Demersal fish

Photo: Ann K. Balto, Norwegian Polar Institute..

Demersal fish 2019
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, 1994).

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 3.6.1 shows such biomass estimates for cod, haddock, and saithe (Pollachius virens) calculated in 2019. 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 3.6.1 Biomass estimates for cod, haddock, and saithe during the 1960–2019 period from AFWG 2019 (ICES 2019a). Note: saithe is only partly distributed in the Barents Sea. Figure 3.6.1 Biomass estimates for cod, haddock, and saithe during the 1960–2019 period from AFWG 2019 (ICES 2019a). Note: saithe is only partly distributed in the Barents Sea.

Cod

Young of the year

Estimated abundance of 0-group cod varied from 325 million in 1981 to 614,744 million individuals in 2014 with a long-term average of 139,460 million individuals for the 1980-2019 period (Figure 3.6.2). In 2018, the total abundance index for 0-group cod was not estimated due to lack of coverage. In 2019, the total abundance index for 0-group cod was 23,404 million individuals.

Figure 3.6.2. 0-group cod abundance estimates and fluctuation 1980-2019. Note that estimates were calculated for the new 15 subareas in the Barents Sea for the period of 1980-2018 in MatLab (ICES 2018), while for 2019 estimates were calculated using StoX (Johansen et al. 2019).    Figure 3.6.2. 0-group cod abundance estimates and fluctuation 1980-2019. Note that estimates were calculated for the new 15 subareas in the Barents Sea for the period of 1980-2018 in MatLab (ICES 2018), while for 2019 estimates were calculated using StoX (Johansen et al. 2019).

In 2019, the distribution of 0-group cod in the Barents Sea was covered well and abundance indices were estimated. The abundance index of 2019 year class is well below the long-term mean, and thus may be characterized as weak. 0-group cod were widely distributed on the surveyed area, except northern and south-eastern areas. The main dense concentrations were found in the South West area (Figure 3.6.3.). In 2019, 0-group cod was dominated by fish of 5 - 7.5 cm length. The largest cod (with an average length of 8.0 cm) were observed in the Central Bank, Svalbard South and Svalbard North areas, while smallest cod (with an average length of 5.1 cm) were found in the North East.

Figure 3.6.3. Percentage of 0-group cod abundance distributed by different regions of the Barents Sea during the 1980-2019. Note that estimates were calculated for the new 15 subareas in the Barents Sea for the period 1980-2018 in MatLab (ICES 2018 WGIBAR), while for 2019 using StoX (Johnsen et al. 2019). Figure 3.6.3. Percentage of 0-group cod abundance distributed by different regions of the Barents Sea during the 1980-2019. Note that estimates were calculated for the new 15 subareas in the Barents Sea for the period 1980-2018 in MatLab (ICES 2018 WGIBAR), while for 2019 using StoX (Johnsen et al. 2019).

Cod one year old and older

The northeast Arctic cod stock is currently in good condition, with high total stock size, and high spawning-stock biomass (Figure 3.6.4). Strong 2004- and 2005-year classes were estimated as average at age 3 (Figure 3.6.5). 0-group abundance has been 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 Figure 3.6.6.

Figure 3.6.4. Cod total stock and spawning stock biomass during the 1946-2019 period, including forecast for 2020-2021. From AFWG (ICES 2019a). Figure 3.6.4. Cod total stock and spawning stock biomass during the 1946-2019 period, including forecast for 2020-2021. From AFWG (ICES 2019a).

Figure 3.6.5. Cod recruitment at age 3 during the 1950-2018 period and forecast for 2019-2021 (ICES 2019). Figure 3.6.5. Cod recruitment at age 3 during the 1950-2018 period and forecast for 2019-2021 (ICES 2019).

Figure 3.6.6 Spawning stock-recruitment plot for cod cohorts 1946-2015. Cohorts 2010-2015 shown as red dots. Figure 3.6.6 Spawning stock-recruitment plot for cod cohorts 1946-2015. Cohorts 2010-2015 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 (Figure 3.6.7).

