Demersal fish

Photo: Frederik Broms, NPI.

Demersal fish 2020
Typography
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Most Barents Sea fish species are demersal (Dolgov et al., 2011); this fish community consists of about 70–90 regularly occurring species, which have been classified into zoogeographic groups. Approximately 25% are either Arctic or mainly Arctic species. The commercial species are boreal or mainly boreal species (Andriashev and Chernova, 1995), except for Greenland halibut (Reinhardtius hippoglossoides) that is classified as either Arcto-boreal (Mecklenburg et al., 2013) or mainly Arctic (Andriashev and Chernova, 1995).

Demersal fish

Distribution maps based on Barents Sea Ecosystem Survey (BESS) data for cod, haddock, long rough dab, Greenland halibut, redfish, and six other demersal fish species can be found at:

http://www.imr.no/tokt/okosystemtokt_i_barentshavet/utbredelseskart/en.

Abundance estimates are available for commercial species that are assessed routinely at the ICES AFWG. Figure 3.7.1 shows such biomass estimates for cod, haddock, and saithe (Pollachius virens) calculated in 2020. Saithe occurs mainly along the Norwegian coast and along the southern coast of the Barents Sea; few occur farther offshore in the Barents Sea itself. Total biomass of these three species peaked in 2010-2013 and has declined since; but remains above the long-term average for the time series dating back to 1960. Greenland halibut and deepwater redfish (Sebastes mentella) are important commercial species with large parts of their distribution within the Barents Sea. Time-series of biomass estimates for deepwater redfish and Greenland halibut are much shorter than those for haddock, cod, and saithe. Other than these main commercial stocks, long rough dab is the demersal stock with the highest biomass. Overall, cod is the dominant demersal species.

Figure 3.7.1 Biomass estimates for cod, haddock, and saithe during the 1960–2020 period from AFWG 2020 (ICES 2020). Note: saithe is only partly distributed in the Barents Sea. Figure 3.7.1 Biomass estimates for cod, haddock, and saithe during the 1960–2020 period from AFWG 2020 (ICES 2020). Note: saithe is only partly distributed in the Barents Sea.

Cod

Young of the year

Estimated abundance of 0-group cod varied from 0.276 billion in 1980 to 464.124 billion individuals in 2014 with a long-term average of 113.727 billion individuals for the 1980-2020 period (Fig. 3.7.2). In 2020, the total abundance index for 0-group cod was lowest observed since 2001 and was 23.595 billion individuals. The distribution of 0-group cod in the Barents Sea was incompletely covered due to lack of coverage in the Russian zone. Based on the average long-term distribution 2000-2017, we corrected the 2018 and 2020 abundance indices for lacking coverage. The corrected abundance index was somewhat higher than the uncorrected and was 40.226 billion individuals in 2020. Therefore, the abundance index of 2020-year class is well below the long-term mean, and thus may be characterized as weak.

Figure 3.7.2. 0-group cod abundance estimates and fluctuation 1980-2020. Orange line shows the long-term average; the blue columns indicates fluctuating abundance; orange columns indicate corrected indices. Note that estimates were calculated in R for the new 15 subareas in the Barents Sea for 2019 and 2020. Abundance indices for cod in 2018 and 2020 were underestimated due to lack of coverage in the eastern Barents Sea. Figure 3.7.2. 0-group cod abundance estimates and fluctuation 1980-2020. Orange line shows the long-term average; the blue columns indicates fluctuating abundance; orange columns indicate corrected indices. Note that estimates were calculated in R for the new 15 subareas in the Barents Sea for 2019 and 2020. Abundance indices for cod in 2018 and 2020 were underestimated due to lack of coverage in the eastern Barents Sea.

Main concentrations of 0-group cod were found in the Great Bank (9.260 billion), South West (6.500 billion) and Thor Iversen Bank (3,262 billion) subregions. In 2020, 0-group cod were larger than in 2019, and were dominated by fish of 6.5 – 8.4 cm length. The largest cod (with an average length > 8.0 cm) were observed in the northern areas, while the smallest cod (with an average length < 5.0 cm) were found close to the Norwegian coast.

Cod one year and older

The northeast Arctic cod stock is currently in good condition, with high total stock size, and high spawning-stock biomass (Fig. 3.7.4). 0-group abundance was very high in the beginning of the last decade (2011–2014); but this has not resulted in strong year classes, as seen from the updated stock-recruitment plot shown in Fig. 3.7.6.

Figure 3.7.4. Cod total stock and spawning stock biomass during the 1946-2020 period, including forecast for 2021. From AFWG (ICES 2020). Figure 3.7.4. Cod total stock and spawning stock biomass during the 1946-2020 period, including forecast for 2021. From AFWG (ICES 2020).

