Scientific report from the Norwegian and Russian Barents Sea Ecosystems Survey in August-October 2025 (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. The survey has been conducted annually since 2004, as collaboration between the IMR in Norway and the Polar Branch of VNIRO (PINRO) in Russia. The general survey plan, tasks, and sailing routes are usually agreed upon at the annual PINRO-IMR Scientists’ Meeting in March. From 2024, the meeting has gone digital due to external factors. The 22nd BESS was carried out during the period from 22nd August to 15th October 2025 by the Norwegian research vessels (“Helmer Hanssen”, “G.O. Sars” and “Johan Hjort”) and the Russian vessel (“Vilnyus”). The scientists and technicians taking part in the survey onboard the research vessels are listed in Table 1. As always, we would like to express our sincere gratitude to all the crew and scientific personnel onboard the research vessels for their dedicated work. We would also express our sincere gratitude to all the people involved in planning and reporting of BESS 2025.The purpose of this survey report is to summarize the status of the environmet and the living organisms of the Barents Sea based on the survey data. The information obtained in BESS 2025 will be further used for the assessment of fish and invertebrate stocks, the evaluation of changes in environmental conditions and biota, and the implementation ov various international and national projects. 

Figures by: Stine Karlson

BESS aims at covering the entire, ice-free area of the Barents Sea, progressing from south to north. Ecosystem stations are distributed in a 35×35 nautical mile regular grid, and the ship tracks follow this design. Exceptions are the areas west and north of Svalbard/Spitsbergen, where the tracks follow a zig-zag design where depth stratified (100-300m and 300-500 m) bottom trawl hauls for demersal fish survey indices estimation are distributed along the tracks. There are also additional acoustic transects between the tracks covering the ecosystem stations east of Svalbard/Spitsbergen, and south of Franz Joseph Land, to increase the overage for acoustic capelin stock size estimation. This constitutes a standard plan for the survey.

The planned vessel tracks for BESS 2025 are given in Fig. 2.1. The plan for the Norwegian vessels had to be changed relative to the standard plan due to issues with the time allocation between Norwegian vessels. Due to this, we had to plan for a later coverage by “G.O. Sars” part 2 of the areas between Bear Island and Svalbard/Spitsbergen, as well as a central part of the Norwegian Exclusive Economic Zone (NEEZ). BESS 2025 was largely implemented according to this modified plan.

The Russian RV “Vilnyus” covered the eastern and north-eastern parts of the Barents Sea within the Russian Exclusive Economic Zone (REEZ), as well as bottom trawls in the Russian shelf part of the Loophole. Norwegian RVs covered the western part of the Barents Sea and an area around Svalbard/Spitsbergen within the NEEZ, as well as pelagic samples in the Russian shelf part of the Loophole. More specific, “Johan Hjort” covered the western part of the NEEZ south of Bear Island, as well as the areas west of Svalbard/Spitsbergen in NEEZ, which is part of the capelin feeding area. “G.O. Sars” covered the eastern part of NEEZ, and the central parts according to the modified plan. “Helmer Hanssen” covered the areas west, north, and north-east of Svalbard/Spitsbergen. The realized research vessel tracks with sampling for the BESS 2025 are shown in Figs. 2.2 and 2.3. Exceptions to the planned coverage were one missed station in the central NEEZ due to time constraints, and a larger area west of Novaya Zemlya in REEZ where only acoustic transects were carried out, because trawls operations are prohibited in this area.

The planned time schedule for BESS 2025 was 155 days (100 NOR+55 RUS), while the effective vessel days (time between first and last sample in the vessel logs) was 141 days (89 NOR+52 RUS). The difference between the two is as expected, as vessels need time for sailing to and from harbours, some preparation before sampling at stations, and due to incidents of bad weather. The overall temporal and spatial progression during the survey was according to the ideal southwest to northeast progression (Fig. 2.4). An exception due to the later coverage by “G.O. Sars” part 2 of the areas between Bear Island and Svalbard/Spitsbergen, as well as a central part of the NEEZ is visible.
 

2.1  Sampling methods

The ecosystem survey in 2025 was like previous years, covering most ecosystem components. In addition, the standard oceanographic sections "Vardø-Nord" and "Hinlopen" were taken by the Norwegian vessels, and the “Kola” (twice) and Kanin sections were taken by the Russian vessel (Fig. 2.3). Summarizing the standard sampling gears at the BESS 2025; in total 311 pelagic hauls, 354 demersal hauls, 432 CDT, and 430 plankton nets were taken.

In 2025, compared to 2024, there were no changes in sampling gear. Manta trawl was included as standard equipment for monitoring microplastics at BESS in 2022 and was also used in 2025. 50 Manta samples were collected on the Russian vessel, and 38 on board the Norwegian vessels. In addition, 34 fish stomachs were sampled on the Russian vessel for the same purpose.

A new length stratified individual sampling of haddock was introduced in 2022, increasing samples from one to two fish taken per 5 cm group. This continued in 2025. 
Plankton stations were carried out throughout the entire area covered by the survey with sampling from surface to bottom. On the Kola hydrological section, plankton samples are collected separately for the layers: 0-50 m, 0-100 m and 0 to bottom.

The survey sampling manuals can be obtained by contacting the survey coordinators. These manuals include methodological and technical descriptions of equipment, the trawling and capture procedures by the sampling tools, sampling and registration of the ctach in the lab, and the methods thatbare used for calculating the abundance and biomass of biota.

2.2 Special investigations

BESS is a useful platform for conducting additional studies in the Barents Sea. These studies can be testing of new methodology, sampling of data additional to the standard monitoring, or sampling of other types of data. It is imperative that the special investigations do not influence the   standard monitoring activities in the survey. The special investigations vary from year to year and below is a list of special investigation conducted on Russian and Norwegian vessels at BESS 2025, with contact persons. This chapter also briefly mentions some investigations that are typical during survey but not described in the main text of the BESS Report.

2.2.1 Annual monitoring of pollution levels

In 2025 PINRO continued the annual monitoring of pollution levels in the Barents Sea in accordance with a national program. Samples of seawater, sediments, fish and invertebrates were collected and analyzed for persistent organic pollutants (POPs, e.g. PCBs, DDTs, HCHs, HCB) and heavy metals (e.g. Pb, Cd, Hd) and As. The samples were collected at RV "Vilnyus" during BESS in different parts of the Barents Sea. The results from chemical analyses are available in the annual PINRO report “Status of biological resources…”. 

