Demersal fish

The deepwater redfish (Sebastes mentella). Photo: Norwegian Polar Institute

WGIBAR 2018 - Annex 5: The state and trends of the Barents Sea ecosystem in 2017
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 zoogeographical groups. About 25% are Arctic or mainly Arctic species. The commercial species are all boreal or mainly boreal (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 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, and are based on data from the BESS.

Abundance estimates are available for the commercial species that are assessed. Fig. 3.6.1 shows biomass of cod, haddock, and saithe (Pollachius virens) from the ICES AFWG assessments made in 2017. Saithe occurs mainly along the Norwegian coast and off the coast south of the Barents Sea; few accur in the Barents Sea itself. Total biomass of these three species is close to the highest recorded in time series dating back to 1960. Greenland halibut and redfish, in particular S. mentella, are important commercial species with large part of their distribution within the Barents Sea. Time series of biomass estimates for S. mentella 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.

Fig.3.6.1 Biomass estimates of cod, haddock and saithe 1960-2017 from AFWG 2016 (ICES 2017c). Please note that saithe is only partly distributed in the Barents Sea.Fig.3.6.1 Biomass estimates of cod, haddock and saithe 1960-2017 from AFWG 2016 (ICES 2017c). Please note that saithe is only partly distributed in the Barents Sea.

Cod

Young of the year

0-group cod were widely distributed within the 2017 surveyed area. The main dense concentrations were observed in the central part of the Barents Sea. The 2017 cod abundance index is underestimated as the north-eastern region was not covered.estimated 0-group cod biomass (961 thousand tonnes) is higher than for 2015 and 2016 and higher than the long-term mean (618 thousand tonnes). The abundance index for the 2017-year class is twice the long term mean, and may be characterized as strong (Fig. 3.6.2). Lengths of 0-group cod were between 4 and 14.4 cm; with a mean length of 8.3 cm, higher than the long term (7.6 cm). Most fish (89%) were between 7.0 and 9.9 cm; indicating good growth, and sufficient feeding and living conditions during the first summer.

Figure 3.6.2. 0-group cod abundance, corrected for trawl efficiency, in the Barents Sea 1980-2017. Red line shows the long term mean for the period 1980-2017, while the blue line indicates 0-group abundance fluctuation.Figure 3.6.2. 0-group cod abundance, corrected for trawl efficiency, in the Barents Sea 1980-2017. Red line shows the long term mean for the period 1980-2017, while the blue line indicates 0-group abundance fluctuation.

Older cod

The Northeast Arctic cod stock is currently in good condition, with high total stock size, and spawning stock biomass (Fig. 3.6.3). The 2004 and 2005 year classes were very strong, but subsequent recruitment at age 3 returned to an average level (Fig. 3.6.4). 0-group abundance has been very high in recent years (2011-2014); but thus far, this has not resulted in strong year classes.

Figure 3.6.3. Cod total stock and spawning stock development – from AFWG 2017 (ICES 2017c).Figure 3.6.3. Cod total stock and spawning stock development – from AFWG 2017 (ICES 2017c).

Fig. 3.6.4. Cod recruitment at age 3 from AFWG 2017 (ICES 2017c).Fig. 3.6.4. Cod recruitment at age 3 from AFWG 2017 (ICES 2017c).

The strong 2004 and 2005-year classes have, together with a low fishing mortality, led to rebuilding of the cod age structure to that seen in the late 1940s (Fig. 3.6.5).

Fig. 3.6.5. Cod age group distribution (biomass). From data in ICES 2017c.Fig. 3.6.5. Cod age group distribution (biomass). From data in ICES 2017c.

NEA haddock

Young of the year

In 2017, haddock had relatively wide distribution in the western, central, and north-western areas of the Barents Sea. Haddock biomass was 258 thousand tonnes; close to the 2016 estimate, and higher than the 1993-2017 long-term mean (176 thousand tonnes). Estimated 0-group abundance is 1.7 times higher than the long-term mean; the 2017 year class can be characterized as strong (Fig. 3.6.6). The length of 0-group haddock varied between 4.5 and 16.9 cm, with an average of 10.7 cm; most fish (61%) had lengths between 9.0 and 11.9 cm; indications are that young haddock had suitable living conditions in 2017.

Figure  3.6.6. 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 3.6.6. 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.

Older haddock

The Northeast Arctic haddock stock reached record levels in 2009-2013, due to the very strong 2004-2006-year classes. Subsequently, recruitment has normalized; the stock is still at a relatively high level, but has declined in recent years (Fig. 3.6.7 and 3.6.8).

Figure 3.6.7. Haddock total stock and spawning stock development – from AFWG 2017 (ICES 2017c).Figure 3.6.7. Haddock total stock and spawning stock development – from AFWG 2017 (ICES 2017c).

Figure 3.6.8 Recruitment of haddock (ICES 2017c).Figure 3.6.8 Recruitment of haddock (ICES 2017c).

Long rough dab

Young of the year

In 2017, 0-group long rough dab were observed at survey boundary areas. The largest catches were taken in the south-eastern Barents Sea. Some 0-group individuals were taken by bottom trawl; this indicates that settlement to the bottom has begun, and that abundance indices will be slightly underestimated in 2017. The long rough dab index was the lowest since 2014, and lower than the long-term mean (Fig. 3.6.9). Fish length varied between 1.0 and 5.4 cm, with a mean length of 2.9 cm; this was lower than the long-term average (3.3 cm).

