Most of the fish in the Barents Sea are demersal (Dolgov et al., 2011). The demersal fish community consists of about 70–90 regularly occurring species. These 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 based on data from the ecosystem survey in August- September can be found at: http://www.imr.no/tokt/okosystemtokt_i_barentshavet/ut- bredelseskart/en
Abundance estimates are available for the commercial species that are assessed. Figure 3.6.1 shows the biomass of cod, haddock and saithe (Pollachius virens) from the ICES AFWG assessments made in 2016. Saithe is mainly found along the Norwegian coast and off the coast south of the Barents Sea – little in the Barents Sea itself. The total biomass of these three species is close to the highest recorded (time-series start in 1960). Greenland halibut and redfish, in particular S. mentella, are important commercial species with a large part of their distribution within the BS: Time-series of biomass estimates of S. mentella and Greenland halibut are much shorter than those of haddock, cod and saithe. Apart from these main commercial stocks, long rough dab is the demersal stock with the highest biomass. Overall, cod is the dominant demersal species.
Young of the year
Cod were widely distributed in 2016, and the densest concentrations were found cod were found in the central, southern, eastern parts of the Barents Sea and northwest of Svalbard/Spitsbergen. The cod Archipelago were covered one month later than the main area and the southern Barents Sea was not completely covered. In 2016, the 0-group cod were also found in deeper water layer (100–200 m). The deeper layer was not regularly covered by trawl and only some catchers were taken to identify the acoustic registrations. Thus, the report present the standard coverage (0–60 m) only, and should be interpreted as minimum. The 0-group cod biomass (248 thousand tonnes) is 1.9 times higher than in 2015 (130 thousand tonnes) and 2.4 times lower than the long-term mean (603 thousand tonnes). The abundance index of 2016 year class is lower than long-term mean (Figure 3.6.2). The length of 0-group cod was between 2.9 and 13.5 cm. Most of the fish (69%) were between 7.5 and 9.5 cm, with a mean length of 8.9 cm, which is highest from 2007 and higher than the long-term mean of 7.6 cm.
The northeast Arctic cod stock is currently in a good shape, with high total stock size, and spawning-stock biomass (Figure 3.6.3). The 2004 and 2005 year classes were very strong, but after that recruitment-at-age 3 has returned to an average level (Figure 3.6.4). 0-group abundance has been very high in recent years (2011–2014), but this does so far not seem to result in strong year classes later on.
The strong 2004 and 2005 year classes have, together with a low fishing mortality, led to a rebuilding of the cod age structure to that seen in the late 1940s (Figure 3.6.5).
Young of the year
Haddock was relatively widely distributed in the western, central areas and north, west and east of Svalbard/Spitsbergen in 2016. The haddock biomass was 264 thousand tonnes and it is higher than in 2015 (178 thousand tonnes) and the long-term mean (164 thousand tonnes, for period 1993–2016). The number of fish belonging to the 0-group is lower than in 2015 and close to the long-term mean and thus can be characterized as average year class (Figure 3.6.6). The length of 0-group haddock varied between 3.0 and 16.9 cm, with mean length of 13.4 cm, and it is higher than long-term mean of 9.2 cm and is record high. The large 0-group haddock length may indicate suitable living conditions for young haddock in 2016.
The Northeast Arctic haddock stock reached record levels in 2009–2013, due to the very strong 2004–2006 year classes. After that, recruitment has normalized, and the stock has declined in recent years but is still at a high level (Figures 3.6.7 and 3.6.8).
Long rough dab
Young of the year
Long rough dab in 2016 were distributed mainly in the northern part of the Barents Sea. 0-group of long rough dab was observed both in pelagic and bottom catches indicating start of settlement to the bottom. Thus, the abundance indices were likely underestimated in 2016. The long rough dab index (526 million) in 2016 was the highest since 2009 and close to the long-term mean (Figure 3.6.9). Fish length varied between 1.0 and 5.0 cm with a mean length of 2.9 cm, and this is lower than the long-term average (3.3 cm).
Older long rough dab
Older long rough dab (age 1+) are widely distributed in the Barents Sea. During the Russian autumn-winter survey in October-December and ecosystem survey in August-September main concentrations of long rough dab were observed in the central-northern and eastern areas and were dominant by numbers in the bottom-trawl catches in surveys. Many small fish were observed in trawl catches especially in the eastern areas at the ecosystem survey in 2015–2016. In 2013–2015, long rough dab catch per unit of effort in Russian survey (Figure 3.6.10) and the biomass of long rough dab in the ecosystem survey in 2014–2016 (Figure 3.6.11) has been relatively stable.
Young of the year
Since 2005 only low concentrations of 0-group Greenland halibut were found. Greenland halibut were mostly observed around Svalbard/Spitsbergen, however in 2016, only north and south and southeast of Svalbard/Spitsbergen. The survey did not cover the numerous Svalbard/Spitsbergen fjords, where 0-group Greenland halibut are abundant, and therefore this index does not give the real recruitment (at age 0) to the stock, although it may reflect the minimum abundance index of the year-class strength in the standard long-term surveyed area. In 2012–2016 the abundance of Greenland halibut continuously decreased, and the 2016 year-class index is also low. Most of the fish (69%) were between 6.0 and 8.0 cm. The mean length of fish was 7.5 cm, which is at the same level as in 2015 and is the highest recorded.
Older Greenland halibut
The adult part of the stock was, as usual, mainly distributed outside the survey area. On the other hand, in recent years an increasing number of large Greenland halibut has been captured in the deeper waters in the surveyed area (Figure 3.6.12). The northern and northeastern areas of the sea serve as nursery area 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 area, based on the Ecosystem survey north of 76.5°N from northwest of Svalbard and east to Franz Josef Land.
The fishable population (length ≥45 cm) has increased from 1992 to 2012, and has been stable since then (Figure 3.6.14). The harvest rate has been relatively stable since 1992.
Figure 3.6.14 Northeast Arctic Greenland halibut. Numbers (upper left) and biomass (upper right) 1992−2014 for 45+ cm Greenland halibut as estimated by the GADGET model, and estimated exploitation rates (be-low) (ICES 2016c).
Young of the year
Redfish, mostly Sebastes mentella, are distributed in the western part of the Barents Sea and north of Svalbard/Spitsbergen. The 0-group redfish biomass in 2016 (58 thousand tonnes) was lower than in 2015 (231 thousand tonnes) and 3 times lower than the long-term mean. The abundance of 0-group redfish is 7.9 times lower than in 2015 and 4.6 times lower than the long-term mean. Thus the 2016 year class can be characterized as weak. The index of 0-group redfish in the Barents Sea is an unknown proportion of the total 0-group abundance, and therefore representative only for the shelf area of the Barents Sea.
Deep-water redfish were widely distributed in the Barents Sea. At the ecosystem survey and the winter survey, the main concentrations of deep-water redfish were found, as usual, in the western and northwestern parts of the Barents Sea. The biomass of deep-water redfish in the Barents Sea has been at a higher level in 2013-2016 than in the preceding years. The geographical distribution of deep-water redfish during the ecosystem survey in 2016 is shown in Figure 3.6.15. Most of the adult fish is found in the Norwegian Sea. The stock development of redfish from the latest ICES AFWG assessment is shown in Figure 3.6.16.
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 1992–2015, for S. mentella in Subareas 1 and 2. (ICES 2016c)