Contact: Andrey Zhilin, PINRO (zhilin@pinro.vniro.ru)

 2.2.2 Collection of samples for biochemical studies

Frozen samples of commercial and non-commercial fish and invertebrates were collected for biochemical studies (ratio of body parts, chemical composition of nutrients, molecular weight of muscle proteins, amino acids and lipid fractions composition) in accordance with a research program. Samples were frozen at temperature -18°C immediately after catching before rigor mortis.

Contact: Kira Rysakova, PINRO (rysakova@pinro.vniro.ru)

 2.2.3 Fish pathology and parasitological research

PINRO undertakes yearly investigations of fish diseases in the Barents Sea (mainly in REEZ). Seven commercially important fish species were analyzed visually (19321 individuals) and 957 individuals for detailed parasitological analysis. In addition, red king crab and snow crab (in total 526 individuals) were examined for “shell disease of crustaceans”. The main purpose of the pathology research is annual estimation of epizootic state of commercial fish and crab species. The observations are entered into a database on pathology. This investigation was started by PINRO in 1999. Results are available in the annual PINRO report “Status of biological resources…”

Contact: Irina Mukhina, PINRO (imukhina@pinro.vniro.ru)

2.2.4 Hydrochemical observations

In August and October, hydrochemical observations were made onboard RV “Vilnyus” in the Kola section. Dissolved oxygen in the surface and bottom layers as well as biochemical oxygen demand during 5 days in the bottom layer were measured.

Contact: Mikhail Antsiferov, PINRO (mikmikru@pinro.vniro.ru)

2.2.5 Fish diet study

Since 2004, investigations of diet of most abundant pelagic and demersal fish have been conducted annually during the BESS. Stomach samples from polar cod and capelin, and cod, are collected as standard at both Russian and Norwegian vessels, and the detailed sampling is reported in the chapters about pelagic and demersal fish, respectively.

The Russian vessel in 2025 also collected stomachs from Atlantic herring, haddock, Greenland halibut and skates (704 individuals), and snow crab (96 individuals) were fixed for detailed analysis. In addition, 4026 stomachs of 16 fish species were sampled and analyzed by “express quantitative analysis”.

Contact: Andrey Dolgov, PINRO (dolgov@pinro.vniro.ru), Irina Prokopchuk, PINRO (irene_pr@pinro.vniro.ru), Bjarte Bogstad, IMR (bjarte.bogstad@hi.no)

2.2.6 Water samples for eDNA analyses

In 2016 we collected eDNA (environmental DNA) samples in the North of Svalbard and the Barents Sea to test if the method can map the distribution of fish species in an easier way compared to traditional methods as conventional trawling. The eDNA is sequenced and species are identified by comparing these sequences (Barcode) against a reference database. Since 2018, we have sampled and analyzed the DNA. In the NFR project FISHDIV we have developed a method to quantify biomass of fish species (including Atlantic cod and herring) in fjords. Next step would be to test this method for fish species in the Barents Sea. The analysis of eDNA can identify all species such as marine mammals, fish and zooplankton in a drop of water. The analysis of eDNA through metabarcoding (massive parallel DNA sequencing) is an established and validated method for species identification/community analysis but has not been used routinely on expeditions in the Barents Sea. This type of DNA sample can support other sampling to monitor species composition in the Barents Sea. It is a method for the future and would be important in assisting in monitoring species distribution in relation to climate change.

Contact: Torild Johansen, IMR (torild.johansen@hi.no)

2.2.7 Water samples for radioactivity

Sampling of seawater from a total of 6 CTD stations, 125 l seawater taken from the sea water tap on deck. The water samples will be used for analyses and monitoring of radioactivity in seawater in the Barents Sea.

Contact: Hilde Elise Heldal, IMR (hilde.elise.heldal@hi.no)

2.2.8 Microplankton metabarcoding samples

Microplankton metabarcoding samples are collected from 10 m CTD water at standard stations where time allows. Samples collected through this special investigation will be used to test a new methodology to characterize microplankton community composition, DNA metabarcoding. Metabarcoding samples will be collected on the G.O. Sars at all standard stations when possible, completing a three-year time series in the region. The standard method used to characterize microplankton communities, microscopy, is relatively expensive and can only resolve visually distinct taxa. DNA metabarcoding will complement microscopy by increasing the spatial and taxonomic resolution of our results regarding microplankton community distribution and composition. The results from this investigation can be used to inform decisions regarding the value and role of metabarcoding in Barents Sea ecosystem monitoring efforts. This work is a continuation of phytoplankton metabarcoding sampling conducted in 2022-204 and includes the collection of similar samples for 2025.

Contact: Sarah Lerch, IMR (sarah.lerch@hi.no)

2.2.9 Additional WP2 samples at 100-0m

WP2 net lowered to 100m depth and then pulled vertically up to the surface. If sufficient time is available, 100–0 m samples are desired at all plankton stations.

We apply for zooplankton sampling with WP2 net for the upper part of the water column (100-0m), which comes in addition to the sampling already established for the bottom-0m stratum. This “double sampling” is already performed along the transects, but we now wish to extend this to all plankton stations. This double sampling was standard procedure from about 1990-2014, but the sampling was thereafter limited to the bottom-0m stratum. The reason for asking to re-establish the 100-0m sampling is that this better represents the depth-habitat for young stages of fish, thereby probably being more relevant as a proxy for their ambient feeding environment than the bottom-0m stratum. That said, the bottom-0m samples are vital when assessing trends and year-to-year variation in plankton abundance as these represent the whole plankton community in the entire water column. I believe the 100-0m samples might become an additional valuable ecosystem indicator when assessing the underlying reasons for the variation in years class strengths and poor recruitment of the fish stocks in the later years. Hence, both types of samples are important, but in different ways.

