The long-term variation of the mean biomass of the NW, SW and the total Barents Sea show strong correlations (Figure 5.3.1). This might indicate that the western Barents Sea are driven by a factor common for the total Barents Sea. If comparing fluctuations of bottom temperature (Figure 5.3.1) with the benthos biomass (Figure 5.3.2) both shows clear decreasing values during 2007-2010. But previous studies show that benthos has a delay of approximately 3-7 years for macrobenthos to environmental variables (Lyubina et al., 2013; Denisenko, 2013), but with the more long-lived megabenthos, we suggest this delay to no less than 7 years.
If we use a maximum delay of 7 years, we see a direct correlation between temperature and benthos biomass.
Figure 5.3.1. The interannually mean biomass fluctuation of the SW (red, all <1T catches of sponges excluded) and NW (green) from 2005–2016. The dotted line is the Barents Sea mean biomass (see also Figure y3). NW = 74–80°N and 15-40°E but excluding all stations W and N of Svalbard, SW = 65– 74°N and 10–40°E. All stations west and north of Svalbard and all sponge catch >1T excluded.
Figure 5.3.2. Bottom temperature fluctuations of the SW, NW, SE, and NE Barents Sea from 2000 to 2016. NW = 74–80°N and 15–40°E but excluding all stations W and N of Svalbard. NE = 74–80°N and 40–62°E, SW = 65–74°N and 10–40°E, SE = 65–74°N and 40–62°E.
The SE are experiencing high level of commercial trawling which might, together with possible effect from temperature, be part of the explanation to the low benthos-biomass in this area. This become more evident when the SE is compared to the high biomass of benthos in the NE which have no trawling activity (Ljubin et al., 2011).
The highest biomass (sponge catch >1T excluded) in the Barents Sea was recorded in the NE (>60 kg/n.ml). The area of reduced benthos biomass after 2013 (black arrows in Figure 3.4.3 for 2013–2016) are overlapping with the maximum distribution of the snow crab (Figure 3.4.8), the period of maximum consumption/killing (Figure 4.2.5), but also with an increasing bottom temperature from 2007 (Figure 3.1.9b). We therefore suggest the strong decrease in benthos biomass to be an effect multiple impact factors.
Figure 5.3.3. The interannually mean biomass fluctuation of the SE (red line with yellow circles) and NE (blue, box is total mean biomass, diamonds is without the biomass of the snow crab). The dotted line is the Barents Sea mean biomass (see also Figure y3). NE = 74–80°N and 40–62°E, SE = 65– 74°N and 40–62°E.