Megrim

Lepidorhombus whiffiagonis


Technical report
Published by

Marine and Freshwater Research Institute, Iceland

Published

6 June 2025

Key signals

  • Biomass indices from stock surveys reached a minimum in 2022 but are showing slight signs of recovery.

  • Recruitment failure occurred during the years 2012–2020. A large recruitment peak is visible in SMB spring 2025.

  • In the surveys, the peak of the length distribution has gradually shifted to the right, toward larger fish, reflecting a period of poor recruitment. However, the average length decreased significantly in the SMB this year.

  • Total biomass peaked in 2006 in the spring survey.

  • Fishing mortality (F) has always been below FMSY.

  • The megrim stock in Iceland is still at a low point, but due to the emergence of a strong recruitment pulse, it is important to monitor the development of the stock.

General information

Megrim is a demersal species on a sandy or muddy substrate, occurring at depths ranging from 40-400 m, but is most common at 100-200 m. Its distribution is confined to the relatively warm waters south and west of Iceland. In Icelandic waters the females can reach 70 cm in length, but males about 60 cm. Size at sexual maturity differs between the sexes. At the length of 32 cm about half the males have reached maturity, but half the females have reached maturity at 42 cm.

Fishery

The geographical distribution of the megrim fisheries in ICES area 5a (Iceland grounds) has remained more or less unchanged in recent years (Figure 1), with the main fishing grounds in the south (southwest and southeast) of Iceland, extending along the south coast in the deeper areas. There is no target fishery for megrim in Iceland and it is taken as bycatch in other fisheries. Spatial distribution of the Icelandic megrim fishery is relatively stable, with around 90% caught off the south coast (Figure 2). In recent years, reported catches have increased as megrim was inadequately reported in logbooks before 2009

Megrim is caught at a relatively great depth compared to most other flatfish species, and a large portion of the catch (50–80%) has been taken at depths of 100–250 meters (Figure 3). However, in 2022, about half of the catch was taken at depths over 250 meters, alongside a decline in landed catch (Figure 4). Over the past two years, that proportion has decreased.

Megrim is caught as bycatch in Icelandic fisheries, in demersal seine, Nephrops- and demersal trawl fisheries (Figure 4 and Table 1). The megrim catch taken by seiners has decreased significantly in recent years and accounted for around 10% over the past three years. The catch in Nephrops and demersal trawls increased between 2009 and 2020. The catch in Nephrops trawls declined in 2021 due to reduced Nephrops fishing and area restrictions and ceased entirely due to a fishing ban in 2022. In 2024, about 90% of landed megrim was caught by demersal trawl (Figure 4).

In recent years, the number of vessels landing megrim annually has declined significantly (Table 1).

The number of vessels responsible for catching 95% of the megrim catch in Icelandic waters has decreased from 63 vessels in 1996 to just under 20 vessels over the past seven years (Figure 5). The sharp decline in vessels between 1997 and 2005 aligns with reduced megrim catches. Since 2005, the number of vessels has continued to decrease, while the catch has been more variable. Since 2016, only 20 vessels have landed 95% of the megrim catch.

Figure 1: Megrim in 5a. Spatial distribution of catches by all gears according to Icelandic logbooks.
Figure 2: Megrim in 5a. Changes in spatial distribution of megrim catches as recorded in Icelandic logbooks.
Figure 3: Megrim in 5a. Depth distribution of megrim from Nephrops and demersal trawl and seine according to Icelandic logbooks.
Figure 4: Megrim in 5a. Landings in tonnes and percent of total by gear and year.
Table 1: Megrim in 5a. Number of Icelandic vessels landing megrim, and all landed catch (in tonnes) divided by gear type.
Year Nr. Demersal Seine Nr. Bottom Trawl Nr. Nephrops Trawl Nr. Other Demersal Seine Bottom Trawl Nephrops Trawl Other Total Catch
2000 30 60 23 23 52 34 13 1 100
2001 28 44 21 25 55 27 16 1 98
2002 17 33 27 19 35 22 25 0 82
2003 30 32 21 14 50 11 12 0 73
2004 30 30 20 9 87 15 21 0 123
2005 26 25 14 11 106 18 24 0 148
2006 24 34 19 8 216 28 41 0 285
2007 27 26 12 15 120 43 25 0 187
2008 26 31 17 10 126 34 36 0 197
2009 28 30 14 14 195 51 74 1 322
2010 24 30 15 6 89 52 111 0 252
2011 22 30 15 9 89 63 169 0 321
2012 24 26 16 4 121 71 218 0 411
2013 18 24 15 9 98 50 228 0 376
2014 15 24 16 3 73 86 179 0 339
2015 16 28 13 7 48 149 281 0 478
2016 14 29 12 6 56 207 199 0 461
2017 9 24 9 2 32 173 234 0 440
2018 11 24 9 3 36 147 185 0 368
2019 14 30 8 2 26 106 199 0 331
2020 13 29 8 4 19 108 141 0 268
2021 12 28 7 4 5 119 51 0 175
2022 11 33 2 4 13 73 1 0 88
2023 15 36 0 0 10 71 0 0 81
2024 14 33 1 2 6 39 1 0 46
Figure 5: Megrim in 5a. Number of vessels (all gear types) accounting for 95% of the total catch annually since 1994. Left: Plotted against year from 1994. Right: Plotted against total catch. Data from the Directorate of Fisheries.

Catch per unit effort (CPUE) and effort

CPUE estimates of Megrim 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.