Contact: Espen Bagøien, IMR(espen.bagoien@hi.no)

2.2.10 Freeze samples of krill, amphipods, and capelin for nutrient analysis

Capelin and krill are important prey for baleen whales in the Barents Sea. In order to investigate how baleen whales assimilate nutrients during digestion, samples of capelin and krill will be analyzed for macronutrients and trace metals and later compared with nutrient contents in whale excretions. For this reason, samples of capelin and krill were taken at several relevant stations during the ecosystem cruise. In each station, a sample of 25 capelin and 50 krill were collected and stored in the freezer. This work is part of the EU project OceanICU.

Contact: Carla F. Brandt, IMR (carla.freitas.brandt@hi.no) and Martin Wiech (Martin.Wiech@hi.no)

2.2.11 Sub-samples from WP2 and MultiNet Mammoth nets for molecular analysis of zooplankton

Quantitative sub-samples will be taken from all standard zooplankton samples from WP2 and MultiNet Mammoth nets) for molecular analysis (community DNA metabarcoding). These samples (1/4 of the total sample) will be homogenized onboard and a portion of the homogenate will be preserved in TES buffer. This procedure saves significant downstream processing time in the lab and avoids the use of ethanol which presents many logistical challenges. These samples will complement traditional microscopic sorting by generating high-resolution species-level data on the zooplankton communities and allowing to process more samples than would be possible through microscopic analysis alone. This will also generate data on groups often missed by microscopy, such as cryptic species and larvae of benthic animals, including commercially and ecologically important ones, such as king- and snow crab.

Contact: Espen Bagøien, IMR(espen.bagoien@hi.no)

2.2.12 Freeze samples of zooplankton analysis of vitamin B and lipids

Zooplankton collected from WP2-net or from demersal trawl samples are frozen at selected stations. The samples from WP2-net are fractionated using the standard method (180-1000 µm, 1000-2000 µm, for >2000 µm). When possible, we do also wish for species sorted samples (see table 1). The frozen material will be brought back to the lab in Bergen for further analysis of b-vitamin, fatty acids and stable isotope analysis.

Contact: Kaja Skjærven, IMR (Kaja.Skjaerven@hi.no) and Sonnich Meier, IMR (sonnich@hi.no)

2.2.13 Freeze samples of 0-group capelin, herring and redfish

Small juvenile 0-group herring, capelin and redfish from pelagic and demersal trawl samples are frozen at selected stations. The frozen material will be brought back to the lab in Bergen for further analysis of condition/growth, fatty acids and stable isotope analysis.

Contact: Sonnich Meier, IMR (sonnich@hi.no)

2.2.14 Freeze samples of juvenile cod and polar cod

Small juvenile cod and polar cod, mainly 0-group and some 1-group from pelagic and demersal trawl samples are frozen at selected stations. Otoliths of sampled cod will be used for two MSc projects at UiB and IMR dealing with 3 D otolith structure and relative otolith versus somatic growth. The frozen material will be brought back to the lab in Bergen for further analyses of condition and growth within the framework of an RCN-proposed project. These analyses are dependent on higher resolution of fish attributes than normally possible at sea.

Contact: Arild Folkvord, IMR/University of Bergen (Arild.Folkvord@uib.no)

2.2.15 Freeze samples of deep-water shrimp

A total sample of 3 kg of whole shrimp from the Barents Sea, collected anywhere in the Barents Sea, are frozen and brought on land. The sample will be used for analyses and monitoring of radioactivity in shrimp in the Barents Sea.

Contact: Hilde Elise Heldal, IMR (hilde.elise.heldal@hi.no)

2.2.16 Freeze sample of Iceland scallop

There is a mismatch between the generally assumed distribution of the commercially important Iceland scallop (Chlamys islandica) in the Barents Sea and Svalbard area and much more widely registered observations on the BESS. Using genetic analysis to confirm species identification and study the population structure will help to improve our understanding of the distribution of this species and links to bathymetry, habitat and environment. Up to 30 individuals per station will be collected and stored at -20C for tissue sampling, morphological analysis and ageing. The results will contribute to the stock assessment and fisheries advice for Iceland scallops in the Barents Sea and Svalbard/Spitsbergen area.

Contact: Fabian Zimmermann, IMR (fabian.zimmermann@hi.no)

2.2.17 Acoustic target strength (TS) measurements of capelin

Fish target strength (TS) is a key parameter for abundance and biomass estimation of fish stocks when using the acoustic echo integration methods. A 5-days period on RV Johan Hjort was dedicated to obtaining acoustic data suitable for target strength measurements with a TS probe. This is a platform equipped with five echosounders (38 kHz narrowband and 70, 120, 200, and 333 kHz broadband) and transceiver tubes that can be lowered close to the targets. There were problems with the main plug between the probe and the winch cable were solved by opening the probe and using spare connectors. Unsuccessful calibration of probe echo sounders because it was impossible to obtain isolated sphere targets due to abundant fish around the sphere in the calibration site. TS probe will require permanent repair of defects and complete maintenance of all systems (including relay module and pitch/roll motors). During the survey, fish aggregations that were evaluated as capelin using the echo sounder data, were confirmed to be polar cod after trawling. Contrary, aggregations that were not considered to be capelin because of high backscattering in high frequencies, corresponded to capelin after trawling during the acoustic coverage in the capelin area after the 5-days test. The anomalous frequency response observed coincide with what was measured during surveys in the spawning period in the coast of Finnmark in February-March.

Contact: Georg Skaret, IMR (georg.skaret@hi.no) and Hector Pena (hector.pena@hi.no)

3.1 Data Bases

A wide variety of data are collected during the ecosystem surveys. All data collected during the BESS are quality controlled and verified by experts: oceanography by Randi B. Ingvaldsen (IMR) and Aleksandr Trofimov (PINRO) fish catch data by Herdis Langøy Mørk (IMR) and Tatyana Prokhorova (PINRO) during and after the survey; plankton data by Jon Rønning and Espen Bagøien (IMR) and Irina Prokopchuk (PINRO); benthos data by Anne Kari Sveistrup (IMR) and Nataliya Strelkova (PINRO); and marine mammals data by Frederike Boehm (IMR) and Roman Klepikovskiy (PINRO). The data are stored in IMR and PINRO national databases, with different formats. However, the data is exchanged so that researchers in both institutes have access to each other’s data and use equal joint data.

