Joint Russian Norwegian Arctic Fisheries Working Group (JRN-AFWG) Report 2025

The aim of this chapter is to identify important ecosystem information influencing the fish stocks. Ecosystem and climate changes, along with fishery, determine the stock dynamics of commercial species. Water temperature and ice conditions influence the distribution of the commercial fishes in the Barents Sea. Apart from this, temperature also impacts growth rate and mortality at the early stages (larvae, juveniles). Currents affect the strength of year-classes by providing transport of eggs, larvae and 0-group of commercial species from the spawning areas into the Barents Sea. Food availability is another important ecosystem driver that influence the rate of growth and maturation of commercial fishes. It depends not only on the prey availability, but also on feeding competition. Mortality due to predation, including cannibalism, can greatly affect population abundance of commercial species. The impact of ecosystem changes on the dynamics of bycatches of juveniles and non-target species in mixed fisheries should also be taken into account.

The Barents Sea ecosystem survey (BESS):

The aim of the Barents Sea ecosystem survey (BESS) in August-October is to monitor the status and changes in the Barents Sea ecosystem. In 2018, and 2022, BESS coverage was incomplete, and in 2020 it was delayed, making the evaluation of the ecosystem status more uncertain. The 2024 BESS was carried out during the period from 17-th August 2024 to 12th October by three Norwegian and one Russian research vessels. The temporal and spatial progression during the survey was good, despite technical problems and bad weather (Figure 1.1a and b).

Current state and changes

Abiotic conditions

Sea Surface Temperature (SST) in both the southern and northern Barents Sea were at, or slightly below, the long-term mean (1991-2020) for the first half of 2024. However, the SSTs rapidly increased in late June/early July reaching 3-3.5^oC above the seasonal mean in August-September. These conditions were associated with a marine heatwave. The sea surface stayed warmer than the long-term mean for the rest of 2024 and at least to the end of February 2025. Despite a strong marine heat wave at the surface, it did not reach deeper waters at the time. Observations from the full water column in August-October reveal that the heat wave was present only in the upper 30 m of the water column. Below, most of the ocean had temperatures 0-1^o C above the long-term mean. The exception was some patches with higher anomalies around Svalbard.

The southwestern Barents Sea is strongly affected by the varying characteristics of the inflowing Atlantic Water (AW). The long-term time series from standard sections reveal an increasing temperature trend in the Atlantic Water since the late 1970s. Temperatures in the inflowing water decreased from 2015-2019/2021 . The last 4-5 years the temperatures in summer have increased, but the winter temperatures do not show the same pattern (Figure 1.2).

Sea ice conditions in the northern Barents Sea in early winter 2024 were highly fluctuating with more sea ice than the long-term mean for about two weeks in January followed by small amounts of sea ice in February and then increasing SIA to levels above the long-term mean during late March to April. SIA was close to normal during May and the first half of June, and well below the long-term mean for the rest of 2024 and in January-February 2025.

The area of the Barents Sea occupied by bottom waters with a temperature < 0°C amounted to 31%, which was substantially higher compared to 2023 and somewhat below the level of 2019-2022 (Fig. 1.3). According to the expert evaluation, Atlantic water temperature in the Murman Current in 2025 is expected to remain typical of warm years. Due to high temperatures and low sea-ice extent in recent years, the ice coverage of the Barents Sea is expected to remain below normal. Lower-than-average ice coverage and longer duration of ice-free season increase the primary productivity of the Barents Sea.

There is no trend in the volume transport across the Barents Sea Opening when investigating the full time series. However, there appear to be shifts between periods. The period 1997-2006 had highly varying volume transports. The period 2007-2020, on the other hand, was more stable, with the exception of the extreme years of 2015-2016. From 2021 and onwards, the volume transport has been rather weak compared to before, in particular in spring/early summer and fall.

Mesozooplankton

The total mesozooplankton biomass in autumn 2024 was similar to preceding years in most of the Barents Sea. However, in several subareas of the Norwegian sector, where size-fractioned biomass data are available, the biomass of the mid-size fraction (typically representing older stages of large copepods like Calanus spp.) has been very low since 2020. During the same period, the biomass of the smallest size-fraction (typically representing young stages of intermediately sized copepods, as well as smaller species) has displayed a strong increase.

The changes in the biomasses of the intermediate and small zooplankton size-fractions may reflect a combination of factors including the predation pressure from the large fish stocks, possibly a lower advection of mesozooplankton with inflowing waters into the BS in recent years, as well as variability in local production rates.

