Photo: Rudi Caeyers - UiT

Several sea birds species have had dramatic population declines and will be vulnerable for additional threats, like oil pollution (Fauchald et el 2019).

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Sea anemone. Photo: Haakon Hop, Norwegian Polar Institute

With retreating sea ice, new areas in the northern Barents Sea become available for fisheries, including bottom trawlers. Of special interest to WGIBAR is therefore the vulnerability analysis (Jørgensen et al., 2015).

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Polar cod. Photo: Fredrik Broms, Norwegian Polar Institute

The Barents Sea polar cod stock was at a low level in 2017 and 2018. Norway conducted commercial fisheries on polar cod during the 1970s; Russia has fished this stock on more-or-less a regular basis since 1970. However, the fishery has for many years been so small that it is believed to have very little impact on stock dynamics. Stock size has been measured acoustically since 1986, and has fluctuated between 0.1–1.9 million tonnes. Stock size declined from 2010 to a very low level in 2015, increased to 0.9 million tonnes in 2016, and again declined to 0.4 million tonnes in 2017. The rate of natural mortality for this stock appears to be quite high, relative to its importance as prey for cod and different stocks of seals.
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Photo: Fredrik Broms, Norwegian Polar Institute

In order to conclude on the total impact of trawling, an extensive mapping of fishing effort and bottom habitat would be necessary. In general, the response of benthic organisms to disturbance differs with substrate, depth, gear, and type of organism (Collie et al. 2000). Seabed characteristics from the Barents Sea are only scarcely known (Klages et al. 2004) and the lack of high-resolution (100 m) maps of benthic habitats and biota is currently the most serious impediment to effective protection of vulnerable habitats from fishing activities (Hall 1999). An assessment of fishing intensity on fine spatial scales is critically important in evaluating the overall impact of fishing gear on different habitats and may be achieved, for example, by satellite tracking of fishing vessels (Jennings et al. 2001). The challenge for management is to determine levels of fishing that are sustainable and not degradable for benthic habitats in the long run.

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Capelin. Photo: Fredrik Broms, Norwegian Polar Institute

Stock size fluctuations

The Barents Sea capelin has undergone dramatic changes in stock size over the last three decades. Three stock collapses (when abundance was low and fishing moratoriums imposed) occurred during 1985–1989, 1993–1997, and 2003–2006. A sharp reduction in stock size was also observed during 2014–2016; followed by an unexpectedly strong increase during 2016–2017. Observed stock biomass in 2015 and 2016 was below 1 million tonnes, which previously was defined as the threshold of collapse, while stock biomass increased to above 1 million tonnes in 2017-2018.  Despite indications that capelin stock size was underestimated in 2016, at present 2015–2016 is recognized as a ‘mini-collapse’.

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Cod, polar cod and capelin. Photo: Geir Wing Gabrielsen, Norwegian Polar Institute

The interaction cod-capelin-polar cod is one of the key factors regulating the state of these stocks. Cod prey on capelin and polar cod, and the availability of these species for cod varies. Сod can strongly influence on numbers of these species. In the years when the temperature was close to the long-term mean, the cod overlap with capelin and polar cod was lower than in the recent warm years. Cod typically consume most capelin during the capelin spawning migration in spring (quarters 1+2), but especially in recent years the consumption has been high also in autumn (quarters 3+4) in the northern areas (Figure 4.2.3). In 2017-2018 capelin consumption by cod was stable.

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Benthos habitat. Photo: Haakon Hop, Norwegian Polar Institute

In most of the measured by BESS years, the biomass in the northeast part of the Barents Sea was above the total Barents Sea mean (Figure 4.6.1), but from 2013 and ongoing, the mean biomass was reducing, and was record low (<20 kg/nm) in 2016, and below the total Barents Sea mean. As one of the reasons of this decrease could be assumed develop of snow crab population and it predation on the benthos (including juvenile stages of the megabenthic animals.

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