3.2 Data Application and reporting

The BESS aims to cover the whole Barents Sea ecosystem geographically and provide survey data for commercial fish and shellfish stock assessment. Data for stock assessment of capelin is particularly important, because capelin TAC (Total Allowable Catch quota) is specifically based on the results from this survey. The Norwegian-Russian Fishery Commission determines TAC immediately after the survey. In addition, a broad spectrum of physical variables, ecosystem components and pollution are monitored and reported, and included in other kinds of assessments, e.g. ecosystem-based assessments. The survey data will be used by each party for various purposes within the framework of national and international programs.

This survey report is based on joint data and contains the main results of the monitoring. The survey report will be published  in the report series «IMR/Polar Branch of VINRO Joint Report Series. 

Prior to this report, the survey reports from BESS in the period 2004 – 2025 have been published in the report series “IMR/PINRO Joint Report series”.

All reports from BESS from 2004 until the latest are available at this web site:

https://www.hi.no/hi/nettrapporter?query=&serie=imr-pinro

4.1 Hydrography

Text by: A. Trofimov and R. Ingvaldsen

Figures by: A. Trofimov

4.1.1    Geographic variation

Horizontal distributions of temperature and salinity are shown for depths of 0, 50, 100 m and near the bottom in Figs 4.1.1.1–4.1.1.8, and anomalies of temperature and salinity at the surface and near the bottom are presented in Figs 4.1.1.9–4.1.1.12. The anomalies have been calculated using the long-term means for the period 1991–2020.

In August–October 2025, surface temperature was on average 1.9°C higher than the long-term mean all over the surveyed area, with the largest positive anomalies (>3°C) in the southeastern Barents Sea (Fig. 4.1.1.9). Compared to 2024, the surface temperature in 2025 was much lower (by 1.4°C on average) in most of the area (85%), with the largest negative differences (>2°C in magnitude) in the south and west. Positive differences (0.6°C on average) were mainly found in the northern and southeastern parts of the sea.

Arctic waters were mainly found, as usual, in the 50–100 m layer north of 77°N (Fig. 4.1.1.3 and 4.1.1.5). Temperatures at depths of 50 and 100 m were higher than the long-term means (on average, by 0.7 and 0.6°C respectively) in about two thirds of the surveyed area, with the largest positive anomalies (>1°C) at 50 m depth in the western, southernmost and southeastern Barents Sea. Negative anomalies (on average, −0.4°C at 50 m and −0.3°C at 100 m) were mostly found in the central part of the sea. Compared to 2024, the 50 and 100 m temperatures in 2025 were higher (on average, by 0.9 and 0.7°C respectively) in half of the surveyed area (mainly in the western, southern and southeastern parts), with the largest positive differences (>2°C) at 50 m in the southeast. Negative differences were mainly observed in the central and northern Barents Sea. Small temperature anomalies and differences between 2025 and 2024 (both negative and positive, <0.5°C in magnitude) occupied from 46 to 56% of the area.

Bottom temperature was in general 0.7°C above average in 75% of the surveyed area, with the largest positive anomalies (>1°C) mainly in the southeast (Fig. 4.1.1.10). Bottom waters in 2025 were 0.8°C warmer than in 2024 in 63% of the surveyed area, with the largest positive differences (>2°C) in the southeastern Barents Sea. The negative differences were mainly found in the northwestern and northern parts of the sea. Small temperature anomalies and differences between 2025 and 2024 (both negative and positive, <0.5°C in magnitude) occupied 53 and 63% of the surveyed area respectively. In August–October 2025, the area covered by bottom water with temperatures below zero was 25% in the Barents Sea (71–79°N 25–55°E) being 6% lower than that in the previous year.

Surface salinity was on average 0.4 higher than the long-term mean in about 70% of the surveyed area, with the largest positive anomalies (>0.8) in the northern (east of the Svalbard/Spitsbergen Archipelago) and southeastern (southwest of the Novaya Zemlya Archipelago) Barents Sea (Fig. 4.1.1.11). Negative anomalies (–0.1 on average) were mainly observed in the southern part of the sea. In August–October 2025, surface waters were on average 0.4 saltier than in 2024 in 68% of the surveyed area, with the largest positive differences (>0.8) in the southeast. They were fresher (on average, by 0.2) mainly in the central Barents Sea.

Salinity at 50 m depth was higher than average (by 0.1 on average) in two thirds of the surveyed area, with the largest positive anomalies (>0.1) southeast of the Spitsbergen Archipelago. The largest negative anomalies (>0.1 in magnitude) were found in the southernmost Barents Sea. In August–October 2025, waters at 50 m depth were saltier (by 0.1 on average) than in 2024 in 56% of the surveyed area, with the largest positive differences (>0.2) in the southwesternmost and southeasternmost parts of the sea. At a depth of 50 m, both positive and negative anomalies and differences were larger than at 100 m. Small salinity anomalies and differences of <0.1 in magnitude occupied about 70 and 90% of the area at depths of 50 and 100 m respectively.

Bottom salinity was slightly lower than average in 55% of the surveyed area, with the largest negative anomalies (>0.1 in magnitude) in the southeast (Fig. 4.1.1.12). Positive anomalies of more than 0.1 were mainly found south of the Svalbard/Spitsbergen Archipelago, over the Spitsbergen Bank. In August–October 2025, bottom waters were a bit saltier than in 2024 in 68% of the surveyed area. As a whole, bottom salinity anomalies and differences were small (<0.1 in magnitude) almost all over the area (83 and 90% respectively).

.

4.1.2    Standard sections

Tab. 4.1.2.1 shows mean temperatures in the main parts of standard oceanographic sections of the Barents Sea, along with historical data back to 1965.

The Fugløya–Bear Island and the southern part of the Vardø–North sections cover the inflow of Atlantic and Coastal water masses from the Norwegian Sea to the Barents Sea. The mean Atlantic Water (50–200 m) temperature in the inflow region to the Barents Sea, i.e. at the Fugløya–Bear Island section, was 0.1°C higher than the long-term mean (1991–2020) but 0.8°C colder than in 2024 (Tab. 4.1.2.1). Slightly further east, in the southern part of the Vardø–North section, temperatures were also higher than the long-term mean (0.6°C) but lower than in 2024 (0.4°C) (Tab. 4.1.2.1).

