Abstract
The effects of increasing fishing pressure in combination with temperature increase in the Nordic and Barents Seas have been evaluated using an end-to-end model for the area forced by a downscaled RCP 4.5 climate scenario. The scenarios that have been applied have used four different fractions of fisheries mortality at maximum sustainable yield (Fmsy); 0.6, 0.8, 1.0 and 1.1 x Fmsy. As it is highly likely that more ecosystem components will be harvested in the future, the four scenarios have been repeated with fishing on a larger number of ecosystem components, including harvesting of lower trophic levels (mesozooplankton and mesopelagic fish). The zooplankton biomass had an increasing trend, regardless of the increase in fishing pressure on their predators. However, when introducing harvest on the lower trophic levels, this increase was no longer evident. When harvesting more components, the negative response in biomass of pelagic and demersal fish to increasing harvest became more prominent, indicating an increasing vulnerability in the ecosystem structure to stressors. Although harvest on lower trophic level led to an immense increase in the total catch, it also resulted in a decrease in the total catches of pelagic and demersal fish, despite more species being harvested in these guilds.
Highlights
Facing climate change and a growing human population, the world’s ocean resources will be put under even higher pressures in the future than they already are
The impact of changing the harvest in the model from historical levels to the fractions of fisheries mortality at maximum sustainable yield (Fmsy) applied in the different scenarios, was more evident in the ‘all in’ scenarios compared to the ‘commercial’ scenarios (Figures 3, 4)
We suggest that the harvest pressure on capelin should be implemented using a version of the escapement rule that leaves at least 200,000 t of capelin to spawn (Gjøsaeter et al, 2015)
Summary
Facing climate change and a growing human population, the world’s ocean resources will be put under even higher pressures in the future than they already are. Cheung et al (2010) showed that highlatitude areas such as the Norwegian and Barents Seas are likely to experience an increase in total catch potential in the future, based mostly on calculations of future primary production, trophic level of the species and its geographic range. This is supported by observations from the Barents Sea over the last decades, where increasing temperatures have been beneficial for e.g., Northeast Arctic cod Gadus morhua (Kjesbu et al, 2014). Changes in fisheries management strategies can be as or more important to the ecosystem as climate change (Groeneveld et al, 2018)
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