Krill indices of biomass have shown increasing trends over recent decades to the increased contribution from M. norvegica in the BS.

Prey stocks

Euphausiids, amphipods and shrimp are important prey for most commercial fish in the Barents Sea. In 2023 the total biomass of euphausiids was slightly less than long term mean (1980-2023). In recent years, the northern shrimp stock has remained stable, showing fluctuations but without a clear trend. Indices were not updated in 2024.

Capelin, polar cod and young herring are the main forage pelagic fish in the Barents Sea, which are important prey for most predators in the area, including commercial demersal species. These species are very sensitive to various changes in the ecosystem, the influence of predators, fishing, or the plankton . Total biomass of the main pelagic species during 1986–2024 has fluctuated between ca. 0.5 and 9 million tonnes; largely driven by fluctuations in the capelin stock (Figure 1.4). During 2020-2024 (except for the year 2022 with poor survey coverage), the combined biomass of capelin, herring, polar cod, and blue whiting has been above the long-term average after a low-biomass period from 2014-2019. The biomass during this latter period has been dominated first by capelin from the 2019 and 2020 year-classes, and in the last two years by herring from the 2021 and 2022 year-classes.

The recent strong recruitment to the polar cod stock in 2016 and 2020 led to sudden increases in stock size, but the stock sizes decreased again rapidly (Figure 1.4). Polar cod are predicted to experience decrease in habitat and abundance with a warmer and more ice-free Barents Sea, and t here is also a high probability that polar cod are now distributed outside the standard survey area in the Barents Sea.

Specification of the ecosystem impact on the assessed species:

Cod

The cod stock has been decreasing, but predictions indicate that it will stabilize on a low level. The main effect of the ecosystem impact on cod stock dynamics is manifested in the change in the abundance of its recruitment. There have not been any strong year-classes of cod since 2005 despite high cod SSB and above average sea temperatures. Recruitment has previously been shown to be positively correlated with both those factors, but in recent years this is no longer the case. Meso-zooplankton is important for survival of larvae and 0-group cod, so their distribution must overlap with areas of relatively high plankton biomasses. Despite a large number of studies (see e.g. summary in Ottersen et al., 2014), the underlying mechanism of the impact of the Barents Sea ecosystem on cod recruitment is still not well understood.

Cod diet

Cod is a main predator among fishes in the Barents Sea. Its diet was relatively stable in recent years; capelin was the main prey. The diet composition of cod in 2024 was rather similar to that in 2023 (Figure 1.5). Since 2013 the importance of snow crab in cod diet considerably increased and has since then consisted of 3-7 % by weight (Figure 1.6). It should be noted that in 2022-2023 an unexpected increase of red king crab, up to 3-5 % by weight in the diet was observed (Figure 1.6), but cod consume only crab legs, empty carapaxes after molting or individuals with soft carapax immediately after molting. Figure 1.7 shows the consumption by cod in the period 1984-2024. Consumption of most prey has decreased in recent years due to decreasing cod abundance. Total prey consumption in 2024 was very close to that in 2023.

Figure 1.8 and 1.9 show the proportion of cod and haddock in the diet of cod. Predation of cod on juvenile cod and haddock was relatively low in 2020-2023, but the proportion of haddock in cod diet increased considerably from 2023 to 2024, which is consistent with the increased abundance of young haddock in recent years. The proportion of cod in cod diet also increased somewhat from 2023 to 2024.

Individual growth of cod now seems to have stabilized. Feeding conditions for cod are expected to be adequate in the near future, as the cod likely will be able to feed on other prey despite the present low capelin stock level (see Gjøsæter et al. 2009 for a discussion of ecosystem effects of capelin collapses). Also, the cod stock is low so there will be less competition for food.

Haddock

Warm conditions are necessary, but not sufficient conditions to ensure good recruitment and growth. Plankton bloom (timing and strength) and influx are important for year-class formation. The year classes 2018-2020 were poor, but the reasons are not fully explored. The year-classes 2021-2024 appear to be average, or above average. There is no clear recent trend in the condition factor of haddock (Figure 1.10). Older haddock includes a high proportion of benthic invertebrates in their diet, but the availability of this prey group is not known. The low cod stock should lead to less predation on haddock by cod, and therefore lower mortality on both pre-recruits and younger haddock recruited into the fishery.