Figure 3.6.7. Age composition of the cod stock (biomass) in 1946, 2000 and 2019. From stock assessment in ICES 2019. Figure 3.6.7. 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, Figure 3.6.8). 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.

Figure 3.6.8. Distribution of cod catches (kg/nm) during August-September; averaged over 3 periods (2004-2009, 2010-2014, and 2015-2019). Figure 3.6.8. Distribution of cod catches (kg/nm) during August-September; averaged over 3 periods (2004-2009, 2010-2014, and 2015-2019).

Figure 3.6.9 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 3.6.9. Distribution of cod ≥50 cm during winter 2008, 2011, and 2019. Figure 3.6.9. 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 696 million in 1989 to 98,745 million individuals in 2005 with a long-term average of 13,440 million individuals for the 1980-2019 period (Figure 3.6.11). In 2019, the total abundance estimates for 0-group haddock were 892 million, that it is one of the lowest values observed in the time series. Thus the 2019-year class may be characterized as very weak.

Figure 3.6.11. 0-group haddock abundance estimates and fluctuation in 1980-2019. Note that estimates were calculated for the new 15 subareas in the Barents Sea for the period 1980-2018 in MatLab (ICES 2018 WGIBAR), while for 2019 estimates were calculated using StoX (Johnsen et al. 2019).  Figure 3.6.11. 0-group haddock abundance estimates and fluctuation in 1980-2019. Note that estimates were calculated for the new 15 subareas in the Barents Sea for the period 1980-2018 in MatLab (ICES 2018 WGIBAR), while for 2019 estimates were calculated using StoX (Johnsen et al. 2019).

In 2019, 0-group haddock in the Barents Sea was covered well, and spatial indices were estimated for all regions. 0-group haddock were distributed mainly in western regions (Svalbard South and Bear Island Trench, Figure 3.6.12). Haddock length varied from 2.5 to 13.5 cm, while the length distribution was dominated by haddock of 8.5-10.5 cm length. The smallest haddock were found in South West, while the largest was found in the Great Bank area.

Figure 3.6.12. Percentage of 0-group haddock abundance distributed by different regions of the Barents Sea during 1980-2019. Note that estimates were calculated for the new 15 subareas in the Barents Sea for the period 1980-2018 in MatLab (ICES 2018 WGIBAR), while for 2019 the estimates using StoX (Johansen et al. 2019). Figure 3.6.12. Percentage of 0-group haddock abundance distributed by different regions of the Barents Sea during 1980-2019. Note that estimates were calculated for the new 15 subareas in the Barents Sea for the period 1980-2018 in MatLab (ICES 2018 WGIBAR), while for 2019 the estimates using StoX (Johansen et al. 2019).

Haddock one year old 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 but has declined in recent years. Forecasts based on survey indices indicate that the abundant 2016- and 2017-year classes may increase stock size rapidly in future years if survival is good. (Figures 3.6.13 and 3.6.14). The large spawning stock did not, until 2016, result in strong year classes (Figure 3.6.15).

Figure 3.6.13. Haddock total stock and spawning stock development during the 1950-2019 period and forecast for 2020-2021 from AFWG (ICES 2019a). Figure 3.6.13. Haddock total stock and spawning stock development during the 1950-2019 period and forecast for 2020-2021 from AFWG (ICES 2019a).

Figure 3.6.14 Recruitment of haddock during the 1950-2018 period (red) and forecast for 2019-2021 (green) from AFWG (ICES 2019a). Figure 3.6.14 Recruitment of haddock during the 1950-2018 period (red) and forecast for 2019-2021 (green) from AFWG (ICES 2019a).

Figure 3.6.15. Spawning stock-recruitment plot for haddock cohorts 1950-2015. Cohorts 2010-2015 shown as red dots. Figure 3.6.15. Spawning stock-recruitment plot for haddock cohorts 1950-2015. Cohorts 2010-2015 shown as red dots.