The Kola and Kanin sections cover the flow of coastal and Atlantic waters in the southern Barents Sea. In late August, the Atlantic water temperature in the 0–50 and 50–200 m layers in the Kola section was 1.0 and 0.5°C higher than the long-term mean (1991–2020) respectively (Tab. 4.1.2.1). Compared to 2024, the upper 50 m layer was 0.4°C colder whereas the deeper 50–200 m layer was 0.7°C warmer. In the Kanin section, the mean temperature of the whole water column in early September was 1.4 and 0.7°C higher than the long-term mean (1991–2020) in the shallow inner and deeper outer parts of the section respectively (Tab. 4.1.2.1). Compared to 2024, the water column was warmer by 2.5°C in the inner part and by 0.6°C in the outer part.

Since 2012–2014, the hydrographic monitoring in the northern Barents Sea was strengthened by extending the Vardø–North section all the way up to 81°N, and by establishing a new standard section north of Svalbard (the Hinlopen section). Both sections are to be sampled in late September – early October. The northern part of the Vardø–North section covers mainly Arctic waters, and the temperatures were at the same level in 2025 as in 2024 (Tab. 4.1.2.1).  The Hinlopen section covers the Atlantic Water flowing along the slope toward the deep Arctic Ocean. The temperatures in this section were that the highest that has been observed during the sampling period (2014-2025). ​​​​​​​

4.2. Anthropogenic pollution

4.2.1 Marine litter

Text by: T. Prokhorova, B. E. Grøsvik, R. Klepikovskiy

Figures by: D. Prozorkevich

Surface observations of litter were carried out along the known-length transects of observations from marine mammal observers from Norwegian and Russian vessels. Some observations were made between the transects, so these data were not used in calculations.

Plastic was the most frequent material type of floating litter observations (77.1 % of observations) (Fig. 4.2.1.1). The maximum surface observation of plastic litter was 0.005 m³ per nautical mile (m3/nm), and the average was 0.001 m³/nm. Fishery related litter was recorded in 43.2 % of plastic litter observations at the surface (Fig. 4.2.1.2). Fishery related plastic was represented by ropes, pieces of nets and floats/buoys. Fishery plastic maximum and average volume was 0.005 m³/nm and 0.001 m³/nm, respectively, and it is larger than non-fishery plastic (maximum and average observations of 0.004 m3/nm and 0.0005 m³/nm, respectively).

Wood (wooden sticks, pallets and logs) was recorded in 15.6 % of the surface litter observations. The maximum observation of wood was 0.03 m³/nm, with the average of 0.006 m³/nm. It should be noted that wood is the natural type of litter and biodegrades naturally in the environment.

Metal, paper and rubber were observed singularly (2.1-3.1 % of the observations).

Observations of litter from the trawl transects were done during the survey. Onboard the Norwegian vessels litter from trawls were recorded according the ICES manual for seafloor litter data collection and reporting from demersal trawl samples (ICES Techniques in Marine Environmental Sciences. November 2022. Vol. 67). Onboard the Russian vessels a detailed description of the litter was carried out.

Anthropogenic litter was observed in 17.4 % of pelagic trawl stations during the survey (Fig. 4.2.1.3). Plastic usually is the most frequent material type observed in pelagic trawls and constituted 92.6 % of the observations (it was recorded in 16.1 % of all pelagic trawls). Weight of plastic litter from pelagic trawls varied from 0.0001 kg per nautical mile (kg/nm) to 0.022 kg/nm, with an average of all plastic observations of 0.003 kg/nm, and of all pelagic trawl stations of 0.0005 kg/nm. Fishery related litter (such as ropes made from synthetic fibres and pieces of fishing net) constituted 40.0 % of litter registrations from pelagic trawls (Fig. 4.2.1.4).

Other types of litter in pelagic trawls were metal (observed in 1.6 % of pelagic trawl stations and constituted 9.3 % of the litter observations), textile (in 1.3 % and in 7.4 % correspondingly) and rubber (was found only in one pelagic station). Weight of textile varied from 0.001 kg/nm to 0.005 kg/nm, weight of metal from 0.01 kg/nm to 0.02 kg/nm. It should be noted that textile is a natural product, e.g. ropes made from natural fibres (such as cotton, sisal, hemp, or coir) or all types of clothing (textile and woven products).

From the bottom trawls, 18.6 % of the stations contained litter (Fig. 4.2.1.5). Plastic was the most frequently observed material in the bottom trawls as in the pelagic (90.9 % of stations with observed litter and 16.9 % of the bottom trawls). Weight of plastic litter in bottom trawls varied from 0.0004 kg/nm to 0.766 kg/nm, with an average of 0.049 kg/nm in all bottom trawl stations, and of 0.008 kg/nm in bottom trawls with plastic registrations. Fishery related litter constituted 68.3 % of registrations from bottom trawls (Fig. 4.2.1.6).

Metal was found in 2.0 % of bottom trawl stations (in 10.6 % bottom trawls with litter registrations), weight of metal was from 0.001 kg/nm to 1.25 kg/nm. Textile belong to categories of natural product. It was observed in 1.1 % of bottom trawl stations (in 6.1 % bottom trawls with litter registrations). Weight of textile in bottom trawls varied from 0.006 kg/nm to 0.178 kg/nm. Other material types of litter observed in bottom trawls are rubber (was found at 2 stations) and unrecognisable items (at 1 station). It should be noticed that wood was not registered in bottom trawls during the survey in 2025, and this is the first time without such recordings during marine litter observations in the Barents Sea since 2010. 

5.1 Phytoplankton

Text and figures by: S. Lerch

5.1.1  Data collection

Samples used to characterize phytoplankton community composition and abundance were collected from a total of 116 stations over the course of three separate cruises. Microscopy and algae-net samples were collected from Hinlopen and Vardø-Nord Utvidet transects in October during the ecosystem cruise (cruise numbers: 2025102001, 2025002010), and Fugløya-Bjørnøya during Spring transect cruises conducted in April (cruise number: 2025002004) and June (cruise number: 2025002006). Microscopy was used to identify and quantify taxa in 32 preselected stations along the transects (Fig. 5.1.1). Algae-net samples, used to qualitatively evaluate community composition, were collected from 22 stations. In addition to the samples collected on fixed transects, samples for metabarcoding were collected from 81 stations in September from planned ecosystem cruise stations (cruise number: 2025001013). A subset of metabarcoding samples will be sequenced and analyzed as a part of a three-year time series characterizing phytoplankton community composition in the Barents Sea.

