Demersal fish

The deepwater redfish (Sebastes mentella) Photo: Fredrik Broms, Norwegian Polar Institute

WGIBAR 2019 - Annex 4: The state and trends of the Barents Sea ecosystem in 2018
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 all 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).

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. Figure 3.6.1 shows biomass estimates for cod, haddock, and saithe (Pollachius virens) from the ICES AFWG assessments conducted in 2018. 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 timeseries dating back to 1960. Greenland halibut and redfish, deepwater redfish (Sebastes mentella) in particular 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 1960–2018 period from AFWG 2018 (ICES 2018c). Note: saithe is only partly distributed in the Barents Sea.Figure 3.6.1 Biomass estimates for cod, haddock, and saithe during the 1960–2018 period from AFWG 2018 (ICES 2018c). Note: saithe is only partly distributed in the Barents Sea.

Cod

Young-of-the-year

Estimated abundance of 0-group cod varied from 276 million in 1980 to 464,124 million individuals in 2014 with a long-term average of 114,452 million individuals for the 1980-2017 period (Figure 3.6.2). In 2018, the total abundance index for 0-group cod was not estimated due to lack of coverage.

Figure 3.6.2. 0-group cod abundance (corrected for trawl efficiency) in the Barents Sea during the 1980–2017 period. Red line shows the long-term average for the 1980–2017 period; the blue line indicates 0-group abundance fluctuation.Figure 3.6.2. 0-group cod abundance (corrected for trawl efficiency) in the Barents Sea during the 1980–2017 period. Red line shows the long-term average for the 1980–2017 period; the blue line indicates 0-group abundance fluctuation.

In 2018, the western Barents Sea (west of the Norwegian-Russian border) was covered and spatial indices were estimated for eight regions (South West, Bear island Trench, Thor Iversen Bank, Hopen Deep, Svalbard South, Svalbard North, Central Bank, and Great Bank (ICES 2018 Annex 4). 0-group cod were distributed mainly in western and central regions (South West, Bear Island Trench, and Thor Iversen Bank) (Figure 3.6.3.). In these eight regions, highest abundance was observed when strong year classes occurred during 2011-2014. Low abundance of 0-group cod was observed in these regions and, thus, it is likely that a strong year class did not occur in 2018.

Figure 3.6.3. Percentage of 0-group cod abundance distributed in western, central, and northern regions of the Barents Sea during the 1980–2018 period. Red line shows total abundance for these eight regions.Figure 3.6.3. Percentage of 0-group cod abundance distributed in western, central, and northern regions of the Barents Sea during the 1980–2018 period. Red line shows total abundance for these eight regions.

Distribution of 0-group cod has varied during the last four decades. and the total area of distribution was smallest during the 1980s and largest during  the current decade. Size of the area occupied was associated with the occurence or  non-occurrence of strong year classes (Figure 3.6.4.).

Figure 3.6.4. Distribution of 0-group cod abundance in the Barents Sea during the 1980s, 1990s, 2000s, and 2010s. Abundance estimates were log-transformed (natural logarithms) before mapping. Fish density varied from low (blue) to high (yellow). Red dots indicated sampling locations. The map is from Eriksen et al. (Progress in Oceanography, under revision).Figure 3.6.4. Distribution of 0-group cod abundance in the Barents Sea during the 1980s, 1990s, 2000s, and 2010s. Abundance estimates were log-transformed (natural logarithms) before mapping. Fish density varied from low (blue) to high (yellow). Red dots indicated sampling locations. The map is from Eriksen et al. (Progress in Oceanography, under revision).

Older cod

The northeast Arctic cod stock is currently in good condition, with high total stock size, and high spawning-stock biomass (Figure 3.6.5). 2004 and 2005 being were strong year classes, subsequent recruitment at age 3 was at an average level (Figure 3.6.6). 0-group abundance has been very high in recent years (2011–2014); but this has not resulted in strong year classes, as seen from the updated stock-recruitment plot shown in Figure 3.6.7.

Figure 3.6.5. Cod total stock and spawning stock biomass during the 1946-2018 period, including forecast for 2019. From AFWG (ICES 2018).Figure 3.6.5. Cod total stock and spawning stock biomass during the 1946-2018 period, including forecast for 2019. From AFWG (ICES 2018).

Figure 3.6.6. Cod recruitment at age 3 during the 1950-2018 period and forecast for 2019-2020 (ICES 2018).Figure 3.6.6. Cod recruitment at age 3 during the 1950-2018 period and forecast for 2019-2020 (ICES 2018).

