 284 | 0 | 8175 |
2009 | 997 | 0 | 6955 | 300 | 0 | 8252 |
2010 | 1794 | 0 | 6919 | 263 | 0 | 8976 |
2011 | 1347 | 0 | 5845 | 198 | 0 | 7390 |
2012 | 1203 | 0 | 6341 | 217 | 0 | 7761 |
2013 | 1092 | 0 | 4973 | 192 | 0 | 6257 |
2014 | 728 | 0 | 4995 | 306 | 0 | 6029 |
2015 | 625 | 0 | 4000 | 198 | 0 | 4823 |
2016 | 543 | 0 | 2649 | 302 | 0 | 3494 |
2017 | 492 | 0 | 1833 | 216 | 0 | 2540 |
2018 | 517 | 0 | 2097 | 326 | 0 | 2940 |
2019 | 549 | 0 | 2579 | 316 | 0 | 3444 |
2020 | 558 | 0 | 2590 | 272 | 0 | 3420 |
2021 | 341 | 0 | 2049 | 389 | 0 | 2780 |
2022 | 288 | 0 | 1932 | 357 | 0 | 2577 |
2023 | 336 | 0 | 2399 | 311 | 0 | 3046 |
Year | Faroe Islands | Norway | Iceland | Russia | Spain | Greenland | Germany | United kingdom | total |
---|---|---|---|---|---|---|---|---|---|
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 | 1598 |
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 |
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 recent years. 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 2023 is shown in Figure 5.
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 2016 when they decreased and in 2023, the number of length measurements from longlines were 2671. Length distributions from the longline fishery is shown in Figure 6.
No length composition data from commercial catches in Greenlandic waters are available.
Year | Bottom trawl | Demersal seine | Gill nets | Longlines | Other |
---|---|---|---|---|---|
2000 | 0 | 0 | 0 | 2995 | 0 |
2001 | 0 | 0 | 0 | 3097 | 151 |
2002 | 0 | 0 | 0 | 2843 | 0 |
2003 | 0 | 0 | 0 | 8444 | 0 |
2004 | 150 | 0 | 0 | 3809 | 0 |
2005 | 21 | 0 | 0 | 5820 | 0 |
2006 | 472 | 0 | 0 | 4861 | 0 |
2007 | 150 | 0 | 167 | 11936 | 0 |
2008 | 0 | 0 | 0 | 20963 | 0 |
2009 | 0 | 0 | 0 | 21451 | 0 |
2010 | 0 | 0 | 0 | 9084 | 0 |
2011 | 0 | 0 | 0 | 8158 | 0 |
2012 | 150 | 0 | 0 | 11867 | 0 |
2013 | 0 | 150 | 0 | 6469 | 0 |
2014 | 0 | 0 | 0 | 11748 | 0 |
2015 | 0 | 0 | 0 | 4821 | 0 |
2016 | 0 | 0 | 0 | 4844 | 0 |
2017 | 0 | 0 | 0 | 1710 | 0 |
2018 | 0 | 0 | 0 | 2781 | 0 |
2019 | 0 | 0 | 0 | 2952 | 0 |
2020 | 1 | 0 | 0 | 2336 | 0 |
2021 | 0 | 0 | 0 | 1499 | 26 |
2022 | 83 | 0 | 0 | 682 | 461 |
2023 | 0 | 0 | 0 | 2671 | 0 |
Age composition
Table 5 gives an overview of otolith sampling intensity by gear types from 2008 to 2023 in 5.a. Since 2010, considerable effort has been put into ageing tusk otoliths, so now aged otoliths are available from 1984–1995, 2008–2023. 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 is shown in Figure 7 and Figure 8.
Year | No. samples catch | No. otoliths (catch) | No. samples (survey) | No. aged (survey) |
---|---|---|---|---|
2008 | 32 | 1600 | 282 | 475 |
2009 | 27 | 1350 | 277 | 434 |
2010 | 29 | 1449 | 241 | 363 |
2011 | 28 | 1400 | 270 | 728 |
2012 | 35 | 1750 | 285 | 750 |
2013 | 23 | 1150 | 275 | 536 |
2014 | 28 | 620 | 241 | 559 |
2015 | 26 | 555 | 260 | 573 |
2016 | 14 | 290 | 259 | 676 |
2017 | 8 | 160 | 245 | 571 |
2018 | 9 | 180 | 247 | 549 |
2019 | 15 | 330 | 251 | 704 |
2020 | 14 | 290 | 250 | 647 |
2021 | 15 | 291 | 278 | 811 |
2022 | 14 | 287 | 313 | 897 |
2023 | 18 | 355 | 302 | 954 |
Weight at age
Weight-at-age from catch from 5.a is shown in Figure 9. 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 (Figure 10).