Samples for algal cell counts (100 ml) were taken from 10 m CTD collected water and fixed in Neutral Lugol. Microscope counts were performed following the Utermöhl (1958) method on CTD samples to quantify abundance and community composition at the IMR Flødevigen Plankton Laboratory. Qualitative Algae-net samples were collected using a vertical net tow (10 μm mesh; 0.1 m² opening; 30-0 m), fixed with 2 ml 20% formalin in a 100 ml bottle and stored for future use. Metabarcoding samples were collected by filtering approximately 2 L of seawater, pre-filtered with 180 µm mesh, on to 25 mm filters with a pore size of 5 µm. Samples were then stored at -80 °C until DNA extraction and subsequent sequencing.

Microscopy algal counts include heterotrophic, mixotrophic, and autotrophic taxa, these communities will therefore be referred to as microplankton in the summarized results below.

5.1.2  Results

Based on microscopy counts, the average concentration of Barents Sea microplankton in October was 3.77×10⁵ ± 2.13×10⁵ cells L-1. The average community was numerically dominated by flagellates (56%, 2.13×10⁵ ± 1.32×10⁵ cells L^-1) and cryptophytes (20%, 7.47×10⁴ ± 8.66×10⁴ cells L^-1).

Microplankton abundances and communities varied spatially across the Barents Sea in October (Fig. 5.1.2). Cell concentrations varied by an order of magnitude between stations with a minimum concentration of 9.05×10⁴ cells L^-1 and maximum of 8.67×10⁵ cells L^-1. Higher concentration stations were generally found on the southern section of the Vardø-N Utvidet transect. In contrast to other stations, unclassified cells comprised large proportion of the Hinlopen station communities, these are likely flagellates whose flagella have fallen off.

Within these data diatoms are the only purely photosynthetic group described at a high taxonomic level. In October diatom abundances were relatively low (<1×10⁵ cells L^-1), with the most abundant stations found on the southern section of the Vardø-N Utvidet transect and Hinlopen stations nearest to the Svalbard/Spitsbergen coast (Fig. 5.1.3). Leptocylindrus and Dactyliosolen dominated the high abundance stations on Vardø-N. In contrast, the higher abundance stations on Hinlopen were split across multiple genera including Cylindrotheca, Pennales, Skeletonema, and Eucampia.

The combination of early (April) and late (June) spring sampling along the Fugløya-Bjørnøya transect allows us to describe the evolution of the spring bloom microplankton cell concentrations and community composition. Cell concentrations increased during the course of the spring with average cell concentrations of 3.89×10⁵ ± 3.41×10⁵ cells L^-1 in April and 1.31×10⁶ ± 1.88×10⁶ cells L^-1 in June, although June samples were characterized by greater intra-station variability (Fig. 5.1.4). At the broad taxonomic group level, April communities were dominated by flagellates and cryptophytes while haptophytes were more abundant in June. The high cell concentrations of haptophytes at the northernmost station in June document the occurrence of a Phaeocystis bloom, a common Spring bloom species in the Barents Sea.

5.2. Mesozooplankton biomass and geographic distribution

Text by: E. Bagøien and I. Prokopchuk

Figurs by: E. Bagøien

Mesozooplankton sampling stations during the joint Norwegian-Russian Barents Sea ecosystem cruise in 2025 are shown in Fig. 5.2.1. In the Norwegian sampling area the WP2 net (opening area ~ 0.25 m²) was applied, while in the Russian sampling area the Juday net (opening area ~ 0.11 m²) was used. Both gears were rigged with nets of mesh-size 180 mm and hauled vertically from near the bottom to the surface. The WP2 and Juday nets provide roughly comparable results with respect to mesozooplankton biomass and species composition (Skjoldal et al., 2019). The Norwegian biomass samples are dried before weighing, while the Russian samples are preserved in 4% formalin and their wet weight determined. Dry-weight is then estimated by dividing the wet-weight by a factor of 5.

The spatial distribution of total mesozooplankton biomass shown in Figure 5.2.1 is based on a total of 307 stations, of which 173 were sampled by the Norwegian vessels and 134 by the Russian vessel. Within the western part of the Barents Sea as represented by the Norwegian WP2 samples, the average biomass was 6.9 (± 5.1 SD) g dry-weight m-2. The average zooplankton biomass for the samples within the eastern part of the Barents Sea as represented by the Russian Juday samples was 8.2 (± 5.3 SD) g dry-weight m^-2. All stations shown in Fig. 5.2.1 are included in the 2025 biomass averages here presented. Note that 10 stations in the central Barents Sea were sampled both by IMR and PINRO (not shown). In these specific cases the IMR data were excluded from Fig. 5.2.1 as well as the calculations of biomass given above.

The time-periods for zooplankton sampling by the Russian (26. Aug – 13. Oct 2025) and Norwegian (28. Aug – 3. Oct 2025) vessels were similar. Comparison of average biomasses across years is vulnerable to differing area coverages. Challenges in covering the same area over a series of years are inherent in such large-scale monitoring programs, and interannual variation in ice-cover and logistical issues are two of several reasons for this. To improve the regularity of the sampling grid of the survey area in 2025, stations along the Hinlopen Strait section located between Svalbard/Spitsbergen and Nordaustlandet (Svalbard/Spitsbergen) as well as the Vardø-North section that crosses the central Barents Sea, were excluded from Fig. 5.2.1 as well as the calculations of biomass averages. Differences in spatial coverage among years, as well as spatial variability in station density within the survey region will impact biomass estimates, and particularly so in an environment characterized by large-scale patterns in biomass distribution. Hence, the average biomasses for the Norwegian and Russian main areas as presented here are not directly comparable with those from earlier years.

Such challenges fall outside the scope of this cruise-report, but are addressed in other fora, for instance by analysing time-series within spatially consistent sub-areas.

