The area covered in 2020 are given in Fig. 3.5.1.4, and 3.5.1.5. In contrast to previous years, the station grid in 2020 covered the entire Barents Sea shelf, including the upper bathyal slope north to FJL. Russian and Norwegian experts were involved in the megabenthos by-catch processing and distributed on the BESS vessels (RV “G.O. Sars”, RV “Kronprints Håkon”, SRV “AtlantNIRO”, and SRV “Vilnus”). On the Norwegian vessel “Johan Hjort” megabenthos was only processed to large animal groups due to a lack of skilled benthic experts onboard.
Benthos and shellfish
Benthos
The status of megabenthos in 2020
The area covered in 2020 are given in Fig. 3.5.1.4, and 3.5.1.5. In contrast to previous years, the station grid in 2020 covered the entire Barents Sea shelf, including the upper bathyal slope north to FJL. Russian and Norwegian experts were involved in the megabenthos by-catch processing and distributed on the BESS vessels (RV “G.O. Sars”, RV “Kronprints Håkon”, SRV “AtlantNIRO”, and SRV “Vilnus”). On the Norwegian vessel “Johan Hjort” megabenthos was only processed to large animal groups due to a lack of skilled benthic experts onboard.
The main results of the BESS 2020, compared with 2019 and long-term average value, are given in table 3.5.1.1 and shown in Fig. 3.5.1.4, and 3.5.1.5.
Table 3.5.1.1 – The main characteristics of the megabenthic by-catches (excluding Pandalus borealis) during BESS 2019, 2020, and average long-term values for the period 2005-2019; the minimum-maximum / average±standard error* nm – nautical mile
** calculated as the interannual average value of interstation mean values for each year during the period 2005-2019
Figure 3.5.1.4 – The A) number of taxa per station, B) number of individuals and C) biomass per nautical mile according to BESS 2019 (upper row) and 2020 (lower row). The northern shrimp Pandalus borealis (a semi pelagic species) are excluded (but see chapter 3.5.2 in this report). Inter-annual pattern. The species diversity (611 taxa) in 2020 was above the 2019 value (621 taxa) and higher than long-term average (433 taxa) (Table 3.5.1.1). The spatial distribution of species-number (number of taxa per station) in 2020 was generally the same as the long-term pattern, except for the low species number in the areas covered by “HJ” where benthic expertise was absent. High number of taxa were recorded in the western part of the sea, while low numbers in the east, especially in the Pechora Sea area. (Fig. 3.4.1.4 A).
In the Norwegian part of the survey, the spatial distribution of both abundance and biomass was approximately similar to 2019, though low biomass in the north. On the Russian part of the survey, there was a large decrease in both biomass and abundance (Fig. 3.4.1.4 B and C).
Long-term trends in distribution of the megabenthic biomass.
Because colonial and fragmented species are difficult to count, biomass of the total benthos catch is use in detecting long-term BESS variations in megabenthic communities.
Spatial distribution.
The monitoring series of the megabenthos biomass-distribution shows relative stable large-scale patterns, with high biomass particularly in the southwest; and another, but much more variable, high biomass in the northeast. The central Barents Sea are highly variable in biomass but do never reach the highest or lowest recoded values in the Barents Sea (Fig. 3.5.1.5).
In 2020, the southwestern and northeastern margins of the Barents Sea shelf had areas with high biomass that was made up by dense sponge aggregations. An area with high biomass was also recorded in the red king crab distribution area near Kanin Nos peninsula. But, in contrast to many previous years, the hot spot of the biomass in the Novaya Zemlya shallows (in the area of the snow crab dense population) was not recorded in 2020 (Fig. 3.5.1.5).
Figure 3.5.1.5. Distribution of the megabenthos biomass (excluding Pandalus borealis) in the Barents Sea from 2005 to 2020. Explaining the background for the variability is difficult do to the relatively short time-series. But Fig. 3.5.1.5 also illustrates the deficiency and fault in the megabenthos assessment for several years. In 2005, 2014 and 2018 there were a lack of station coverage in the Norwegian or Russian areas. In 2019, the north-eastern part of the sea was incompletely covered. In 2014, 2015, 2016 and 2019 the Loophole area was not sampled because a commercial snow crab fishery. In 2012 and probably 2017 the biomass was overestimated in the Russian zone due to technical issues with the trawl tuning. Such lack of coverage and non-standardised processing should be taken into account when analysing the megabenthic time series.