Figure 3.7.5. Cod recruitment at age 3 during the 1950-2019 period and forecast (green) for 2020-2022 (ICES 2020). Figure 3.7.5. Cod recruitment at age 3 during the 1950-2019 period and forecast (green) for 2020-2022 (ICES 2020).

Figure 3.7.6 Spawning stock-recruitment plot for cod cohorts 1946-2017. Cohorts 2010-2017 shown as red dots. Figure 3.7.6 Spawning stock-recruitment plot for cod cohorts 1946-2017. Cohorts 2010-2017 shown as red dots.

Strong 2004- and 2005-year classes have, together with a low fishing mortality, led to rebuilding of the cod stock’s age structure to that observed in the late 1940s (Fig. 3.7.7).

Figure 3.7.7. Age composition of the cod stock (biomass) in 1946, 2000 and 2019. From stock assessment in ICES 2019. Figure 3.7.7. Age composition of the cod stock (biomass) in 1946, 2000 and 2019. From stock assessment in ICES 2019.

Cod expanded the area occupied during the period, as seen from the average distribution for three periods (2004-2009, 2010-2014, and 2015-2019, Fig. 3.7.8). Higher catches of cod were distributed over larger area during the 2004-2009 period, while distribution was limited in the north and northeast Barents Sea. During the 2010-2014 period, higher catches of cod were observed mainly in the north and southeast, while their distribution extended northward and slightly north-eastward. Occupation of larger areas and redistribution of higher catches was most likely influenced by record high stock sizes, dominated by larger and older fish. During the 2015-2019 period, smaller catches of cod were taken in the northern and eastern areas compared to the 2010-2014 period, and the northern limit of the distribution in the area between Spitsbergen and Frans Josef Land was shifted southwards from 2017 to 2019. Since 2004, ice free areas have generally increased in the northern Barents Sea, increasing areas of suitable habitat for cod and allowing record high production. However, a notable decrease in ice-free areas was observed in the winter survey 2019 compared to previous winter surveys, and preliminary reports from the 2020 winter survey indicate a further decrease in 2020. In winter 2021 the ice-covered area in the eastern Barents Sea was larger than in previous years, while there was more open water than usual north of Spitsbergen.

Figure 3.7.8. Distribution of cod catches (kg/nm) during August-September; averaged over periods 2004-2009, 2010-2014, 2015-2019 and in 2020. Figure 3.7.8. Distribution of cod catches (kg/nm) during August-September; averaged over periods 2004-2009, 2010-2014, 2015-2019 and in 2020.

Figure 3.7.9 shows the distribution of cod ≥50cm based on data from the winter survey (January-March during 2008, 2011, and 2019. Note: the survey area was extended northwards in 2014 and coverage is often limited by ice conditions. Cod distribution observed during this survey increased throughout the period, but it is unknown when cod began to inhabit areas north of Bear Island and west of Svalbard during winter.

Figure 3.7.9. Distribution of cod ≥50 cm during winter 2008, 2011, and 2019. Figure 3.7.9. Distribution of cod ≥50 cm during winter 2008, 2011, and 2019.

NEA Haddock

Young of the year

Estimated abundance of 0-group haddock varied from 0.696 billion in 1989 to 98.746 billion individuals in 2005 with a long-term average of 13.293 billion individuals for the 1980-2020 period (Fig. 3.7.11). In 2020, the total abundance estimates for 0-group haddock were 7.161 billion, that was higher than in 2019, while well below the long term mean values observed in the time series. Lack of coverage in the eastern Barents Sea will have minor influence on the level of abundance indices due to 0-group haddock being distributed usually in the western part. Based on the average long-term distribution 2000-2017, we corrected the 2018 and 2020 abundance indices for lacking coverage. The corrected abundance index was somewhat higher than not corrected and was 7.884 billion individuals in 2020. Thus the 2020-year class may be characterized as very weak.

Figure 3.7.11. 0-group haddock abundance estimates and fluctuation 1980-2020. Orange line shows the long-term average; the blue columns indicates fluctuating abundance; orange columns indicate corrected indices. Note that estimates were calculated in R for the new 15 subareas in the Barents Sea for 2019 and 2020. Figure 3.7.11. 0-group haddock abundance estimates and fluctuation 1980-2020. Orange line shows the long-term average; the blue columns indicates fluctuating abundance; orange columns indicate corrected indices. Note that estimates were calculated in R for the new 15 subareas in the Barents Sea for 2019 and 2020.

