LONG ROUGH DAB

Hippoglossoides platessoides


Technical report
Published by

Marine and Freshwater Research Institute, Iceland

Published

7 June 2024

General information

Long rough dab is a common demersal species living all around Iceland, mainly occurring at depths ranging from 10-400 m, but has been caught down to 1200 m. Growth is relatively slow and females grow considerably larger than males. Only a small proportion of males become longer than 30 cm, while about the same proportion of females grow larger than 45 cm. At the length of 11.5 cm about half the males have reached maturity at the south coast, but females reach that level at 17.5 cm. Because of this difference in size, the fishery for long rough dab is largely based on “old” females.

Fishery

The geographical distribution of the long rough dab fisheries according to logbooks has changed significantly since 1995, where the distribution of the catch was mostly in relatively shallow areas in the southern part of the shelf (Figure 1, Figure 2). In years 1994-2004, when catches were high, about 50-70% of long rough dab was caught in the southeast (Figure 2). Since 2004 the catches have decreased significantly in all areas and annual catches have been less than 35 t since 2015 (Figure 2). Historically, most of the long rough dab was caught at less than 200 m depth, but since 2013 larger proportion of the catch has been caught in waters deeper than 200 m (Figure 3).

In Icelandic fishing grounds, long rough dab is mainly caught in demersal seine and bottom trawl, or approximately 95% of total landings (Figure 4, Table 1). Since 2000, 1-48 trawlers and 0-57 seiners have reported annual catches of long rough dab. The number of trawlers and demersal seiners have decreased in the last 20 years (Table 1).

In 1994-1997, when annual catches of long rough dab were about 5-6 thous. tonnes, around 80 vessels accounted for 95% of the catch (Figure 5). Since then, the number of vessels has dropped proportionally to reduced catches.

Table 1: Long rough dab in 5a. Number of Icelandic vessels landing long rough dab, and all landed catch divided by gear type.
Year Nr. Danish Seine Nr. Bottom Trawl Nr. Other Danish Seine Bottom Trawl Other Total catch
2000 76 81 72 2355 798 35 3188
2001 70 73 78 2771 674 35 3480
2002 64 94 60 2984 559 49 3592
2003 74 63 61 2497 319 19 2835
2004 73 52 63 1780 180 10 1970
2005 63 41 50 753 114 4 871
2006 58 36 57 639 101 5 745
2007 51 27 55 271 78 11 360
2008 44 36 79 211 51 16 278
2009 44 27 52 223 57 12 292
2010 41 27 51 173 33 13 219
2011 35 29 46 141 29 6 176
2012 31 36 49 108 27 5 140
2013 25 33 39 50 26 4 80
2014 23 28 44 26 38 7 71
2015 13 27 30 6 23 6 35
2016 9 22 13 4 12 0 16
2017 8 20 6 2 16 0 18
2018 11 24 6 1 16 0 17
2019 11 32 8 0 16 0 16
2020 6 25 9 1 22 0 23
2021 16 31 6 5 47 0 52
2022 24 31 18 23 30 1 54
2023 24 33 21 55 33 1 89

Figure 1: Long rough dab in 5a. Spatial distribution of catches by all gears according to Icelandic logbooks.

Figure 2: Long rough dab in 5a. Changes in spatial distribution of Long rough dab catches as recorded in Icelandic logbooks.

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

Figure 4: Long rough dab in 5a. Landings in tonnes and percent of total by gear and year.

Figure 5: Long rough dab in 5a. Number of vessels (all gear types) accounting for 95% of the total catch annually 1994-2021. Left: Plotted against year. Right: Plotted against total catch. Data from the Directorate of Fisheries.

Sampling overview

As landings of long rough dab have been low and sporadic over the last ten years, it has been difficult to get biological samples. Otoliths from landed catches have not been age read since 2014 and few length measurements have been taken from the catch (Table 2). During 1994-2004 period, when the main fishing for long rough dab occurred, the length distribution of landings changed little from one year to another (Figure 6). The average length was 35-36 cm over the entire period. Since then, collected samples have been fewer and average length from 32-37 cm per year.

Table 2: Long rough dab in 5a. 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 Nephrops trawl - nr. samples Nephrops trawl - nr. lengths
1993 0 0 2 752 0 0
1994 0 0 2 735 0 0
1995 0 0 3 1011 0 0
1996 0 0 10 2585 0 0
1997 1 207 16 4147 0 0
1998 2 390 11 2173 3 606
1999 4 375 21 2277 0 0
2000 6 440 17 1250 0 0
2001 2 200 20 1950 1 75
2002 0 0 21 2434 4 422
2003 6 713 22 2171 2 203
2004 1 77 24 2664 0 0
2005 4 373 22 3176 0 0
2006 0 0 20 2145 0 0
2007 1 100 10 1307 0 0
2008 0 0 10 994 0 0
2009 0 0 4 322 0 0
2010 0 0 4 437 0 0
2011 1 8 3 375 0 0
2012 0 0 4 600 0 0
2013 0 0 1 150 0 0
2014 0 0 1 72 1 171
2015 1 105 1 71 0 0
2016 0 0 1 17 0 0
2017 0 0 1 116 0 0
2019 2 167 3 109 0 0
2021 1 46 2 259 0 0
2023 0 0 1 26 0 0

Figure 6: Long rough dab in 5a. Relative length distributions from landed catch. The black line represents the mean length for all years.