Haddock diet

The diet composition of haddock is presented in Figure 1.11. Haddock is a benthivorous species and feeds mainly on polychaets, echinoderms and molluscs (on average up to 43 % by weight). However, euphausiids and fish (including capelin and herring) can be important prey items (on average up to 13 % and 17 % by weight respectively).

Greenland halibut

The distribution of the Northeast Arctic Greenland halibut stock is very uneven in the Barents Sea and adjacent waters and strongly depends on the migrations that it makes throughout its life. The highest densities of adult fish are observed in spawning grounds on the slope of the continental shelf. Juveniles are widely distributed along the northern part of the shelf and the northern part of the Barents Sea. Their abundance in the Barents Sea may be affected by water temperature and currents, although the effect of these factors is not fully understood and uncertain. Growth and maturation of the Greenland halibut depend on prey abundance. Greenland halibut feeds on zooplankton, shrimp, capelin, herring, polar cod and other small fishes. Cod can be both predator and food competitor for Greenland halibut, but spatial overlap is observed mainly between cod and Greenland halibut juveniles. Cannibalism can also be observed in areas with the overlapping of adults and juveniles. Mammals can consume Greenland halibut in the spawning areas.

The Greenland halibut stock has experienced notable changes over the past two decades. In the early 2000s, the stock was considered relatively stable, supported by moderate fishing pressure. From 2009, fishing activity has increased significantly, which has contributed to a gradual decline in both harvestable biomass and spawning stock biomass (SSB). By 2024, stock indicators suggested increased pressure on the population, as the SSB had fallen below precautionary reference points and the harvest rate exceeded sustainable levels. These developments highlight the importance of continued monitoring and adaptive management to support the long-term sustainability of the stock.

Beaked redfish

As a boreal species, it is benefiting from the warming in the Barents Sea. Its stock has increased in recent years, but stock assessment of this species is characterized by high uncertainty. Feeding condition for beaked redfish, which feeds on zooplankton and small fish (capelin), in 2022-2023 were likely to be relatively stable. Cod and Greenland halibut are main predators for the beaked redfish. However, as abundance of these species is declining and abundance of capelin, herring and polar cod is increased, the predation pressure on redfish is probably relatively low. In recent years, the total number of redfish juveniles, mostly S. mentella , caught as bycatch in the international shrimp fishery has increased (see text and figure below). This strongly depends on the overlap between the distribution areas of redfish juveniles and shrimp fishery areas. The stock size and distribution of shrimp as well as currents and temperature affect this.

Marine mammals

In the Barents Sea, about 15 cetacean species, 7 seal species and the polar bear can potentially be observed. The white-beaked dolphin is the most common cetacean species to be seen within the Barents Sea as it is distributed all over the area. Among the large baleen whales, especially minke whales, but also fin whales, are distributed over large parts of the Barents Sea, and are seasonally present at relatively high numbers. Humpback whales have much more aggregated distributions north and west of Hopen and around Bear Island, and these locations are also shared by the other baleen whale species.

In 2024, white-beaked dolphins were the most frequently observed, although lower in numbers than in previous years. Dominant species in the group of baleen whales were humpback whales and fin whales. Aggregations of humpback whales in areas East of Svalbard commonly overlap with capelin distribution.

Food web and species interactions

The Barents Sea food web is a relatively well-studied, cold-water marine ecosystem characterized by strong seasonal productivity and top-down control by predators (Blanchard et al. 2002, Wassmann and Reigstad 2011 ) . At its base, the food web starts with phytoplankton, which bloom in spring and are grazed by zooplankton such as Calanus finmarchicus . These in turn support a variety of pelagic fish like capelin ( Mallotus villosus ), herring, polar cod and the early life-stages of demersal fish. Demersal fish (e.g., cod, Gadus morhua ) feed on both pelagic and benthic prey, while marine mammals (such as harp seals and whales) and seabirds (e.g., auks) act as apex predators. The web is influenced by climate-driven changes in ice cover and inflow of Atlantic waters, affecting species composition and productivity.

A model for assessing the food web of marine mammals and fish in Barents Seas developed by Planque et al. (2024) is shown in Figure 1.12. Marine mammals consume large quantities of food, comprised of fish, including cod and lower trophic level species that support commercial fish stocks.

According to Mauritzen et al. (2022) marine mammals consume about 535 000 tons of gadoid species annually in the Barents Sea. We should get more information about the gadoid species composition and size of this prey in their diet to better evaluate the mortality caused by marine mammals compared to cannibalism, fishing mortality and other natural mortalities. For Northeast Arctic cod, total cannibalism during the record high spawning stock biomasses (SSB) during 2011-2015 was up to 370 000 tons (2013), while cannibalism in 2024 was estimated to 112 000 tons (Table 1.1).