Haddock one year and older

The Northeast Arctic haddock stock reached record high levels in 2009–2013, due to very strong 2004-2006-year classes. Subsequent recruitment has normalized; the stock remains at a relatively high level and the decline in recent years has now stopped. The abundant 2016-year class may help keeping the stock at this level. (Fig. 3.7.12 and 3.7.13). The large spawning stock did not, until 2016, result in strong year classes (Fig. 3.7.14). It should be noted that the quota (TAC) was not taken in 2020, and that preliminary results from the ecosystem survey in 2020 indicate considerably lower abundance than expected, in particular of older age groups.

Figure 3.7.12. Haddock total stock and spawning stock development during the 1950-2020 period and forecast for 2021 from AFWG (ICES 2020). Figure 3.7.12. Haddock total stock and spawning stock development during the 1950-2020 period and forecast for 2021 from AFWG (ICES 2020).

Figure 3.7.13 Recruitment of haddock during the 1950-2019 period (red) and forecast for 2020-2022 (green) from AFWG (ICES 2020). Figure 3.7.13 Recruitment of haddock during the 1950-2019 period (red) and forecast for 2020-2022 (green) from AFWG (ICES 2020).

Figure 3.7.14. Spawning stock-recruitment plot for haddock cohorts 1950-2017. Cohorts 2010-2017 shown as red dots. Figure 3.7.14. Spawning stock-recruitment plot for haddock cohorts 1950-2017. Cohorts 2010-2017 shown as red dots.

Low catch rates were not evident from the winter survey from 2020 compared to 2019 (Fig. 3.7.15 and 3.7.16).

Figure 3.7.15. Catches from the winter surveys in 2019 and 2020, length groups 20-34cm and 35-49 cm. The average size in winter survey of the strong 2016-year class was 29.7 cm in 2019 in and 36.2 cm in 2020. Figure 3.7.15. Catches from the winter surveys in 2019 and 2020, length groups 20-34cm and 35-49 cm. The average size in winter survey of the strong 2016-year class was 29.7 cm in 2019 in and 36.2 cm in 2020.

The distribution of haddock ≥ 50cm based on winter survey data (January-March) from 2013 (record large spawning stock), 2019, and 2020 are shown in Fig. 3.7.16. Note that the survey area was extended northwards in 2014 and that coverage often is limited by ice extent. Haddock distribution observed during this survey increased during this period, but when haddock began to inhabit areas north of Bear Island and west of Svalbard during winter is unknown.

Figure 3.7.16. Distribution of haddock larger than 50 cm during winter 2013 (year with record high spawning stock biomass), 2019, and 2020. Please note that the survey coverage was extended in 2014. Figure 3.7.16. Distribution of haddock larger than 50 cm during winter 2013 (year with record high spawning stock biomass), 2019, and 2020. Please note that the survey coverage was extended in 2014.

Long rough dab

Young of the year

Estimated abundance of 0-group long rough dab varied from 5 million in 2013 to 6 846 million individuals in 1986 with a long-term average of 661 million individuals for the 1980-2020 period (Fig. 3.7.18). In 2020, the total abundance estimate for 0-group long rough dab were 1 439 million (corresponding to 1.171 thousand tonnes) that was much lower than in 2019, but well above the long-term mean. The 2019-year class was somewhat lower that a record high 1986-year class (Fig. 3.6.18). Even, the abundance index in 2020 was underestimated due to lack of coverage in the eastern Barents Sea, the 2020-year class may be characterized as strong.

Figure 3.7.18. 0-group long rough dab abundance in the Barents Sea during the 1980-2020 period. Orange line shows the long-term average; the blue columns indicates fluctuating abundance. Figure 3.7.18. 0-group long rough dab abundance in the Barents Sea during the 1980-2020 period. Orange line shows the long-term average; the blue columns indicates fluctuating abundance.

The main concentration of 0-group long rough dab was found in the Hopen Deep (1.046 million) subregion, where the smallest fish (with an average length of 2 - 2.4 cm) were observed. Larger fish (an average length 2.5 – 4.0 cm) were observed in Bear Island Trench and Central Bank subareas.

Older long rough dab

Older long rough dab (age 1+) are widely distributed in the Barents Sea. Usually major concentrations of long rough dab are distributed in the central, northern, and eastern parts of the Barents Sea. LRD is a very numerous species. The total number of LRD in the Barents Sea can be more than 5109 individuals (Fig. 3.7.19). Long rough dab abundance estimates based on results from the BESS time-series (August–September) have been relatively stable during the current decade. Many small fish were observed in trawl catches especially in eastern areas during the 2015-2017 BESS. The 2018 index was not calculated due to limited survey coverage in the eastern region of the Barents Sea and in 2019-2020 the index was estimated somewhat above the mean for period 2004-2020. (Fig. 3.7.19).