In 2020 the benthos station coverage was good on the Norwegian part of the survey, even though there were defects in the taxonomic processing of the material. On the Russian side does the persistently low values give reason to speculate if there could be a new technical flaw with the trawl gear on the Russian vessels.
Inter-annual fluctuation of the mean megabenthos biomass.
To make an estimation of the long-term dynamics of the megabenthos, inter-annual changes of the mean biomass were calculated for the total Barents Sea, and thereafter expressed for four separate areas of the sea – northeast, northwest, southeast and southwest (Fig. 3.5.1.6).
The fourteen years of monitoring (though inconsistent in area-coverage) reveal a moderate, positive trend of increasing megabenthic biomass during the period 2010 2018 when calculated for the “total Barents Sea” (Fig. 3.5.1.6 B).
Fluctuation of total biomass of megabenthos is positive correlated (r = 0.59 for "total") with the water temperature on the Kola Sections (0-200 m depth layer, st. 3-7, Fig. 3.5.1.6 A), but with a time lag of about 7 years (ICES, 2020).
Similar response to change of environmental conditions was documented for the Barents Sea macrobenthos, but with a delay in approximately four years (Lubina et al., 2012, 2016; Denisenko, 2013). Difference in duration of the time lag between macro- (grab’s) and mega- (trawl’s) benthos is caused by different mean size and longevity of the lifespan of these size groups of benthic organisms causing a faster life-turnover for small organisms.
In 2020 mean biomass both for totally Barents Sea (Fig. 3.5.1.6 B) and for all four sectors (Fig. 3.5.1.6 C and D) decreased. According to the hypothesis about 7year time-lag correlation between megabenthic biomass and water temperature, this fall in biomass in 2020 can be the result of the fall in temperature during 2013-2014 (see arrow in Fig. 3.5.1.6 A).
Figure 3.5.1.6 Variations of the average annual temperature in the water layer 0-200 m in the 3-7 stations of the Kola Section (A) and the inter-annual fluctuation of the mean megabenthos biomass in total Barents Sea (B) and in it western (C) and eastern (D) sections. Biomass of Pandalus borealis and all catches more than 1t are excluded.
The dotted line in the plots B, C, and D – no reliable data on mean biomass
“Total” – Barents Sea shelf within 68-80° N, 15-62° E, “NE” – north-eastern sector (74-80° N, 40-62° E), “NW” – north-western sector (74-80° N, 15-40° E), “SE” – south-eastern sector (68-74° N, 40-62° E), “SW” – south-western sector (68-74° N, 15-40° E).
Vulnerable habitats and distribution of their species-indicators
According to the criteria of NAFO (Kenchington et al., 2019) and a few recent publication (Buhl-Mortensen et al., 2019; Burgos et al., 2020), three groups of the Barents Sea megabenthic species can be characterized as indicators of vulnerable habitats: sponge ground, coral gardens, and sea pens fields.
Sponge ground
Sponges are widely distributed on the Barents Sea shelf but does not exceed one kilogram per nautical mile of trawling (Fig. 3.5.1.7). In 2020, as in many previous years, were dense aggregations of sponges exceeding one ton per trawling recorded in the southwestern part of the shelf, at the depth 266-329 m. These sponges were dominated by Geodia barrette, G. atlantica, and G. macandrewii. Dense aggregations of sponges with biomass of 760 kg/nm, and dominated by Stelette rhaphidiophora, Geodia phlegrae, G. parva, and G. hentsheli, were recorded on the upper continental slope north of FJL.
Figure 3.5.1.7 Biomass (kg/nm) distribution of sponges within the Barents Sea shelf according to BESS-2020Coral gardensAmong anthozoans species that forms “coral gardens”, stony cap coral Caryophillia smithii and gorgonian corals Isidella lofotensis and Radicipes sp. were found within the Barents Sea shelf in 2020.
