Atlantic wolffish

Fishery

The main fishing grounds for Atlantic wolffish are in the west and northwest part of the Icelandic shelf. From 2010, the proportion of the catch has been increasing in northwest of Iceland compared to west of Iceland. Catches at the main spawning ground (Látragrunn) west of Iceland have been decreasing since 2008 (Figure 1 and Figure 2). About 80% of the catch of Atlantic wolffish is caught at depths less than 120 m. Proportion of the catch taken at depth range 0-60 m decreased from 2003 to 2007, but since then it has been increasing. At the depth range 61-120 m the proportion of the catch has been rather stable since 2000. At depths from 121 to 180 m, which includes the main spawning ground (Látragrunn), it the proportion of the catch increased in 2003-2008 but since then it has been decreasing (Figure 3).

Figure 2: Atlantic wolffish. Spatial distribution of the Icelandic fishery by fishing area since 2000 according to logbooks. All gears combined.

Figure 3: Atlantic wolffish. Depth distribution of demersal trawl, longline and demersal seine catches according to logbooks.

Landings trend

More than 97% of the Atlantic wolffish catch is taken by longliners (50-65%), demersal trawlers (20-30%) and demersal seiners (about 10%) (Figure 4). These proportions have been relatively stable through the years. However, in 2004-2008 longline and demersal trawl catches were similar (40-50%) and in the last three years catches by demersal seiners hasve been increasing and are now greater than in demersal trawlers (Figure 4). Since 2001, the number of longliners and trawlers reporting Atlantic wolffish catches of 10 tonnes/year or more has decreased. In the longline fleet, the number of vessels has dropped from 198 in 2001, down to 36 in 2023. The number of trawlers has also decreased significantly from 76 in 2000 to 49 in the last year (Table 1).

Figure 4: Atlantic wolffish. Total catch (landings) by fishing gear since 1994, according to statistics from the Directorate of Fisheries.

In 1994 and 1995, more than 500 vessels accounted for 95% of the annual catch of Atlantic wolffish in Icelandic waters, but this number had dropped to 200 vessels in 2008 despite higher catches. Since 2010 the number of vessels accounting for 95% of the annual catch has remained relatively constant (about 150-200 vessels), despite catch reductions (Figure 5).

Table 1: Atlantic wolffish. Number of Icelandic boats and catches by fleet segment participating in the Atlantic wolffish fishery from logbooks.
Year	nr. longlines	nr. bottom trawls	nr. seiners	nr. other gear	Catch longlines	Catch bottom trawls	Catch seiners	Catch other gear	Total
2000	161	53	16	0	8687	3380	528	0	12595
2001	195	59	14	1	11267	3391	513	11	15182
2002	140	44	13	0	7773	3735	601	0	12110
2003	138	45	19	0	7785	5463	1066	0	14313
2004	103	34	29	0	4670	4773	1609	0	11052
2005	91	47	24	1	5445	6893	1140	30	13508
2006	120	48	25	0	6626	6286	1149	0	14061
2007	105	60	24	0	5259	7566	1338	0	14163
2008	87	60	22	3	4663	6960	1427	44	13093
2009	114	55	28	1	6708	5468	1205	10	13391
2010	74	46	20	3	5916	4436	842	92	11286
2011	64	37	18	0	5344	3565	1010	0	9918
2012	66	24	22	1	5328	2827	895	41	9091
2013	73	30	18	2	4652	2341	647	22	7662
2014	70	23	13	1	3681	1637	891	11	6220
2015	56	34	17	2	3989	1905	926	28	6848
2016	61	37	18	2	4848	1662	1127	25	7661
2017	59	28	18	2	3829	1102	1095	23	6049
2018	60	37	27	6	4923	1587	2186	74	8770
2019	64	34	21	1	4595	1630	2168	11	8404
2020	46	38	24	1	2491	2046	2040	11	6588
2021	45	48	22	0	3343	3021	2086	0	8451
2022	40	48	23	0	2706	2986	2275	0	7967
2023	36	49	20	0	3154	2756	2388	0	8298

Figure 5: Atlantic wolffish. 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.

Data available

The commercial catch samples taken are normally representative of the landings with most number of samples taken in areas of high catch intensity (Figure 7).

Figure 6: Atlantic wolffish. Spatial distribution of length samples (black dots) from commercial catches in Icelandic waters (upper) and numbers of samples taken per month by project (bars) and proportion of landings per month (black line) (lower).

Landings and discards

Landings by Icelandic vessels are given by the Icelandic Directorate of Fisheries. Landings of Norwegian and Faroese vessels are given by the Icelandic Coast Guard. Discarding is banned by law in the Icelandic demersal fishery, as well as in Norway. Measures in the Icelandic management system such as converting quota share from one species to another are used by the Icelandic fleet to a large extent, and this is thought to discourage discards in mixed fisheries.

Sampling from commercial catches

In 1969-1997, on average 500 otoliths were sampled annually, except in 1970, 1973, and 1974 when no otoliths were sampled. In 1999, the effort of sampling Atlantic wolffish from commercial catch was increased. In the years 1999-2014 annual sampling of aged fish was 1600-3000 or on average 2200, but since 2015 this average has been around 1200 fish. In 2023, a total of 12, 21 and 25 samples were collected from longline, demersal trawl and demersal seine catches, respectively (Table 2, Figure 6).