The overall distribution patterns show similarities across years, although some interannual variability is apparent. In 2025 we observed the familiar pattern of comparatively high biomasses in the southwestern region, and northeast and east of Svalbard/Spitsbergen, as well as the deeper parts of the southeastern region. The biomasses were very low in the central regions including the bank areas, and in the southeastern corner of the Barents Sea (Fig. 5.2.1).

Several factors may impact the levels of zooplankton biomass in the Barents Sea;

• Advective supply of zooplankton from the Norwegian Sea
• Local zooplankton production rates – which are linked to temperature, nutrient conditions and primary production rates
• Predation from carnivorous zooplankters (jellyfish, krill, hyperiids, chaetognaths, etc.)
• Predation from planktivorous fish including capelin, young herring, polar cod, juveniles of cod, saithe, haddock, and redfish
• Predation from marine mammals and seabirds

5.3 Macrozooplankton

5.3.1.  Distribution and biomass of euphausiids

Text by: E. Eriksen, A. Dolgov, D. Prozorkevich and T. Prokhorova

Figures by: S. Karlson

Biomass estimates were calculated by different software during the last four decades: Excel (up to 2017) and R (since that). The new 15 subareas, based on similar environmental status, were used since 2018 (Fig. 5.3.1), while two in the northeast seldom have observations. These areas were used to get more detailed information about the distribution of the krill within the survey area.

In 2025, euphausiids (krill) were widely distributed in the western and central Barents Sea with higher abundance in the southwest (Fig. 5.3.1.1). The biomass values in the upper 60 m are presented as grams (wet weight) per square meter (g/m²). In 2025, the night catches (mean 1.97 g/m²), were much lower than long term mean (7.3 g/m²).

Based on the euphausiid species identification in 2025, Meganyctiphanes norvegica were widely observed in the Barents Sea, while Thysanoessa inermis were mainly observed in the central and northern areas. Two catches of Thysanoessa raschii were taken in the southwest and one in the Great Bank (Fig. 5.3.1.2). The smaller T. longicaudata were also found in 2025.

In 2025, the calculated total biomass of krill was 6.5 million tonnes which was lower that long term mean (fig. 5.3.1.3).

Krill were captured at fewer number of trawl stations than in previous years, and especially east of Svalbard/Spitsbergen and in the southern Barents Sea, indicating possible high predation pressure from capelin and young herring respectively.

Spatial distribution of euphausiids biomass across 15 polygons in the Barents Sea (August–October, 2003–2025) are shown in Fig. 5.3.1.4.

5.3.2 Distribution and biomass indices of pelagic amphipods (mainly Hyperiids)

Text by: E. Eriksen, A. Dolgov, D. Prozorkevich, T. Prokhorova and S. Karlson

Figures by: B. Husson and S. Karlson

Estimation of pelagic amphipods biomass for the Barents Sea was performed in R (see above) and presented here for the period 2003-2025.

In 2025, amphipods generally occurred east of Svalbard/Spitsbergen archipelago and few catches were also taken in the northern and central areas (Fig. 5.3.2.1).

In 2025, amphipods taken Svalbard/Spitsbergen were mostly represented by the Arctic species Themisto libellula (Figure 5.3.2.2). The cosmopolitan species Hyperia galba were found in southwestern and north central areas. At two stations smaller Themisto abyssorum (with max measured length of 15.0 mm) were taken, while they are less captured by the trawl than larger T. libellula (with max measured length of 35.0 mm).

The calculated total biomass of amphipods in 2025 in the upper 60 m was 37.1 thousand tonnes, which is the lowest observed (Fig. 5.3.2.3). 

Text by: E. Eriksen, S. Carlson, D. Prozorkevich, T. Prokhorova and A. Dolgov

Figures by: E. Eriksen and S. Carlson

The biomass of gelatinous zooplankton was calculated using SAS (for the new 23 fisheries subareas, 1980-2017). The new 15 subareas, based on environmental status and bathymetry, were used from 2018 to present spatial variation of jellyfish abundance and biomass (Fig. 5.4.1.). However, two polygons in the northeast seldom have observations.

R-script has been developed for three years, and during the last year some flaws in calculations were corrected. Thus, the biomass shown in previous reports may slightly differ from the latest one.

Here, we presented the time series for biomass indices calculated by SAS (1980-2017) and by R (2018-2025).

The biomass of gelatinous zooplankton was calculated using SAS (for the new 23 fisheries subareas, 1980-2017). The new 13 subareas, based on environmental status and bathymetry, were used from 2018 to present spatial variation of jellyfish abundance and biomass (Fig. 5.4.2.). R-script has been developed for three years, and during the last year some mistakes in calculations were corrected. Thus, the biomass shown in previous reports may slightly differ from the latest one.

Here, we presented the time series for biomass indices calculated by SAS (1980-2017) and by R (2018-2025).

The moon jellyfish (Aurelia aurita) was found at 39 stations in the southern Barents Sea with an average biomass of 14.6 tonnes per sq nmi (Fig. 5.4.2). This is the highest biomass of A. aurita ever observed.

Blue stinging jellyfish, Cyanea lamarckii, was found at 25 stations in the southwestern Barents Sea with average biomass 72.4 kg per sq nmi. C. lamarckii has been observed regularly in the Barents Sea in recent years and the presence of this warm-temperate species may be linked to the inflow of Atlantic water masses.

Ctenophores were found at 15 stations in the southern Barents Sea, and at six of these stations the ctenophores were also identified to genus level (Beroe spp.), commonly known as the cigar comb jellies. The average biomass was 60 kg per sq nmi and at five of these stations the calculated biomass was between 77 and 348 kg per sq nmi, that was also unusually high.

Biomass indices were calculated as total, for large jellyfish, dominating by C. capillata, small jellyfish dominating by A. aurita and unidentified jellyfish for the period 2004-2025. In 2025, total jellyfish biomass in the Barents Sea was much lower than in previously two years and was 2.746 million tonnes (Fig. 5.4.3). However, the proportion of small jellyfish increased from a few to 25% of the total jellyfish biomass index. Jellyfish biomasses dominated by biomasses of large jellyfish (2.0 million tonnes), although biomass of small jellyfish (dominated by Aurelia aurita) was the highest recorded (703 thousand tonnes, Fig. 5.4.3).