The population of Caryophillia smithii (a hexacorallian solitary stony cap coral with hard internal calcareous skeleton) with biomass below 214 g/nm, was recorded in the southwestern part of the shelf, at the dept 222-393 m (Fig. 3.5.1.8).
Fragments of the Isidella lofotensis (with biomass below 35 g/nm) were recorded in 2020 in ten stations, at the depth 282-912 m, in the main on the upper part of the northern continental slope (fig. 3.5.1.8). Nine individuals of nonbranched gorgonian coral Radicipes sp. with a total biomass of 1.5 g were found in two points at depth 735 and 792 m in the same area.
Figure 3.5.1.8 Biomass (g/nm) distribution of corals Caryophillia smithii, Isidella lofotensis, and Radicipes sp. within the Barents Sea shelf according to BESS-2020Sea-pen fields
Among the tree species of sea pens recorded during BESS-2020, only Umbellula encrinus formed quite dense aggregations. All recordings of Umbellula were concentrated in the northern part of the Barents Sea continental slope, on the Yermak Plato (Fig. 3.5.1.9), and in the western slope of St. Anna Trough. During the BESS-2020 U. encrinus was recorder at 27 stations at the depth in range 335-916 m. The largest biomass recorded in one trawl haul was 22.6 kg/nm.
Figure 3.5.1.9 Biomass (kg/nm) distribution of sea pens Umbellula encrinus within the Barents Sea shelf according to BESS-2020Two other species of sea pens (Funiculina quadrangularis and Virgularia mirabilis) were found in the same area but only in number of a few individuals and grams per station (Fig. 3.5.1.10).
Figure 3.5.1.10 Biomass (g/nm) distribution of sea pens Funiculina quadrangularis and Virgularia mirabilis within the Barents Sea shelf according to BESS-2020The Barents Sea potentially “vulnerable” taxa.
Among the more abundant in the Barents Sea megabenthos species, the potentially vulnerable are soft corals of Nephtheidae family and associated with them large baskets star (a brittle star) of the Gorgonocephalus genera who clings to the Nephtheidae soft coral during its early life cycle.
In the Barents Sea, four valid species of the Nephtheidae soft corals are almost always recorded in the BESS area: Drifa glomerata, Duva florida, Gersemia fruticosa, and G. rubiformis. In 2020 soft corals were recorded in 186 out of 429 stations during the BESS, ranging from 0.1 to 803 g/nm per nm of trawling (average of 84.4 g). According to Fig. 3.5.1.11 are Gersemia fruticosa and G. rubiformis the most abundant in the shelf areas of the sea and while G. fruticose dominated in the north, G. rubiformis prevails in the south.
Figure 3.5.1.11 Biomass (g/nm) distribution of soft corals (Drifa glomerata, Duva florida, Gersemia fruticosa, and G. rubiformis) within the Barents Sea shelf according to BESS-2020In 2020, four valid species of the brittle stars Gorgonocephalus genera were recorded: G. arcticus, G. eucnemis, G. caputmedusae, and G. lamarckii. The most abundant of them are G. arcticus, followed by G. eucnemis. The G. caputmedusae and G. lamarckii were only recorded on four stations in the Norwegian part of the survey (Fig. 3.5.1.12) which may be caused by taxonomic flaws. Gorgonocephalid brittle stars were recorded at 132 out of 429 stations of BESS, from 78 to 916 m depth, and the total biomass of the Gorgonocephalus brittle stars ranged from 0.002 to 51.8 kg/nm per nm of trawling (average of 2.8 kg).
Figure 3.5.1.12. Biomass (kg/nm) distribution of the brittle stars of genega Gorgonocephalus (G. arcticus, G. eucnemis, G. lamarckii, and G. caputmedusae) within the Barents Sea shelf according to BESS-2020Abundant in the Barents Sea big, upraised, and fragile comatulids sea lilies fit the criteria of vulnerable taxa. Two species of the order Comatulida (non-stalked crinoid) are distributed in the shelf area of the Barents Sea.
The bigger and more abundant in the north and central part of the Barents Sea is Heliometra glacialis folloved by smaller and less abundant Poliometra prolixa, in the main distributed in the water to north and east of Spitzbergen (Fig. 3.5.1.13).