CPUE of demersal trawl and Nephrops trawl (kg/hour), in hauls where megrim is caught, gradually increased in 2010-2021, however decrease was in demersal trawl CPUE over the past three years (Figure 6).

CPUE in demersal seine (kg/set) is calculated as the total weight in sets in which megrim was caught. CPUE gradually decreased from 125 kg/set in 2013-2016 to about 50 kg/set in 2024 (Figure 6).

Figure 6: Megrim in 5a. Catch per unit of effort in the most important gear types. The dashed lines are based on locations where more than 10% of the catch is megrim and solid lines on all records where megrim is caught.

Sampling overview

Sampling and measurements of megrim from the catch of the main fishing gears began in 1996. Table 2 shows the number of samples along with length-measured and otolith-sampled fish since 1996. Typically, 90–97% of otoliths from the catch are aged, although this has not been done since 2019. No catch samples were taken in 2024.

Table 2: Megrim in 5a. Number of samples, length measurements and otoliths sampled from landed catch.
Year
Bottom Trawl
Demersal Seine
Nephrops Trawl
Num. samples Num. lengths Num. otiliths Num. samples Num. lengths Num. otiliths Num. samples Num. lengths Num. otiliths
1996 0 0 0 0 0 0 1 399 100
1998 0 0 0 0 0 0 1 102 100
1999 1 35 25 4 166 89 3 203 103
2000 0 0 0 6 451 150 1 75 25
2001 1 75 25 4 300 100 2 150 50
2002 0 0 0 4 300 100 3 301 50
2003 0 0 0 4 299 100 0 0 0
2004 0 0 0 7 533 175 1 75 25
2005 1 73 0 12 864 300 2 151 50
2006 0 0 0 28 2 209 550 1 75 25
2007 1 75 25 10 745 250 0 0 0
2008 0 0 0 15 1 129 344 2 161 25
2009 1 74 25 22 1 597 477 6 450 150
2010 0 0 0 9 667 225 8 600 200
2011 1 49 0 8 565 200 16 1 215 401
2012 2 150 50 13 944 299 19 1 417 475
2013 4 300 100 11 825 275 12 870 300
2014 0 0 0 4 301 100 4 295 95
2015 2 178 25 5 374 124 9 668 225
2016 1 75 25 3 213 75 5 375 125
2017 0 0 0 2 150 50 7 527 175
2018 1 75 25 2 151 50 3 193 75
2019 0 0 0 2 150 50 7 792 125
2020 1 125 25 0 0 0 2 144 25
2021 1 125 25 0 0 0 1 61 25
2022 3 311 60 2 104 40 0 0 0
2023 3 475 20 0 0 0 0 0 0

Length distribution of landed catch

The relative length distribution of landed megrim catch was fairly stable during the years 2001–2009, with an average length between 47–49 cm (Figure 7). Since 2010, landings of larger megrim have increased, and the average length reached 57 cm in 2023.

Figure 7: Megrim in 5a. Commercial length distributions by gear and year

Icelandic survey data

The Icelandic spring groundfish survey (hereafter spring survey, IS-SMB), which has been conducted annually in March since 1985, covers the most important distribution area of the megrim fishery. In addition, survey data on megrim is available from the Icelandic autumn groundfish survey (hereafter autumn survey, IS-SMH) since 1996. The autumn survey was not conducted in 2011. The spring survey is considered to measure changes in abundance/biomass better than the autumn survey.

Figure 8 shows trends in various biomass indices and a recruitment index based on abundance of megrim smaller than 20 cm. Abundance and changes in spatial distribution are shown in Figure 9, Figure 10 and survey length-disaggregated abundance indices in Figure 11.

Total biomass index and the biomass index for megrim larger than 40 cm (harvestable part of the stock) increased steadily between 2000 and 2007 and stayed relatively stable until 2018. Then the SMB indices decreased and reached their lowest level in 2022, but increased slightly since (Figure 8). The index of megrim larger than 53 cm gradually increased in years 2000-2018, then decreased abruptly in 2022 but increased again to a quite high level. The index of juvenile abundance (<20 cm) was historically low in years 2012-2020 until SMB 2025 when a very large recruitment pulse was observed (Figure 8).

In the SMB 2025, megrim was caught entirely off the south (southwest and southeast) and west coasts, primarily at around 300 meters depth. The distribution of megrim has changed little since the start of the SMB series, with most catches occurring off the southern and western coasts (Figure 9; Figure 10). The distribution of megrim in the SMH survey for year 2024 is similar to that observed in the SMB survey for year 2025. The same pattern has held since the beginning of the SMH series, with the highest catches off the southwest and west coasts.

The relative length distribution of megrim from the SMB survey (Figure 11) has fluctuated somewhat over the time period. Recruitment pulses were observed in 2000–2001 and 2024–2025, during which the average length dropped to 29–33 cm. Between 2012 and 2023, the length distribution shifted markedly to the right, with no visible recruitment pulses until spring 2024. This year, a strong recruitment pulse was seen, matching the small one observed the previous year. In the SMH survey, the length distribution has also shifted to the right, but patterns are difficult to interpret due to the low number of individuals caught in recent years (Figure 11).

Figure 8: Megrim in 5a. Indices in the spring survey (SMB) 1985 and onwards (line shaded area) and the autumn survey (SMH) (point ranges).
Figure 9: Megrim in 5a. Location of Megrim in the most recent spring (SMB) and autumn (SMH) surveys, bubble sizes are relative to catch sizes.
Figure 10: Megrim in 5a. Changes in geographical distribution of the survey biomass.