ATLANTIC HALIBUT

Hippoglossus hippoglossus


Technical report
Published by

Marine and Freshwater Research Institute, Iceland

Published

7 June 2024

General information

Atlantic halibut is the largest flatfish species in the world’s oceans and the largest bony fish in Icelandic waters. The largest recorded measurement in Iceland is from the year 1935, when a 365 cm long halibut was caught off the north coast, weighing 266 kg. It matures slowly; at the length of 80 cm about half of the males have reached maturity, whereas females reach that level at 103 cm.

Atlantic halibut is found all around Iceland but is most common off the west and south coasts. It is a demersal species on muddy, sandy or gravel substrate, and sometimes even on hard bottoms at 20-2000 m depths. The juvenile halibut occupy relatively shallow waters, up to the age of 3-5 years, after which they migrate to deeper waters of the continental shelf and slope.

Atlantic halibut is known for occasional long-distance migrations. Individuals tagged in Icelandic waters have been recaptured off Faroe Islands, East- and West-Greenland, and in the waters off Newfoundland. Recaptures from Iceland include fish tagged in Faroe Islands and Canada.

Fishery

The geographical distribution of the Atlantic halibut fishery has changed since 2011 following a ban on targeted fishing as well as mandatory release of all viable fish (Figure 1).

In 2000-2011, the main fishing grounds for Atlantic halibut were in the western part of the Icelandic shelf (Figure 2 and Figure 1) according to logbook entries. After the ban on targeted fishing, most of the landed catch has been taken on demersal trawl fishing grounds in the west and northwest areas (Figure 2).

Targeted fishing was mainly conducted in deep waters, over 300 m depth (Figure 3). The ban on targeted fishing particularly affected the amount of Atlantic halibut taken in these deeper waters.

Atlantic halibut on Icelandic fishing grounds was mainly caught on longline and in demersal trawl, or approximately 85% of landings in 2006-2011 (Table 1). After the ban in 2011, most of the landed catch comes from demersal trawlers (Table 1 and Figure 4). Close to no catch is landed from longliners after the ban and this fleet segment reports most of the releases of live halibut (Table 2). The reported number of released halibut increased since 2018 and so has the number of vessels that have reported released fish (Table 2). In 2021 the number of longliners reporting releases of live halibut increased significantly and the number of viable halibut released. Data on released halibut in 2023 were not accessible when this report was published. No biological samples were taken from landed catch since 2020.

Table 1: Atlantic halibut in 5a. Number of Icelandic vessels landing Atlantic halibut, and all landed catch divided by gear type.
Year Nr. Long Line Nr. Bottom Trawl Nr. Danish Seine Nr. Other Long Line Bottom Trawl Danish Seine Other Total catch
2000 349 137 79 275 171 203 85 36 495
2001 348 136 85 343 255 216 95 61 627
2002 309 129 82 317 272 246 116 46 680
2003 320 126 88 303 202 220 141 68 631
2004 331 118 84 284 218 217 94 40 569
2005 327 119 79 204 205 225 54 37 521
2006 319 107 73 157 228 178 38 20 464
2007 295 107 70 113 187 182 39 21 429
2008 252 97 63 96 242 191 46 19 498
2009 235 92 61 120 298 165 47 19 529
2010 207 84 50 149 386 127 34 13 560
2011 195 79 47 172 423 89 24 12 548
2012 33 54 0 23 1 33 0 1 35
2013 46 67 21 25 2 35 1 3 41
2014 61 60 17 30 6 33 4 2 45
2015 0 63 18 17 0 72 9 2 83
2016 0 70 17 23 0 113 4 2 119
2017 0 67 25 19 0 85 16 1 102
2018 0 64 29 28 0 115 16 3 134
2019 0 59 30 23 0 103 22 2 127
2020 11 64 29 22 1 120 17 3 141
2021 0 63 30 31 0 134 16 3 153
2022 14 62 27 29 23 152 17 3 195
2023 12 55 25 36 19 137 17 4 177

Figure 1: Atlantic halibut in 5a. Spatial distribution of catches by all gears according to Icelandic logbooks.

Figure 2: Atlantic halibut in 5a. Changes in spatial distribution of Atlantic halibut catches as recorded in Icelandic logbooks.

Figure 3: Atlantic halibut in 5a. Depth distribution of Atlantic halibut from longline, demersal trawl and seine according to Icelandic logbooks.

Figure 4: Atlantic halibut in 5a. Landings in tonnes and percent of total by gear and year.