Figure 3.6.7 Spawning stock recruitment plot for cod cohorts 1946-2014 period. Cohorts 2010-2014 shown as black dots.Figure 3.6.7 Spawning stock recruitment plot for cod cohorts 1946-2014 period. Cohorts 2010-2014 shown as black 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 3.6.8).

Figure 3.6.8. Age composition of the cod stock  (biomass) during periods between 1946 and 2018. From data in ICES 2018.Figure 3.6.8. Age composition of the cod stock (biomass) during periods between 1946 and 2018. From data in ICES 2018.

Cod expanded the area occupied during the period, as seen from the average distribution for three periods (2004-2009, 2010-2014, and 2015-2017, Figure 3.6.9). 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 2015-2017 period, smaller catches of cod were taken and the area of occupation decreased slightly compared to the 2010-2014 period. 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.

Figure 3.6.9. Distribution of cod catches (kg/nm) during August-September; averaged over 3 periods (2004-2009, 2010-2014, and 2015-2017).Figure 3.6.9. Distribution of cod catches (kg/nm) during August-September; averaged over 3 periods (2004-2009, 2010-2014, and 2015-2017).

Figure 3.3.10 show the distribution of cod ≥50cm based on data from the BESS (January-March during 2008, 2011, and 2018. 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 3.6.10. Distribution of cod larger than 50 cm during winter 2008, 2011, and 2018.Figure 3.6.10. Distribution of cod larger than 50 cm during winter 2008, 2011, and 2018.

It should also be noted that during summer/autumn 2018 fishable concentrations of large cod (> 65 cm) were observed in the Jan Mayen area by a Norwegian long-liner; 450 tonnes were caught in total. This is a new development. As late as 2011, very low cod abundance (only 19 specimens in 9 trawl hauls) was observed during a survey in the area. Analyses of both otolith pattern and genetics showed this specimen to be a hybrid of Barents Sea and Icelandic cod. An exploratory fishery will be conducted in this area during each quarter of 2019 to further investigate the spatial and temporal variation of cod in this area. Biological sampling and tagging will be carried out.

NEA haddock

Young-of-the-year

Estimated abundance of 0-group haddock varied from 75 million in 1981 to 91,606 million individuals in 2005 with a long-term average of 11,740 million individuals for the 1980-2017 period (Figure 3.6.11). In 2018, the total abundance index for 0-group haddock was not estimated due to lack of coverage.

Figure 3.6.11. 0-group haddock abundance, corrected for trawl efficiency, in the Barents Sea 1980–2017. Red line shows long-term mean for the period 1980–2017, while the blue line indicates 0-group abundance fluctuation.Figure 3.6.11. 0-group haddock abundance, corrected for trawl efficiency, in the Barents Sea 1980–2017. Red line shows long-term mean for the period 1980–2017, while the blue line indicates 0-group abundance fluctuation.

In 2018, the western Barents Sea (west of the Norwegian-Russian border) was covered, and spatial indices were estimated for eight regions (South West, Bear Island Trench, Thor Iversen Bank, Hopen Deep, Svalbard South, Svalbard North, Central Bank, and Great Bank (ICES 2018 Annex). 0-group haddock were distributed mainly in western regions (South West and Bear Island Trench) (Figure 3.6.12). Highest abundance in these eight regions was observed in 2005, a year of record high 0-group abundance, and in 2009, when a very strong year class occurred. Low abundance of 0-group haddock in 2018 indicates that a strong year class did not occur.

Figure 3.6.12. Percentages of 0-group haddock abundance in the South West, Bear Island Trench, Thor Iversen Bank, Hopen Deep, Svalbard South, and Svalbard North during the 1980–2018 period in the Barents Sea. More details about these spatial indices is given in ICES 2018 Annex 4.Figure 3.6.12. Percentages of 0-group haddock abundance in the South West, Bear Island Trench, Thor Iversen Bank, Hopen Deep, Svalbard South, and Svalbard North during the 1980–2018 period in the Barents Sea. More details about these spatial indices is given in ICES 2018 Annex 4.

During the last four decades 0-group haddock   have been distribution in the western and central Barents Sea. The smallest area of occupation was observed in the 1980s, and has since increased. Size of area occupied was assosiated with year-class strength (Figure 3.6.13).