Concerns have been raised, and questions asked why the number of Northeast Arctic cod surviving to age 3 did not increase despite the record high SSBs producing these year-classes in 2011-2015, and the evidence of strong new year-classes being produced at the 0-group stage (Figure 1. 13a-c ). Possible explanations for the low survival to age 3 are fishing (e.g., bycatch of juveniles in shrimp fishery), climate, food, predation, cannibalism and random effects. All these explanations should be further investigated to see if one in the future could gain more long-lasting effects of keeping high SSBs although cannibalism and predations by marine mammals are likely the main reasons.

A:                                                                    B:                                                                     C:

Discards and young fish bycatch in mixed fishery

In this report, the terms ‘landings’ and ‘catches’ are, somewhat incorrectly, used as synonyms, as discards are in no cases used in the assessments. This does not mean, however, that discards have not occurred, but the WG has no information on the likely extent. Available information indicates low discard rates at present (less than 5% of catch), and it therefore is assumed that discards are negligible in the context of the precision of the advice.

We would note that there have been historical periods with significant mis-reporting, and for further information on under- and misreporting, we refer to the 2016 and 2022 AFWG reports.

Bycatch estimates (1994–2024) of redfish, cod, haddock, Greenland halibut and polar cod juveniles in the commercial shrimp fishery in the Barents Sea are presented in Figure 1. 14 . These estimates are obtained with a spatio-temporal model based on a procedure elaborated in Breivik et al. (2017). In Breivik et al. (2017) an extensive validation study indicates that the procedure obtains bycatch estimates with approximately correct uncertainty. The bycatch estimates illustrated in Figure 1. 14 are available for each quarter in each main statistical area (not shown in report). Note the increase in bycatch of redfish juveniles in recent years. In the Barents Sea , genetic analyses of redfish juveniles collected from bycatches in the shrimp fishery some years ago showed that 97% of the redfish juveniles were S. mentella (K. Nedreaas, pers.com .). Most of the redfish bycatch are 8-15 cm and 1-3 years old S. mentella with an average weight of about 22 g. A bycatch of 30 million redfish hence corresponds to 650 tons bycatch compared to 33 000 tons eaten by cod in 2024. On the other hand, 10 million 2-year-old redfish bycatch (i.e., 1/3 of the total bycatch) is about 4% of the assessed total stock number of 2 year olds (Howell et al. 2024). The current stock assessment of S. mentella is less accurate with regards to small fish since it mainly focuses on the fished part of the stock. The natural mortality of the smallest redfish caught as bycatch is also likely higher than M=0.05 used in the current stock assessment.

The time-series in Figure 1.14 are obtained by scaling the estimated bycatch in the Norwegian shrimp fishery with the international fishery in e.g., each season and ICES area. The scaling procedure assumes that the Norwegian fishery is representative of the international shrimp fishery with regards to bycatch. This assumption is necessary because the international catch data are available only to a low spatio-temporal resolution. If the international vessels to a relatively high degree trawl at locations not trawled by Norwegian vessels, the bycatch estimates illustrated in Figure 1. 14 may be biased. The estimated bycatches do not include larger fish kept in escapement bags in some countries’ shrimp fisheries in international waters (the “Loop-hole”).

The same spatio-temporal model may also be used as a tool to open closed areas.

Sampling of commercial catches – age and length sampling

Tables 1.2–1.5 show the development of the Norwegian, Russian, Spanish and German sampling of commercial catches in the period 2008–2024. The tables show the total sampling effort, but do not show how well the sampling covers the fishery. Indices of coverage should be developed to indicate this. The main reason for the general strong decrease in numbers of Norwegian samples in the first part of this period is the termination of the port sampling program in northern Norway. This program is now up and running again. It should be considered whether catch sampling carried out by different countries fishing by trawl for the same time and area could be coordinated and data shared on a detailed level to a greater extent than is done today. It is also possible for Norway to provide stock coordinators in other countries with samples collected by the Norwegian Coastguard during their inspections of foreign vessels.

**In addition to age the otoliths are also used for identification of coastal cod.

**Age samples from surveys with commercial trawl come in addition.

***From 2013 No. of unique vessels are split by length and age samples.

****Only from large, meshed gillnets as basis for assessment.