Occurrence of the very strong 2004-2006-year classes led to higher catches in the western and coastal areas. During the last two periods (2010-2014 and 2015-2019) haddock was distributed in the same areas but in much lower amounts (Figure 3.6.16).

Figure 3.6.16. Distribution of haddock catches (kg/nm) during August-September averaged over 3 periods (2004-2009, 2010-2014, and 2015-2019). Figure 3.6.16. Distribution of haddock catches (kg/nm) during August-September averaged over 3 periods (2004-2009, 2010-2014, and 2015-2019).

Figure 3.6.17 shows the distribution of haddock ≥ 50cm based on winter survey data (January-March) from 2008, 2011, and 2019. 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 3.6.17. Distribution of haddock larger than 50 cm during winter 2008, 2011, and 2019. Figure 3.6.17. Distribution of haddock larger than 50 cm during winter 2008, 2011, and 2019.

Long rough dab

Young of the year

No abundance index for 0-group fish is available for 2018 due to a lack of survey coverage. Figure 3.6.18 shows the time series for the 1980-2017 period.

Figure 3.6.18. 0-group long rough dab abundance in the Barents Sea during the 1980-2017 period corrected for trawl efficiency. Red line shows the long-term average; the blue line indicates fluctuating abundance. Figure 3.6.18. 0-group long rough dab abundance in the Barents Sea during the 1980-2017 period corrected for trawl efficiency. Red line shows the long-term average; the blue line indicates fluctuating abundance.

Older long rough dab

Older long rough dab (age 1+) are widely distributed in the Barents Sea. 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 index estimated abundance somewhat above mean for period 2004-2017. (Figure 3.6.19).

Figure 3.6.19. Stock biomass of long rough dab based on BESS data during the 2004–2019 period, calculated using bottom-trawl estimated swept area. Figure 3.6.19. Stock biomass of long rough dab based on BESS data during the 2004–2019 period, calculated using bottom-trawl estimated swept area.

Previously during the Russian Autumn-Winter Survey (October-December) major concentrations of long rough dab in the central, northern, and eastern areas were found. The catch-per-unit-effort index (CPUE) from this survey was calculated as number of specimens caught per 1 hour of trawling. For period 1982-2015 the index ranged from 30 to 120, amounting to 90 specimens per 1 hour of trawling on average. In 2017 values twice as high as the long-term average were found as the survey was performed in a limited area where the main concentration of young long rough dab occurred. Excluding areas with low fish concentrations in calculations can lead to overestimates in this index (Figure 3.6.20). It is difficult to track trends with this index, because in 2016 and in 2018 -2019 the survey was not performed.

Figure 3.6.20. Estimated of long rough dab from the Russian Autumn-Winter Survey (October-December) during the 1982–2019 period. No survey coverage in 2016 and 2018-2019 and limited survey coverage in 2017. Figure 3.6.20. Estimated of long rough dab from the Russian Autumn-Winter Survey (October-December) during the 1982–2019 period. No survey coverage in 2016 and 2018-2019 and limited survey coverage in 2017.

Greenland hlibut

young of the year

The 2018 index for 0-group fish is not available due to lack of survey coverage

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 3.6.21). In recent years, however, an increasing number of large Greenland halibut has been captured in deeper waters of the area surveyed by the BESS (Figure 3.6.22). 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 (Figure 3.6.23). The harvest rate has been low and relatively stable since 1992.

Figure 3.6.21. Biomass index for Greenland halibut from Norwegian slope survey; 2014 excluded due to poor area coverage (update of ICES 2019a fig 8.7) Figure 3.6.21. Biomass index for Greenland halibut from Norwegian slope survey; 2014 excluded due to poor area coverage (update of ICES 2019a fig 8.7)

Figure 3.6.22 Greenland halibut distribution (specimens/nautical mile) during August–September 2019 based on the BESS data. Figure 3.6.22 Greenland halibut distribution (specimens/nautical mile) during August–September 2019 based on the BESS data.