Geographical distribution of jellyfish, mainly C. capillata, showed decrease in all areas, except Bear Island Trench in 2025 (Fig. 5.4.4).

Figures by: D. Prozorkevich

Area coverage and estimations

In 2025, the overall coverage of the 0-group distribution was good, with the exception of the polar cod distribution areas in east and the northeastern parts of the Barents Sea (Fig. 6.1). This area has usually not been surveyed in recent years due to time constraints. The abundance and biomass of the zero-group fish were previously calculated using various software packages: SAS&MSAccsess (1980-2015), MatLab (2016-2019), and R (2019-2025). A re-estimation of the zero group time series from BESS using StoX is almost complete and will be presented in a separate report, with the aim to implement it as official estimate from next year.

6.1  Capelin (Mallotus villosus)

Capelin were distributed widely, but for the most part at low densities (Fig. 6.1.1), in accordance with an abundance estimate below average (Fig. 6.1.2). The distribution indicates that some capelin were outside the survey area in the north. The highest densities were observed in the central part and north of Svalbard/Spitsbergen.

6.2  Cod (Gadus morhua)

Cod were widely distributed in the Barents Sea but in low densities. The highest densities were found in the southeast and northwest parts of Barents Sea, and some fish were likely distributed outside the survey area (Fig. 6.2.1). In accordance with the low densities, the abundance estimate indicated a poor year class of cod in 2025 (Fig. 6.2.2).

6.3. Haddock (Melanogrammus aeglefinus)

Haddock were distributed in the western and central parts of the Barents Sea, mainly west of 40°E (Fig. 6.3.1). High densities were not observed in the survey area. In accordance with low densities, the abundance estimate was low indicating a low 2025 year class (Fig. 6.3.2).

6.4  Herring (Clupea harengus)

Distribution of herring was limited to a very small area (Fig. 6.4.1), with the highest densities northwest of Svalbard/Spitsbergen. The abundance in 2025 was extremely low, and far below the long term level (Fig. 6.4.2).

6.5  Polar cod (Boreogadus saida)

Polar cod were found around the Svalbard/Spitsbergen and in the eastern Barents Sea in 2025 (Fig. 6.5.1). There is an increasing shift northwards in the distribution of zero group polar cod. Coverage of the 0-group polar cod was not complete, and especially the eastern parts of the Barents Sea lacked coverage (Fig. 6.5.1). As a consequence, the south-eastern component of the polar cod is not fully represented here. The abundance estimate was slightly below the long term average, but given the lack of coverage in potentially important distribution areas, the true abundance is higher than estimated and year class strength is possibly strong in 2025 (Fig.6.5.2). It should be noted that estimates of the year class strength of polar cod is associated with high uncertainty.

6.6.  Saithe (Pollachius virens)

In 2025, there were hardly any 0-group saithe sampled, only a few specimens were caught (Fig. 6.6.1). This could be due to an abnormal saithe distribution (e.g. in coastal areas outside the survey coverage area) and/or a poor year class.

6.7.  Redfish (mostly Sebastes mentella)

0-group redfish were found close to the north of the Norwegian coast and around Svalbard/ Spitsbergen in 2025. High densities were observed around Svalbard/Spitsbergen (Fig. 6.7.1). The 2025 abundance is the highest in 5 years and slightly above the long-term average (Fig. 6.7.2).

6.7.  Greenland halibut (Reinhardtius hippoglossoides)

0-group Greenland halibut was found on several stations around of  Svalbard/Spitsbergen in 2025 (Figure 6.8.1). Greenland halibut is typically distributed in the fjords of Svalbard/Spitsbergen or in deep depths in the open sea, but 0-group survey provide information about overall distribution, which reflects the abundance of year-classes, can be some signal for assessed. No successful generations of halibut have been recorded in recent years.

6.9.  Long Rough dab (Hippoglossoides platessoides)

The 0-group of long rough dab (LRD) was widely distributed from northwest to southeast, with the highest densities observed in the central part of the Barents Sea.

No numbers estimate was made for 2025, but compared to previous years, the 2025 year-class appears to be very numerous and above long-term average level. Large numbers of 0-group LRD were also caught in bottom trawls catches supporting that they were numerous this year.

Figures by S. Karlson, G. Skaret

7.1    Capelin (Mallotus villosus)

The coverage of the capelin distribution in 2025 was synoptic with high effort allocated to the important bank areas. The capelin coverage was considered to be close to complete (see Fig. 7.1.1.1). A summary of the capelin stock assessment for 2025 is given in Advice on fishing opportunities for Barents Sea capelin in 2026 | Havforskningsinstituttet with more details provided in Barents Sea Capelin | Havforskningsinstituttet.

7.1.1    Geographical distribution

The geographical distribution of capelin recorded acoustically is shown in Fig. 7.1.1.1. The capelin was distributed further south than in 2024, and notably there were very small amounts of capelin in the Great Bank area and east of the Russian/Norwegian boundary. Significant capelin recordings north and west of Svalbard/Spitsbergen have been made in this survey in recent years and were made also this year. 

7.1.2  Abundance by size and age

A detailed summary of the acoustic stock estimate is given in Tab. 7.1.2.1, and the time series of abundance estimates is summarized in Tab. 7.1.2.2. A comparison between the estimates in 2025 and 2024 is given in tab. 7.1.2.3 with the 2024 estimate shown on a shaded background.

The total stock in the covered area was estimated to about 339 thousand tons, which is only about 13% of the long-term average level (2.71 million tons). About 37 % (124 thousand tons) of the 2025 stock had length above 14 cm and was therefore considered to be maturing. The contribution to the total in biomass and numbers was highest from 1 and 2-year-olds (table 7.1.2.1). The biomass of all year classes was less than the long-term average and for 2 and 3-year-olds, the biomass was 10% or less than the long-term average (table 7.1.2.2).

Average weight at age increased compared to 2024 for the age groups 1, 3 and 4. For 3- and 4-year-olds it was still well below the long-term average, whereas it was above the long-term average for 1 and 2-year-olds (fig. 7.1.2.1 and tab. 7.1.2.2).

Estimates based on Target strength (TS) Length (L) relationship: TS= 19.1 log (L) – 74.0