Figure 3.5.1.13 Biomass (kg/nm) distribution of the Comatulidae crinoids Heliometra glacialis and Poliometra prolixa within the Barents Sea shelf according to BESS-2020These crinoids were recorded in 2020 at 121 out of 429 stations of BESS, from 80 to 916 m depth, and with total biomass ranged from 0.001 to 4.1 kg/nm per nm of trawling (average of 0.2 kg/nm).
State of selected benthic species
By Aleksei Stesko, Denis V. Zakharov (PINRO), Ann Merete Hjelset, Carsten Hvingel (IMR)
Snow crab
The snow crab (Chionoecetes opilio) is a newly established species in the Barents Sea and was first recorded in May 1996 on the Goose Bank area (Strelkova, 2016). Since then it has increased in both distribution and abundance. In 2012 commercial harvesting of the snow crab started.Regular annual monitoring of the snow crab population began with the Norwegian and Russian Barents Sea Ecosystem Survey (BESS) in 2004. This survey is the most important source of information on snow crab population status in the Barents Sea.
Assessments of snow crab dynamics based on BESS data (Table 3.5.2.1 and Fig. 3.5.2.1 and 3.5.2.2) indicate that in the Barents Sea the snow crab population is still developing (distribution and abundance).
{j apopup type="image" content="images/stories/barentsportal/gallery/WGIBAR2021/tab3521.png" width="800" height="" title="Table 3.5.2.1 Overview of the snow crab catches during BESS in the period 2005-2020"}
Table 3.5.2.1 Overview of the snow crab catches during BESS in the period 2005-2020{/japopup}
Figure 3.5.2.1. The development of the distribution of the snow crab population in the Barents Sea (number of individuals/nm) according to BESS 2019-2020.
Figure 3.5.2.2. The dynamic of the snow crab population in the Barents Sea given as the total number of crabs (blue bars) and the number of trawl hauls with crabs (red line) during the BESS 2005–2020 (2018 covered only small part of snow crabs area, see Fig. 3.4.2.2).In 2020, as in previous years, the densest aggregations of snow crabs (more than 1000 ind/nml) were concentrated in the central part of the Barents Sea in the Loophole area and near Novaya Zemlya archipelago within the Russian Economic Zone (Fig. 3.4.2.3).
Figure 3.5.2.3 Distribution of the snow crab (Chionoecetes opilio) in the Barents Sea in August-October 2019-2020 (BESS data).Size structure of the snow crab population show that abundant generations appear periodically, and that this may affect the overall population dynamics in the Barents Sea. During the ecosystem survey period, abundant generations were recorded with 3 years’ interval - in 2009, 2012, and 2015–2016, 2017-2020 (Fig. 3.5.2.4, Bakanev & Pavlov 2021).
Figure 3.5.2.4 The sex and size structure of the snow crab population from 2009–2020 (Bakanev & Pavlov 2021, with editions), individuals on the Y-axis. Since 2003, snow crabs in the eastern part of the Barents Sea, have been recorded in stomachs of bottom fish species (cod, haddock, catfish, American dub, and starry ray). A new study by Holt et al. (2021) shows that the snow crab is a new prey item for cod. However, it does not represent a prominent component of their diet, less than <10% in the period examined (2003-2018).
Northern shrimp
Northern shrimp (Pandalus borealis) is common and widely distributed in the Barents Sea on the depth (250-350 m) muddy flats of the Barents Sea and in temperatures between -0,5 – 1,5°C (Fig. 3.5.2.6).
Figure 3.5.2.6. Mean biomass (kg per nt ml) per bottom temperature (С°) and depth (m) in the Barents Sea during BESS 2005-2017 (Zakharov 2019)During the 2020 BESS survey, it was recorded at 317 of the 2020trawl stations with a biomass that varied from a few grams to 113.4 kg per nautical mile, with an average catch of 4.6±0.4 kg/nml across 218 station. As in previous years the densest concentrations of shrimp in 2020 were registered in central part of the Barents Sea, around Spitsbergen and in the Franz Victoria Trough (Fig. 3.5.2.7).
