TUSK

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).

Figure 1: Tusk. Nominal landings from Icelandic waters.

Table 1: Tusk. Number of Icelandic boats with tusk landings, landings by gear and total catches.
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.

Figure 2: Tusk. Depth distribution of catches according to logbooks. All gears combined.

Figure 3: Tusk. Catch distribution and proportions by area according to logbooks. All gears combined.

Figure 4: 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 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.

Table 2: Tusk. Nominal landings by nations in 5.a
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

Table 3: Tusk. Nominal landings by nations in 14.
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.

Figure 5: Tusk. Ratio of 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.

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.

Figure 6: Tusk. Length distributions from Icelandic commercial longline catches.

Table 4: Tusk. Number of available length measurements from Icelandic (5.a) commercial catches.
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.

Figure 7: Tusk. Catch at age from the commercial fishery in Iceland waters. Bar size is indicative of the catch in numbers and bars are coloured by cohort.

Figure 8: Tusk. Catch at age from the commercial fishery in Iceland waters. Biomass caught by year and age; bars are coloured by cohort.

Table 5: Tusk. Number of available otoliths from Icelandic (5.a) commercial catches and the Icelandic Spring survey and the number of aged otoliths.
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).

Figure 10: Tusk. Catch weights by age from the commercial fishery in Icelandic waters

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.

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 index from 1985 and the points with the vertical lines show the autumn survey from 1997. 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 survey biomass in the spring survey by year 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.

Figure 14: Tusk. Age disaggregated indices in the autumn survey and the spring survey. Fill colours indicate cohorts. Note different scales on y-axes.

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.