Figure 3.6.23. 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 2019a). Figure 3.6.23. 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 2019a).

Beaked (deepwater) redfish (S. mentella)

Young of the year

Estimated abundance of 0-group deepwater redfish varied from 9 million individuals in 2001 to 191,145 million in 2007 with an average of 53,355 million individuals for the 1980-2019 period (Figure 3.6.24). In 2019, the total abundance index for 0-group deepwater redfish were 91,065 million individuals, which is higher than the long-term mean. Thus the 2019-year class may be characterized as close to strong.

Figure 3.6.24. 0-group deepwater redfish abundance (corrected for trawl efficiency) in the Barents Sea during 1980-2019. Note that estimates were calculated for the new 15 subareas in the Barents Sea for the period 1980-2018 in MatLab (ICES 2018 WGIBAR), while for 2019 they were calculated using StoX (Johnsen et al. 2019). Figure 3.6.24. 0-group deepwater redfish abundance (corrected for trawl efficiency) in the Barents Sea during 1980-2019. Note that estimates were calculated for the new 15 subareas in the Barents Sea for the period 1980-2018 in MatLab (ICES 2018 WGIBAR), while for 2019 they were calculated using StoX (Johnsen et al. 2019).

In 2019, 0-group deepwater redfish were distributed mainly in regions of Svalbard (Svalbard South and Bear Island Trench, Figure 3.6.25). The deepwater redfish were 3.9 cm long (on average). The largest fish with average length 4.6 cm were observed in Svalbard North, while smallest with an average of 2.1 cm in the South West.

Figure 3.6.25. Percentage of 0-group deepwater redfish abundance in the Barents Sea during 1980-2019. Note that estimates were calculated for the new 15 subareas in the Barents Sea for the period 1980-2018 in MatLab (ICES 2018 WGIBAR), while for 2019 they were calculated using StoX (Johansen et al. 2019). Figure 3.6.25. Percentage of 0-group deepwater redfish abundance in the Barents Sea during 1980-2019. Note that estimates were calculated for the new 15 subareas in the Barents Sea for the period 1980-2018 in MatLab (ICES 2018 WGIBAR), while for 2019 they were calculated using StoX (Johansen et al. 2019).

Beaked redfish one year old and older

In 2019, 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 2013–2019 than in preceding years. Geographic distribution of deepwater redfish during the 2019 BESS is shown in Figure 3.6.26. The area of coverage for redfish during BESS 2019 was complete in the north and east. Most of the adult fish are observed in the Norwegian Sea. Stock development trends from the latest ICES AFWG assessment are shown in Figure 3.6.27. During the last decade the deepwater redfish total stock biomass has remained relatively stable around 1 million tonnes. From 1992 to 2002, there was an increase in the total stock, then, from 2003 to 2011, its stabilization, and in 2012-2018 - further growth, which has slowed in the last 3 years. Spawning stock increased in the period from 1992 to 2007, then it declined until 2013. Over the past 5 years, the biomass of spawning stock has stabilized. The decrease in spawning stock was due to poor year-classes of 1996-2003. Year classes of 2011-2016 were estimated as below average, but above the poor year-classes of 1996-2003.

Figure 3.6.26. Geographic distribution of deepwater redfish during the 2019 BESS survey. Figure 3.6.26. Geographic distribution of deepwater redfish during the 2019 BESS survey.

Figure 3.6.27. Results from a statistical catch-at-age model showing trends in total stock biomass (TSB) (1000 tonnes), spawning-stock biomass (SSB, 1000 tonnes) and recruitment-at-age 2 (individuals) during the 1992–2018 period for beaked redfish in ICES Subareas 1 and 2 (ICES, 2019a). Figure 3.6.27. Results from a statistical catch-at-age model showing trends in total stock biomass (TSB) (1000 tonnes), spawning-stock biomass (SSB, 1000 tonnes) and recruitment-at-age 2 (individuals) during the 1992–2018 period for beaked redfish in ICES Subareas 1 and 2 (ICES, 2019a).

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