Figure 3.7.19. Stock numbers and biomass of long rough dab based on BESS data during the 2004–2020 period, calculated using bottom-trawl estimated swept area from BESS. Figure 3.7.19. Stock numbers and biomass of long rough dab based on BESS data during the 2004–2020 period, calculated using bottom-trawl estimated swept area from BESS.

Greenland halibut

Young of the year

In 2020, the total abundance index for 0-group fish were 50.6 million individuals. Estimated biomass was 0.104 thousand tonnes. The abundance indices for 0-group Greenland halibut for 2018 will be re-calculated later and presented in the WGIBAR report in 2022.

Older greenland halibut

The adult component of the stock was, as usual, mainly distributed outside the ecosystem survey area, i.e. on the slope. The abundance on the slope has decreased in recent years (Fig 3.7.20). In recent years, however, an increasing number of large Greenland halibut has been captured in deeper waters of the area surveyed by the BESS (Fig. 3.7.21). Northern and north-eastern areas of the Barents Sea serve as nursery grounds for the stock. Greenland halibut are also relatively abundant in deep channels running between the shallowest fishing banks.

The fishable component of the stock (length ≥45 cm) increased from 1992 to 2012 and has remained stable since that time (Fig. 3.7.22). The harvest rate has been low and relatively stable since 1992.

Figure 3.7.20. Biomass index for Greenland halibut from Norwegian slope survey; 2014 excluded due to poor area coverage. Figure 3.7.20. Biomass index for Greenland halibut from Norwegian slope survey; 2014 excluded due to poor area coverage.

Figure 3.7.21 Greenland halibut distribution (specimens/nautical mile) during August–September 2020 based on the BESS data. Figure 3.7.21 Greenland halibut distribution (specimens/nautical mile) during August–September 2020 based on the BESS data.

Figure 3.7.22. Northeast Arctic Greenland halibut: catches, recruitment, harvest rate and biomass of 45+ cm Greenland halibut as estimated by the GADGET model during the 1992−2018 period (ICES 2019). Figure 3.7.22. Northeast Arctic Greenland halibut: catches, recruitment, harvest rate and biomass of 45+ cm Greenland halibut as estimated by the GADGET model during the 1992−2018 period (ICES 2019).

Deepwater redfish (S. mentella)

Young of the year

Estimated abundance of 0-group deepwater redfish varied from 33 million individuals in 2001 to 1 083 billion in 1985 with an average of 211 billion individuals for the 1980-2020 period (Fig. 3.7.23). In 2020, the total abundance for 0-group deepwater redfish were 526 billion individuals, which is higher than the long-term mean. Thus the 2020-year class may be characterized as a strong. Estimated biomass were also higher than the long-term mean (of 235 thousand tonnes) and was 310 thousand tonnes.

In 2020, 0-group deepwater redfish were distributed mainly in western regions (55.354 billion ind. In Bear Island Trench, 41.360 billion in the South West and 32.192 billion ind. in the Svalbard North Svalbard. Most of largest fish were found in Svalbard North (4.0 - 5.5 cm) and South West (3.5 – 5.0 cm), while some small fish were also observed in South West (1.5 – 3.0 cm).

Figure 3.7.23. 0-group deepwater redfish abundance (corrected for trawl efficiency) in the Barents Sea during 1980-2020. Orange line shows the long-term average; the blue columns indicates annual abundance. Note that the 2018-2020 estimates were calculated in R for the new 15 subareas in the Barents Sea. Figure 3.7.23. 0-group deepwater redfish abundance (corrected for trawl efficiency) in the Barents Sea during 1980-2020. Orange line shows the long-term average; the blue columns indicates annual abundance. Note that the 2018-2020 estimates were calculated in R for the new 15 subareas in the Barents Sea.

Deepwater redfish one year old and older

In 2020, deepwater redfish were widely distributed in the Barents Sea. During the BESS and the winter survey, the largest concentrations were observed, as usual, in western and north western parts of the Barents Sea. Biomass was higher during 2013–2020 than in preceding years. Geographic distribution of deepwater redfish during the 2020 BESS is shown in Fig. 3.7.24. Most of the adult fish are observed in the Norwegian Sea. Stock development trends from the latest ICES AFWG assessment are shown in Fig. 3.7.25. During the last decade, the deepwater redfish total stock biomass has remained relatively stable around 1 million tonnes.

Figure 3.7.24. Geographic distribution of deepwater redfish during the 2020 BESS survey. Figure 3.7.24. Geographic distribution of deepwater redfish during the 2020 BESS survey.

Figure 3.7.25. Catches, recruitment, harvest rate and biomass for S. mentella in ICES Subareas 1 and 2 (ICES, 2020). Figure 3.7.25. Catches, recruitment, harvest rate and biomass for S. mentella in ICES Subareas 1 and 2 (ICES, 2020).

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