Figure 3.6.13. Distribution of 0-group haddock abundance in the Barents Sea during the 1980s, 1990s, 2000s, and 2010s. Abundance estimates were log-transformed (natural logarithms) before mapping. Fish density varied from low (blue) to high (yellow). Red dots indicated sampling locations. The map is from Eriksen et al. (Progress in Oceanography, under revision).Figure 3.6.13. Distribution of 0-group haddock abundance in the Barents Sea during the 1980s, 1990s, 2000s, and 2010s. Abundance estimates were log-transformed (natural logarithms) before mapping. Fish density varied from low (blue) to high (yellow). Red dots indicated sampling locations. The map is from Eriksen et al. (Progress in Oceanography, under revision).

Older haddock

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 abundant 2016 and 2017 year classes may increase stock size rapidly in future years if survival is good. (Figures 3.6.14 and 3.6.15). The large spawning stock did not, until 2014, result in strong year classes (Figure 3.6.16).

Figure 3.6.14. Haddock total stock and spawning stock development during the 1950-2018 period and forecast for 2019 from AFWG (ICES 2018).Figure 3.6.14. Haddock total stock and spawning stock development during the 1950-2018 period and forecast for 2019 from AFWG (ICES 2018).

 Figure 3.6.15 Recruitment of haddock during the 1950-2018 period and forecast for 2019-2020 from AFWG (ICES 2018). Figure 3.6.15 Recruitment of haddock during the 1950-2018 period and forecast for 2019-2020 from AFWG (ICES 2018).

Figure 3.6.16. Spawning stock-recruitment plot for haddock cohorts 1950-2014. Cohorts 2010-2014 shown as black dots. Figure 3.6.16. Spawning stock-recruitment plot for haddock cohorts 1950-2014. Cohorts 2010-2014 shown as black dots.

Figure 3.6.17. Distribution of haddock catches (kg/nm) during August-September averaged over 3 periods (2004-2009, 2010-2014, and 2015-2017). Figure 3.6.17. Distribution of haddock catches (kg/nm) during August-September averaged over 3 periods (2004-2009, 2010-2014, and 2015-2017).

The distribution area of haddock expanded in the southeast from 2004 onwards (Figure 3.6.17). Figure 3.6.18 shows the distribution of haddock ≥ 50cm based on BESS data (January-March) from 2008, 2011, and 2018. 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 3.6.18. Distribution of haddock larger than 50 cm during winter 2008, 2011, and 2018. Figure 3.6.18. Distribution of haddock larger than 50 cm during winter 2008, 2011, and 2018.

Long rough dab

Young of the year

An abundance index for 0-group fish is available for 2018 due to a lack of survey coverage. Figure 3.6.19 shows the time series for the 1980-2017 period.

Figure 3.6.19. 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 3.6.19. 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. During the Russian Autumn-Winter Survey (October-December) and the BESS (August–September), major concentrations of long rough dab were observed in the central, northern, and eastern areas.  Many small fish were observed in trawl catches especially in eastern areas during the 2015-2017 BESS. This is agrees with the CPUE index from the Russian Autumn-Winter Survey, which in 2017 was twice as high as the long-term average. It is difficult to track trends with this index, however; in 2016 and 2018 the survey was not performed, and in 2017 it 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). Long rough dab abundance estimates based on results from the BESS time-series have been relatively stable during the current decade. The 2018 index was not calculated due to limited survey coverage in the eastern region of the Barents Sea. (Figure 3.6.21).

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

Figure 3.6.21. Stock biomass of long rough dab based on BESS data during the 2005–2017 period, calculated using bottom-trawl estimated swept area. Figure 3.6.21. Stock biomass of long rough dab based on BESS data during the 2005–2017 period, calculated using bottom-trawl estimated swept area.

Greenland halibut

Young of the year

The2018 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. 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. Figure 3.6.23 shows an index for Greenland halibut at the nursery grounds based on the BESS results north of 76.5°N, from northwest of Svalbard and east to Franz Josef Land (for details see Hallfredsson and Vollen 2015, WD 1 ICES IBPhali 2015).
The fishable component of the stock (length ≥45 cm) increased from 1992 to 2012 and has remained stable since that time (Figure 3.6.24). The harvest rate has been low and relatively stable since 1992.

Figure 3.6.22 Greenland halibut distribution (specimens/nautical mile) during August–September 2018 based on the BESS data. Figure 3.6.22 Greenland halibut distribution (specimens/nautical mile) during August–September 2018 based on the BESS data.

Figure 3.6.23. Biomass index for Greenland halibut at nursery areas; 2014 excluded due to poor area coverage.Figure 3.6.23. Biomass index for Greenland halibut at nursery areas; 2014 excluded due to poor area coverage.