Figure 3.5.2.7. Distribution of the Northern shrimp (Pandalus borealis) in the Barents Sea, August–October 2019 and 2020 (D.V. Zakharov, C. Hvingel, 2021, in print). During the BESS 2006-2020 average catches of the shrimp varied from 4 to 11 kg (Fig. 3.5.2.8), all stayed stable around the average level. The increase of biomass in 2017-2018 may be connected with the investigations in northeastern were large biomasses of shrimp were recorded.
Figure 3.5.2.8. Mean catches of the Northern shrimp (Pandalus borealis) in the Barents Sea during the BESS 2006-2018. The red line shows mean value over all years (D. Zakharov, C. Hvingel, 2021, in print). Biological analyses of the northern shrimp population in the eastern part of the BESS were conducted in 2018 by Russian scientists. Similar to 2017, the bulk of the population consisted of younger individuals: males of 12–27 mm carapace length; and females of 17–30 mm carapace length (Fig. 3.5.2.9).
Figure 3.5.2.9 Size and sex structure of catches of the Northern shrimp (Pandalus borealis) in the eastern Barents Sea, August–October 2017–2018 (D.V. Zakharov, C. Hvingel, 2021)State of selected benthic species
Snow crab
The snow crab (Chionoecetes opilio) is a newly established species in the Barents Sea and was first recorded in May 1996 on the Goose Bank area (Strelkova, 2016). Since then it has increased in both distribution and abundance. In 2012 commercial harvesting of the snow crab started. Regular annual monitoring of the snow crab population began with the Norwegian and Russian Barents Sea Ecosystem Survey (BESS) in 2004. This survey is the most important source of information on snow crab population status in the Barents Sea.
Assessments of snow crab dynamics based on BESS data (Table 3.4.2.1 and Fig. 3.4.2.1 and 3.4.2.2) indicate that in the Barents Sea the snow crab population is still developing (distribution and abundance).
Table 3.5.2.1 Overview of the snow crab catches during BESS in the period 2005-2020
In 2020, as in previous years, the densest aggregations of snow crabs (more than 1000 ind/nml) were concentrated in the central part of the Barents Sea in the Loophole area and near Novaya Zemlya archipelago within the Russian Economic Zone (Fig. 3.4.2.3).
Size structure of the snow crab population show that abundant generations appear periodically, and that this may affect the overall population dynamics in the Barents Sea. During the ecosystem survey period, abundant generations were recorded with 3 years’ interval - in 2009, 2012, and 2015–2016, 2017-2020 (Fig. 3.4.2.4, Bakanev & Pavlov 2021).
Since 2003, snow crabs in the eastern part of the Barents Sea, have been recorded in stomachs of bottom fish species (cod, haddock, catfish, American dub, and starry ray). A new study by Holt et al. (2021) shows that the snow crab is a new prey item for cod. However, it does not represent a prominent component of their diet, less than <10% in the period examined (2003-2018).
Northern shrimp
Northern shrimp (Pandalus borealis) is common and widely distributed in the Barents Sea on the depth (250-350 m) muddy flats of the Barents Sea and in temperatures between -0,5 – 1,5°C (Fig. 3.4.2.6).
During the 2020 BESS survey, it was recorded at 317 of the 2020trawl stations with a biomass that varied from a few grams to 113.4 kg per nautical mile, with an average catch of 4.6±0.4 kg/nml across 218 station. As in previous years the densest concentrations of shrimp in 2020 were registered in central part of the Barents Sea, around Spitsbergen and in the Franz Victoria Trough (Fig. 3.4.2.7).
During the BESS 2006-2020 average catches of the shrimp varied from 4 to 11 kg (Fig. 3.4.2.8), all stayed stable around the average level. The increase of biomass in 2017-2018 may be connected with the investigations in northeastern were large biomasses of shrimp were recorded.
Biological analyses of the northern shrimp population in the eastern part of the BESS were conducted in 2018 by Russian scientists. Similar to 2017, the bulk of the population consisted of younger individuals: males of 12–27 mm carapace length; and females of 17–30 mm carapace length (Fig. 3.4.2.9).