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 2022c). 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 2011 the ‘Faroe Ridge’ survey area was included in the estimation of survey indices. 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.
Stock weight-at-age
Mean weight at age in the survey is shown in Figure 15. Stock weights are obtained from the groundfish survey in March and are also used as mean weight at age in the spawning stock. Mean weight of the oldest year classes has been gradually increasing since the early 2000s, whereas the mean weight at age of younger tusk is more variable between years.
Stock maturity at age
Maturity at age data is taken from the autumn groundfish survey and calculated based on maturity at length each year and length distributions of fish assigned to each age. The spring survey data is not used because maturation patterns appeared to occur at larger fish and differed between sexes. 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)
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.
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
There have been no marked changes in the number of boats or the composition of the fleet participating in the tusk fishery in 5.a (Table 1). Catches decreased from around 9000 tons in 2010 to 3046 tonnes in 2023. This decrease is mainly because of reductions in landings by the Icelandic longline 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, except in the last two years when the stock has experienced an all-time low. As this all-time low is more likely due to the low recruitment during 2010–2011 rather than overexploitation, so is expected to increase as subsequent higher recruitment levels grow to fishable sizes. There are no marked changes in the length compositions since 2004, mean length in the catch ranges between 52 and 58 (Figure 6). Length distributions from the spring survey show a distinct large cohort, or series of consecutive cohorts, appearing in 2014, growing through time, and just beginning to reach fished sizes approximately this year. 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.
At WGDEEP 2011 the Iceland-Faroe Ridge was included in the survey index when presenting the results from the Icelandic spring survey for tusk in 5.a. The total biomass index and the biomass index for tusk larger than 40 cm (reference biomass) decreased substantially but increased again and has remained at relatively high similar level as in 2011 (Figure 7). The same holds for the index of tusk larger than 60 cm (spawning–stock biomass index). 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 year on year in the 2014–2017 surveys. 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 the spring survey except for the juvenile abundance index that is more or less at a constant level compared to the spring survey juvenile index. Due to a labour strike, the autumn survey did not take place in 2011.
When looking at the spatial distribution from the spring survey, around 25% of the index is from the SE area. However only around 4% of the catches are caught in this area (Figure 3 and Figure 4). The change in juvenile abundance between 2006 and recent years can be seen in Figure 7.
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, s 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 2022c). 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 (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 2022c).
Data used by the assessment and model settings
Data used for tuning and the model configuration are given in the stock annex (ICES 2022b).
Model fit
Model results are shown in Table 7. The model fit to survey indices are shown in Figure 12 and Figure 13. Generally, the model closely follows the spring survey data, which are in good agreeance. The autumn survey is noisier but generally follows the same pattern. Fits to the April gillnet survey (age 10 abundance) are much noisier. An overview of model parameter estimates are shown in ?@fig-fig19.
Model results
The spawning stock biomass has shown a gradual decline prior to 1995, although prior to 1985 the model is informed by very little data, so uncertainty is high. The period 1995-2015 was steady, with a gradual decline thereafter that continued until 2021, when biomass levels have started to increase 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 as the newest higher recruitment levels grow into the fishable population. The previous peak in recruitment (2004-2005) likely did not increase spawning stock biomass levels substantially during this period due to higher fishing rates and catch values during 2008-2010, when these fish would have been entering the fishery (Figure 20).
Retrospective analysis
The results of an analytical retrospective analysis are presented (Figure 21). The analysis indicates generally consistent model results over the 5-year peel. Mohn’s ρ was estimated to be 0.0219224 for SSB, 0.0316901 for F, and 0.0865775 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 18), 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 7). Therefore, it is likely that the increase in biomass observed this year will continue in the next year or so.
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 22 and Figure 23). However, a better model configuration could not be found in the 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 25).
Management
The Icelandic Ministry of Food, Agriculture and Fisheries 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 6).
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 related to fishing activity of foreign vessels in restricted areas within the Icelandic EEZ. Faroese vessels are allowed to fish 5600 t of demersal fish species in Icelandic waters which includes a maximum 1200 tonnes of cod and 40 t of Atlantic halibut. The rest of the Faroese demersal fishery in Icelandic waters is mainly directed at tusk, ling, and blue ling. The tusk advice given by MFRI and ICES for each quota year is, however, for all catches, including foreign catches.