Figure 3.6.24. Northeast Arctic Greenland halibut: numbers (upper left);  biomass (upper right) for 45+ cm Greenland halibut as estimated by the GADGET model; and estimated exploitation rates (lower center) during the 1992−2016 period (ICES 2017).Figure 3.6.24. Northeast Arctic Greenland halibut: numbers (upper left); biomass (upper right) for 45+ cm Greenland halibut as estimated by the GADGET model; and estimated exploitation rates (lower center) during the 1992−2016 period (ICES 2017).

Deepwater redfish

Young-of-the-year

Estimated abundance of 0-group deepwater redfish varied from 6 million individuals in 2001 to 156,548 million in 2007 with an average of 60,307 million individuals for the 1980-2017 period (Figure 3.6.25). In 2018, the total abundance index for 0-group deepwater redfish were not estimated due to lack of survey coverage.

Figure 3.6.25. 0-group deepwater redfish abundance (corrected for trawl efficiency) in the Barents Sea during the 1980–2017 period. Red line shows the long-term average, while the blue line indicates 0-group abundance fluctuation.Figure 3.6.25. 0-group deepwater redfish abundance (corrected for trawl efficiency) in the Barents Sea during the 1980–2017 period. Red line shows the long-term average, while the blue line indicates 0-group abundance fluctuation.

In 2018, the western Barents Sea (west of the Norwegian-Russian border) was covered and spatial indices were estimated for eight regions (South West, Bear Island Trench, Thor Iversen Bank, Hopen Deep, Svalbard South, Svalbard North, Central Bank, and Great Bank (ICES 2018 Annex 4). 0-group deepwater redfish were distributed mainly in regions of Svalbard (South West, Bear Island Trench, Svalbard South, and Svalbard North (Figure 3.6.26). Highest abundance in these eight regions was observed in years with strong year classes: 1980, 1985, and 2007.  During the last 5 years, deepwater redfish have mainly been observed in Svalbard South and Svalbard North.

Figure 3.6.26. Percentage of 0-group deepwater redfish abundance in western, central, and northern regions of the Barents Sea during the 1980–2018 period. Red line shows total abundance for these eight regions.Figure 3.6.26. Percentage of 0-group deepwater redfish abundance in western, central, and northern regions of the Barents Sea during the 1980–2018 period. Red line shows total abundance for these eight regions.

Distribution of 0-group deepwater redfish has varied during the last four decades: it was largest during the 1980s; decreased during next two decades; and has increased during the 2010s (Figure 3.6.27). Size of area occupied was associated with occurence or  non-occurrence of strong year classes.

Figure 3.6.27. Distribution of 0-group deepwater redfish abundance in the Barents Sea during 1980s, 1990s, 2000s, and 2010s. Abundance estimates were log-transformed (natural logarithms) before mapping. Fish density varied from low (blue) to high (yellow). Red dots indicated sampling locations. The map is taken from Eriksen et al. (Progress in Oceanography, under revision).Figure 3.6.27. Distribution of 0-group deepwater redfish abundance in the Barents Sea during 1980s, 1990s, 2000s, and 2010s. Abundance estimates were log-transformed (natural logarithms) before mapping. Fish density varied from low (blue) to high (yellow). Red dots indicated sampling locations. The map is taken from Eriksen et al. (Progress in Oceanography, under revision).

Older deepwater redfish

In 2018, deepwater redfish were widely distributed in the Barents Sea. During the BESS and the winter survey, largest concentrations were observed, as usual, in western and north western parts of the Barents Sea. Biomass was higher during 2013–2018 than in preceding years. Geographic distribution of deepwater redfish during the 2018 BESS is shown in Figure 3.6.28. The area of coverage for redfish during BESS 2018 was almost complete. Most adult fish are observed in the Norwegian Sea. Stock development trends from the latest ICES AFWG assessment are shown in Figure 3.6.29.  During the current decade the deepwater redfish stock biomass has remained relatively stable and varied around 1 million tonnes.

Figure 3.6.28. Geographic distribution of deepwater redfish during the 2018 BESS survey.Figure 3.6.28. Geographic distribution of deepwater redfish during the 2018 BESS survey.

Figure 3.6.29. Results from a statistical catch-at-age model showing trends in total stock biomass (TSB) (‘000s), spawning-stock biomass (SSB) and recruitment-at-age 2 (millions of individuals)  during the 1992–2017 period for S. mentella in ICES Subareas 1 and 2 (ICES, 2018).Figure 3.6.29. Results from a statistical catch-at-age model showing trends in total stock biomass (TSB) (‘000s), spawning-stock biomass (SSB) and recruitment-at-age 2 (millions of individuals) during the 1992–2017 period for S. mentella in ICES Subareas 1 and 2 (ICES, 2018).

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