During the 2018 Barents Sea Ecosystem Survey (BESS) 83 fish species from 28 families were recorded in pelagic and bottom trawl catches, some taxa were recorded at genus or family level only (Prokhorova et al 2019).
L.L. Jorgensen (IMR), N.A. Strelkova (PINRO)
Benthos is an essential component of the marine ecosystems. It can be stable in time, characterizing the local situation, and is useful to explain ecosystem dynamics in retrospect. It is also dynamic and shows pulses of new species distribution, such as the snow crab and the king crab, and changes in migrating benthic species (predatory and scavenger species such as sea stars, amphipods and snails with or without sea anemones). The changes in community structure and composition reflect natural and anthropogenic factors. There are more than 3000 species of benthic invertebrates registered in the Barents Sea (Sirenko, 2001), but here we only present the megafaunal component of the benthos collected by trawl and registered (species, abundance and biomass) during the Barents Sea Ecosystem Survey (BESS). This includes mainly large bodied animals with long lifespans. This investigation was initiated in 2005 only – a short timeline relative to investigations related to plankton and fish. Accordingly, interpretation of long-term trends for megabenthic data must be pursued with caution.
The ongoing warming were associated with increased water and air temperature, larger area covered by Atlantic and Mixed warm water masses and decreased ice coverage. The warming was also associated with
increased macro zooplankton such as krill and jellyfish biomass, increased fish recruitment (age 0) which trigger positive development of fish stocks (cod, haddock, deep water redfish, capelin and herring). Increased production and adequate fishing pressure in relation to stock size led to cod and haddock stock size increasing to record high levels and the capelin stock withstanding the high predation level. Several sea birds populations from coastal colonies stay or migrate in to the Barents Sea to feed and moult, possibly increasing the total number.
Most Barents Sea fish species are demersal (Dolgov et al., 2011); this fish community consists of about 70–90 regularly occurring species which have been classified into zoogeographic groups. Approximately 25% are either Arctic or mainly Arctic species. The commercial species are all boreal or mainly boreal species (Andriashev and Chernova, 1995), except for Greenland halibut (Reinhardtius hippoglossoides) that is classified as either Arcto-boreal (Mecklenburg et al., 2013) or mainly Arctic (Andriashev and Chernova, 1995).
Mesozooplankton biomass in the Norwegian part of the Barents Sea in 2018 was slightly above the long-term average for the last 20 years. The mesozooplankton biomass in “Atlantic” subareas of the Barents Sea in 2018 were at similar levels as in previous years, and has shown declining trends on the Central Bank and Great Bank subareas since the peak in 1995. Krill biomass has shown an increasing trend during the last decades. Jellyfish biomass in 2017 was at its third highest level since 1980 – but could not be estimated for 2018.
The Barents Sea has been divided into 15 subareas or polygons (Figure 2.1.1). The division is based on topography and oceanography and is a modification (with some subdivision) of the system used by Eriksen et al. (2017) in a summary analysis of pelagic biomass. The four western areas, South-West, Bear Island Trough, Hopen Deep and Tor Iversen Bank, are areas covered mainly with Atlantic water and constitute the inflow region of Atlantic water with the splitting of the current branches east through the Kola Section (south of the Central Bank) and north in the Hopen Deep (west of the Central Bank).
Zero-group fish are important consumers of plankton and are prey for other predators, and, therefore, are important for transfer of energy between trophic levels in the ecosystem. Estimated total biomass of 0-group fish species (cod, haddock, herring, capelin, polar cod, and redfish) varied from a low of 165 thousand tonnes in 2001 to a peak of 3.4 million tonnes in 2004 with a long-term average of 1.7 million tonnes (1993-2017) (Figure 3.5.1). Biomass was dominated by cod and haddock, and mostly distributed in central and northern-central parts of the Barents Sea.
The phytoplankton development in the Barents Sea is typical for a high latitude region with a pronounced maximum in biomass and productivity during spring. During winter and early spring (January-March) both phytoplankton biomass and productivity are quite low. The spring bloom is initiated during mid-April to mid-May and may vary strongly from one year to another. The bloom duration is typically about 3-4 weeks and it is followed by a reduction of phytoplankton biomass mainly due to the exhaustion of nutrients and grazing by zooplankton. Later in the fall when the increasing winds start to mix the upper layer and bring nutrients to the surface, a short autumn bloom can be observed. However, the time development of this general description can vary geographically. The spring bloom in the Atlantic water domain without sea-ice is thermocline-driven, whereas in the Arctic domain with seasonal sea-ice, stability from ice-melt determines the bloom (Skjoldal and Rey 1989, Hunt et al. 2012). Thus, the spring bloom at the ice edge in the Barents Sea can sometimes take place earlier than in the southern regions due to early stratification from ice melting.