Icelandic survey data

The Icelandic spring groundfish survey (hereafter spring survey), which has been conducted annually in March 1985-2020, covers the most important distribution area of the long rough dab fishery. In addition, data from the Icelandic autumn groundfish survey (hereafter autumn survey) since 1996. The autumn survey was not conducted in 2011. The spring survey is considered to measure changes in abundance/biomass of long rough dab better than the autumn survey.

Figure 7 shows various biomass indices and a recruitment index based on abundance of long rough dab. Survey length disaggregated abundance indices are shown in Figure 10, and spatial distribution in Figure 8 and Figure 9.

Total biomass and the harvestable biomass (≥30 cm) indices for long rough dab in the spring survey decreased from 2003 to the lowest level in the time series in 2018. Biomass index of larger fish (>37 cm) has decreased since 2001 and reached an all-time low in 2018. In years 2019-2021, the indices increased slightly and are considered stable. The recruitment index was high in 1991-1996 and 2011-2015, and all time highest in 2020-2021 (Figure 7).

Length distribution of long rough dab in the spring survey is characterised by three periods of increased number of small fish (<10 cm). The first period was from 1991-1996, the second from 2010-2015 and the third, with highest recruitment peak in 2020 (fig-surveyldistplot). In the years that followed the first period there was an increase in long rough dab larger than 30 cm which was not seen after the second period. Although there is more variance in the length distributions from the autumn survey, these two first periods of recruitment are also seen there (Figure 10).

Distribution of long rough dab in the spring survey shows that the species is found all around Iceland (Figure 8 and Figure 9). Most of the biomass is measured in the northern areas. This also applies to the autumn survey (Figure 8 and Figure 9). This is worth noticing, as most of the commercial catch during the main fishing years of 1994-2004 was taken in the SE area (Figure 2).

Figure 7: Long rough dab in 5a. Indices in the spring survey (March) 1985 and onwards (line shaded area) and the autumn survey (October) (point ranges).

Figure 8: Long rough dab in 5a. Changes in geographical distribution of the survey biomass.

Figure 9: Long rough dab in 5a. Location of Long rough dab in the most recent spring (SMB) and the autumn (SMH) surveys, bubble sizes are relative to catch sizes.

Figure 10: Long rough dab in 5a. Length distributions from the spring (upper) and autumn surveys (lower).

Management

The Ministry of Food, Agriculture and Fisheries is responsible for management of the Icelandic fisheries and implementation of legislation. Long rough dab was included in the ITQ system in the 1997/1998 quota year, and as such subjected to TAC limitations, but only in a designated quota area (from Snæfellsnes south and south-east to Stokksnes), the main fishing grounds (Table 3). After considerable decrease in CPUE, direct fishing for long rough dab was no longer commercially viable and the only landings were an incidental catch in other fisheries. In view of the changed situation, the Marine Research Institute (MRI) recommended that the long rough dab caught in the designated quota area should no longer be subjected to TAC limitations after the 2013/2014 quota year.

Table 3: Long rough dab in 5a. Recommended TAC, national TAC set by the Ministry, and landings (tonnes) within the quota area and total landings.
Year Rec. tac National tac Landings from quota area Total landings
1995/1996 5000       6164
1996/1997 5000       5470
1997/1998 5000 5000 3413 3793
1998/1999 5000 5000 3259 3522
1999/2000 5000 5000 2783 3148
2000/2001 5000 5000 2817 3658
2001/2002 5000 5000 2512 3631
2002/2003 5000 5000 2064 3064
2003/2004 5000 5000 1636 2021
2004/2005 5000 5000 772 1026
2005/2006 2000 3500 638 764
2006/2007 500 1500 259 359
2007/2008 500 1000 210 303
2008/2009 250 1000 210 290
2009/2010 200 1000 129 213
2010/2011 200 200 107 193
2011/2012 200 200 77 148
2012/2013 200 200 11 71
2013/2014 200 200 9 89
2014/2015 - - - 50
2015/2016 - - - 14
2016/2017 - - - 17
2017/2018 - - - 22
2018/2019 - - - 29
2019/2020 - - - 24
2020/2021 - - - 22
2021/2022 - - - 57
2022/2023 - - - 81
2023/2024 - - -