Figure 3.6.9. 0-group long rough dab 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 3.6.9. 0-group long rough dab 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.

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 and were dominated by numbers in the bottom trawl catches in surveys. Many small fish were observed in trawl catches especially in the eastern areas at the 2015-2016 BESS. Long rough dab abundance has been somewhat stable over last decade according to both the Russian Autumn-Winter Survey and the BESS time series (Fig 3.6.10 and 3.6.11).

Figure 3.6.10. Catch-per-unit-effort of long rough dab at the Russian Autumn-Winter Survey 1982-2015 (October-December). <em>*2016 – no survey</em>Figure 3.6.10. Catch-per-unit-effort of long rough dab at the Russian Autumn-Winter Survey 1982-2015 (October-December). *2016 – no survey

Figure 3.6.11. Stock biomass of long rough dab during the 2005-2017 BESS, calculated using bottom trawl estimates (swept area).Figure 3.6.11. Stock biomass of long rough dab during the 2005-2017 BESS, calculated using bottom trawl estimates (swept area).

Greenland halibut

Young of the year

Since 2005, only low concentrations of 0-group Greenland halibut were found. In 2017, they were observed north and south of the Svalbard/Spitsbergen where only few small catches were taken. The BESS survey does not cover the numerous Svalbard/Spitsbergen fjords, where 0-group Greenland halibut are abundant; therefore, this index does not reliably reflect recruitment to the stock at age 0; however, it may reflect the minimum abundance of the year-class strength in the standard long term surveyed area. During 2012-2017, abundance of Greenland halibut continuously declined, the 2017-year class index is also low. Fish length varied between 6 and 8.9 cm, while most fish (67%) were between 7.5 and 8.4 cm. The mean length was 7.7 cm; higher than the long term mean (6.3 cm).

Older Greenland halibut

The adult component of the stock was, as usual, mainly distributed outside the ecosystem survey area. On the other hand, in recent years an increasing number of large Greenland halibut has been captured in deeper waters of the area surveyed by the BESS (Fig 3.6.12). 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 3.6.13 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.

The fishable component of the population (length ≥45 cm) increased from 1992 to 2012, and has been stable since then (Fig 3.6.14). The harvest rate has been low and relatively stable since 1992.

Figure 3.6.12 Greenland halibut distribution (specimens/nautical mile) during August- September 2017 based on the BESS data.Figure 3.6.12 Greenland halibut distribution (specimens/nautical mile) during August- September 2017 based on the BESS data.

Figure 3.6.13. Biomass index for Greenland halibut at the nursery areas; 2014 excluded due to poor area coverage.Figure 3.6.13. Biomass index for Greenland halibut at the nursery areas; 2014 excluded due to poor area coverage.

Figure 3.6.14 Northeast Arctic Greenland halibut. Numbers (upper left) and biomass (upper right) 1992−2016 for 45+ cm Greenland halibut as estimated by the GADGET model, and estimated exploitation rates (below) (ICES 2017c).Figure 3.6.14 Northeast Arctic Greenland halibut. Numbers (upper left) and biomass (upper right) 1992−2016 for 45+ cm Greenland halibut as estimated by the GADGET model, and estimated exploitation rates (below) (ICES 2017c).

Deep-water redfish

Young of the year

In 2017, redfish, mostly Sebastes mentella, were distributed in western and northern areas of the Barents Sea, with the densest concentration west of Svalbard/Spitsbergen Archipelago. Estimated 0-group redfish biomass (100 thousand tonnes) was lower than the long-term mean (168 thousand tonnes). Abundance of 0-group redfish was lower than the long-term mean; thus, the 2017 year-class can be characterized as weak. However, some 0-group fish may occur outside of the area surveyed. The estimated index of 0-group redfish represents only shelf areas of the Barents Sea and, therefore, an unknown proportion of total 0-group abundance.

Older redfish

In 2017, deep-water redfish were widely distributed in the Barents Sea. During the ecosystem survey and the winter survey, the largest concentrations were observed, as usual, in the western and north-western parts of the Barents Sea. Biomass was at a higher level during 2013-2017 than in preceding years. Geographical distribution of deep-water redfish during the 2017 ecosystem survey is shown in Fig 3.6.15. Most adult fish are found in the Norwegian Sea. Stock development from the latest ICES AFWG assessment is shown in Fig 3.6.16.

Figure 3.6.15.  Geographical distribution of deep-water redfish during the 2017 BESS survey.Figure 3.6.15. Geographical distribution of deep-water redfish during the 2017 BESS survey.

Figure 3.6.16 Results from the statistical catch-at-age model showing the development of total biomass (‘000s), spawning stock biomass and recruitment at age 2 for the period 1992-2016, for <em>S. mentella</em> in subareas 1 and 2. (ICES 2017).Figure 3.6.16 Results from the statistical catch-at-age model showing the development of total biomass (‘000s), spawning stock biomass and recruitment at age 2 for the period 1992-2016, for S. mentella in subareas 1 and 2. (ICES 2017).