Table 2: Atlantic halibut. Number of released Atlantic halibut by year and fishing gear, and number of Icelandic vessels that reported released halibut.
Year Nr. lonline Longline nr. fish Nr. bottom trawl Bottom trawl nr. fish Nr. demersal seine Demersal seine nr. fish Nr. gilnetters Gilnets nr. fish
2017 7 472 1 1 0 0 0 0
2018 13 2044 0 0 0 0 3 7
2019 12 2214 1 3 1 95 0 0
2020 5 2480 1 2 1 33 1 1
2021 14 7723 1 10 2 66 0 0
2022 8 2536 1 1 1 5 2 8

Sampling overview

Table 3: Atlantic halibut. Number of samples and length measurements from landed catch.
Year Bottom Trawl - nr. samples Bottom Trawl - nr. lengths Demersal Seine - nr. samples Demersal Seine - nr. lengths Longline - nr. samples Longline - nr. lengths
1981 1 157 0 0 0 0
1982 5 1336 0 0 1 108
1984 0 0 2 199 0 0
1985 0 0 1 189 0 0
1986 0 0 0 0 1 135
1989 0 0 0 0 1 19
1991 0 0 1 11 0 0
1994 0 0 1 122 0 0
1995 0 0 0 0 2 63
1996 1 27 2 249 0 0
1997 1 2 1 57 1 1
1998 51 215 2 199 8 104
1999 63 309 1 83 1 26
2000 24 86 2 168 2 31
2001 2 30 1 76 0 0
2002 1 17 0 0 0 0
2003 1 5 1 4 0 0
2004 0 0 1 27 0 0
2007 3 63 0 0 1 1
2008 0 0 0 0 1 65
2009 0 0 0 0 2 16
2011 1 3 0 0 0 0
2012 5 9 0 0 0 0
2013 3 21 0 0 0 0
2017 0 0 0 0 2 5
2019 11 60 2 3 0 0
2020 6 26 0 0 0 0

Icelandic survey data

The Icelandic spring groundfish survey (hereafter spring survey or SMB), which has been conducted annually in March since 1985, covers the most important area of the Atlantic halibut fishery on the continental shelf. It does, however, not cover the habitats of mature fish in deeper waters further offshore. In addition, the Icelandic autumn groundfish survey (hereafter autumn survey or SMH) was commenced in 1996. The autumn survey was not conducted in 2011. The spring survey is considered to measure changes in abundance/biomass of immature halibut better than the autumn survey, but both surveys are inadequate at estimating spawning stock biomass.

Figure 5 shows trends in various biomass indices and a recruitment index based on abundance of Atlantic halibut 30 cm and smaller. Survey length disaggregated abundance indices are shown in Figure 8, and abundance and changes in spatial distribution in Figure 7.

Biomass indices are at similar levels as in the 1990s and early 2000s, except for recruitment index which has remained at lowest levels since 2000.

Figure 5: Atlantic halibut in 5a. Indices in the spring survey (March) 1985 and onwards (line shaded area) and the autumn survey (October) (point ranges).

Figure 6 shows the relative index, indicating no clear difference between the surveys in terms of the total biomass and total abundance of the Atlantic halibut.

Figure 6: Atlantic halibut in 5a. Relative index, SMB in blue and SMH in black.

Atlantic halibut is mainly caught in the NW and W areas in the spring survey (Figure 7 and Figure 8), although a considerable proportion of the biomass index in 2002-2010 comes from the SE area (Figure 7). Catches of Atlantic halibut in the autumn survey are rather sporadic events with no clear pattern in distribution (Figure 7 and Figure 8). However, most halibut are usually caught in the W and NW areas. Small Atlantic halibut (30-60 cm) are most common in the spring survey, while the length distribution in the autumn survey is more distributed without any noticeable peaks (Figure 9).

Figure 7: Atlantic halibut in 5a. Changes in geographical distribution of the survey biomass.

Figure 8: Atlantic halibut in 5a. Location of Atlantic halibut in the most recent spring (SMB) and the autumn (SMH) surveys, bubble sizes are relative to catch sizes.

Figure 9: Atlantic halibut in 5a. Length distributions from the spring and autumn surveys.

Management

The Ministry of Food, Agriculture and Fisheries is responsible for management of the Icelandic fisheries and implementation of legislation. In 2012, a regulation was issued to ban all targeted fishing for Atlantic halibut and stipulating that all viable halibut must be released in other fisheries (regulation no. 470/2012).

TAC is not issued for this stock.