Figure 25 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 25).
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 | 1314 | 5569 |
2013/2014 | 6300 | 6300 | 4850 | 487 | 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 | 2420 | 640 | 3060 |
2023/2024 | 5139 | 5139 | |||
2024/2025 | 5914 |
Management considerations
Increased catches in 14.b, and now 14.a also, from less than 100 tons in previous years to around 900 tons in 2015 are of concern. Catches reduced after but have been around 150-800 tons since. In 2023, catches were also substantial, close to 800 tonnes. 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 shown high levels after a low in 2011. A reduction in fishing mortality 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 the Icelandic spring survey 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.
YEAR | BIOMASS | SSB | REC1 | CATCH | F |
---|---|---|---|---|---|
1979 | 39055 | 16360 | 11896 | 6711 | 0.089 |
1980 | 39785 | 17573 | 10942 | 6706 | 0.103 |
1981 | 39931 | 19179 | 9327 | 6663 | 0.107 |
1982 | 38946 | 19099 | 7741 | 6370 | 0.113 |
1983 | 38793 | 18908 | 6464 | 6918 | 0.154 |
1984 | 31853 | 13821 | 6952 | 6032 | 0.138 |
1985 | 28982 | 11473 | 8708 | 5129 | 0.136 |
1986 | 29518 | 12040 | 8990 | 5541 | 0.138 |
1987 | 29824 | 12565 | 9085 | 5709 | 0.150 |
1988 | 29818 | 12388 | 7538 | 6722 | 0.170 |
1989 | 30118 | 12230 | 5728 | 7267 | 0.185 |
1990 | 27260 | 10606 | 5125 | 7323 | 0.211 |
1991 | 24750 | 8850 | 4690 | 8960 | 0.228 |
1992 | 23664 | 8007 | 4640 | 8414 | 0.247 |
1993 | 19324 | 6268 | 6165 | 5950 | 0.246 |
1994 | 17584 | 5478 | 7838 | 5979 | 0.278 |
1995 | 19457 | 5504 | 11580 | 6054 | 0.372 |
1996 | 18452 | 5446 | 14651 | 5815 | 0.391 |
1997 | 19078 | 5805 | 15101 | 5306 | 0.349 |
1998 | 19432 | 6312 | 14042 | 5069 | 0.341 |
1999 | 20808 | 7254 | 14101 | 6093 | 0.383 |
2000 | 19801 | 6993 | 19019 | 5304 | 0.332 |
2001 | 19850 | 5917 | 20646 | 4817 | 0.350 |
2002 | 20867 | 5847 | 22284 | 5192 | 0.373 |
2003 | 22341 | 5983 | 24861 | 5423 | 0.336 |
2004 | 24230 | 6344 | 25054 | 4999 | 0.287 |
2005 | 27463 | 6574 | 24838 | 5510 | 0.279 |
2006 | 30786 | 7595 | 22679 | 6715 | 0.316 |
2007 | 32707 | 7556 | 18519 | 8130 | 0.360 |
2008 | 36110 | 7134 | 11594 | 8932 | 0.426 |
2009 | 34826 | 6679 | 7735 | 8998 | 0.451 |
2010 | 30833 | 6186 | 6205 | 8686 | 0.462 |
2011 | 29829 | 6122 | 4476 | 8202 | 0.399 |
2012 | 29961 | 6735 | 4218 | 7909 | 0.425 |
2013 | 27831 | 5342 | 6642 | 6421 | 0.411 |
2014 | 27374 | 4857 | 13326 | 6409 | 0.334 |
2015 | 22954 | 4874 | 17458 | 5945 | 0.325 |
2016 | 23470 | 4757 | 16906 | 4175 | 0.239 |
2017 | 22966 | 5011 | 21931 | 3333 | 0.208 |
2018 | 21181 | 4572 | 16110 | 3581 | 0.242 |
2019 | 20886 | 4039 | 17551 | 3784 | 0.247 |
2020 | 20486 | 3934 | 19733 | 2769 | 0.274 |
2021 | 22751 | 3918 | 24355 | 3144 | 0.219 |
2022 | 29213 | 5308 | 28568 | 3310 | 0.158 |
2023 | 35801 | 7086 | 38064 | 3606 | 0.145 |
2024 | 40987 | 8749 | 43736 | 3502 | 0.146 |
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. “Stock Annex: Tusk (Molva molva) in Division 5.a (Icelandic grounds).” International Council for the Exploration of the Seas; ICES publishing. Unpublished
2022d. 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