Table 2: . Atlantic wolffish. Number of samples and aged fish from landed catch of Atlantic wolffish.
Year	Longline (nr. of samples)	Longline (nr. fish)	Bottom trawl (nr. of samples)	Bottom trawl (nr. fish)	Demersal seine (nr. of samples)	Demersal seine (nr. fish)
2000	29	1395	18	752	4	200
2001	27	1343	11	509	3	150
2002	25	1240	16	645	2	100
2003	31	1525	20	899	6	300
2004	19	950	23	1060	8	400
2005	15	746	25	1202	6	292
2006	23	1110	21	1029	5	250
2007	18	900	25	1250	10	451
2008	19	950	25	1248	4	200
2009	16	800	20	999	4	200
2010	29	1669	19	1090	5	285
2011	14	750	15	778	9	550
2012	26	1300	14	700	7	350
2013	25	1249	14	691	4	200
2014	30	800	26	675	28	700
2015	25	625	19	479	19	474
2016	25	625	13	325	9	225
2017	23	575	9	220	6	150
2018	22	550	9	225	17	425
2019	22	550	11	276	20	500
2020	9	225	14	350	16	400
2021	14	350	25	625	15	375
2022	3	60	23	465	17	338
2023	12	240	21	420	25	499

Length composition

The length distribution of landed Atlantic wolffish has been relatively stable since 2005 (Figure 7).

Figure 7: Atlantic wolffish. Length distribution from the Icelandic fleet from 2005-2023.

Age composition

Age composition data are available from surveys and from commercial catch. Commercial age data are available from earlier periods (1978). In samples from commercial landings, the mean age of Atlantic wolffish was around 10.7 years in 1999. Since then, mean age in samples from commercial catches has generally been increasing to around 12 years in recent years. In 2023, 8-16 year old fish are most common in catch (Figure 8 and Figure 9)

Figure 8: Atlantic wolffish. 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 9: Atlantic wolffish. Catch at age from the commercial fishery in Iceland waters. Biomass caught by year and age; bars are coloured by cohort.

Weight-at-age

Weight-at-age data in Icelandic waters are available from 1996. Weight of the oldest year classes has been above average for the past years (Figure 10). Catch weight are shown in Figure 11.

Figure 11: Atlantic wolffish. Catch weights by age from the commercial fishery in Icelandic waters.

Catch and effort

CPUE estimates of Atlantic wolffish in Icelandic waters are not considered representative of stock abundance, as changes in fleet composition, technical improvements and differences in gear setup among other things have not been accounted for when estimating CPUE. Non-standardized estimates of CPUE in longline (kg/1000 hooks), and demersal trawl (kg/hour), are calculated as the total weight in sets or tows in which Atlantic wolffish was more than 10% of the catch, according to logbooks. Effort of demersal trawl was defined as the number hours towed, and for longline number of hooks, in both cases where Atlantic wolffish was more than 10% of the catch. CPUE in longline vessels has been similar among years prior to 2018, around 100-150 kg/1000 hooks. CPUE of demersal trawl increased from about 230 to 400 kg/h in 2000-2005, but since 2006 it has fluctuated at around 250-300 kg/h (Figure 12). Both indices have shown a sharp decrease over the past three years. Fishing effort in longline increased from 66 million hooks in 2000 to 97 million hooks in 2001. Since then it has been generally decreasing and was around 22 million hooks in 2018. In demersal trawl, fishing effort increased from about 14 thousand tow-hours in 2004 to 23 thousand tow-hours in 2008, followed by a sharp decrease to 4.8 thousand tow-hours in 2014. Since then it has increased.

Figure 12: Atlantic wolffish. Non-standardized estimates of CPUE for demersal trawl (left, kg/h) and longline (right, kg/1000 hooks).

Survey data

The Icelandic spring groundfish survey (hereafter spring survey, IGFS), which has been conducted annually in March since 1985, covers the most important distribution area of Atlantic wolffish in Icelandic waters. In addition, the Icelandic autumn groundfish survey (hereafter autumn survey, IAGS) was started in 1996 and expanded in 2000. However, a full autumn survey was not conducted in 2011 due to a labour strike. Because the spring survey covers the main distribution area, it is considered adequate to measure changes in abundance/biomass of Atlantic wolffish better than the autumn survey. Total biomass and harvestable biomass indices decreased from 1985-1995. In 1996, the biomass index increased to 1998, then decreased to a historical low level in 2010-2012, but since then it has been increasing Figure 14). The harvestable biomass has generally been increasing from 1995 with considerable oscillators. The recruitment index was high in the years 1992-2003, since 1999 it has been decreasing, which coincides with increasing effort and catch of trawlers at the main spawning ground west of Iceland (Látragrunn) during the spawning and incubation time. The recruitment index reached a historical low level in 2011, but since then it has been rather stable or increased slightly. This coincides with that the closed spawning/incubation area on Látragrunn was enlarged from 500 km2 (from 2002) to 1000 km2 in October 2010.

When the spring survey is conducted, Atlantic wolffish are on their feeding grounds which are commonly in relatively shallow waters. In the spring survey, the highest abundance has always been measured in the NW area (Figure 15).

Figure 13: Atlantic wolffish. Location and abundance of ling in the spring survey (SMB) in 2024 and the autumn survey (SMH) in 2023.

Figure 14: Atlantic wolffish. Total biomass indices (upper left) and harvestable biomass indices (≥60 cm, upper right), large fish biomass indices (≥80 cm, lower left) and juvenile abundance indices (≤40 cm, lower right), from the spring survey (blue) and the autumn survey (red), along with the standard deviation.