Barentsportal
Barentsportal
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).
Although the oil- and gas production in the Barents Sea is relatively small and in limited areas, the increase in ship traffic may add a risk for accidents leading to local oil spills. The increased traffic by cruise ships and fisheries activity in the Svalbard region add to the risk of local breeding populations.
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).
Current knowledge of the response of benthic communities to the impact of trawling is still rudimentary. The benthos data from the ecosystem survey in 2011 have been used to assess the vulnerability of benthic species to trawling, based on the risk of being caught or damaged by a bottom trawl (WGIBAR report 2016). A clear decline in biomass was noted for all three categories when comparing trawled vs. untrawled areas. This suggests that trawling significantly affects the biomass of all species, but predominantly the “high-risk” taxa. Some Barents Sea regions were particularly susceptible to trawling (2016 WGIBAR Report).
Polar cod. Photo: Fredrik Broms, Norwegian Polar Institute
Polar cod. Photo: Fredrik Broms, Norwegian Polar Institute
Not updated as 2017 data for diet of capelin and polar cod were not yet available
Eleven years (2006–2016) of capelin diet were examined from the Barents Sea where capelin is a key forage species, especially of cod. The PINRO/IMR mesozooplankton distribution shows low plankton biomass in the central Barents Sea, most likely due to predation pressure from capelin and other pelagic fish. This pattern was also observed in 2017. In the Barents Sea, a pronounced shift in the diet from smaller (<14 cm) to larger capelin (≥14 cm) is observed.
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).
Capelin. Photo: Fredrik Broms, Norwegian Polar Institute
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’.
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.
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. In 2017, the biomass extremely increased to 116 kg/nm, the highest value recorded over the entire period of BESS (Figure 4.6.1).
Cod. Photo: Fredrik Broms, Norwegian Polar Institute
Cod is the major predator on capelin; although other fish species, seabirds and marine mammals are also important predators. In the last 6–7 years, cod stock levels have been extremely high in the Barents Sea. Estimated biomass of capelin consumed by cod in recent years has been close to the biomass of the entire capelin stock (Figure 4.2.3). Abundance levels of predators other than cod are also high and, to our knowledge, stable.