Deliverable 6.12 Impact of climate change on Greenland ecosystems and fish resources

A detailed understanding of how anthropogenic activities affect ecosystems and the services they provide is essential for sustainable management. However, assessments of the impact of multiple drivers on complex ecosystems is often challenged by lack of data at the relevant spatio-temporal resolution or knowledge of interactions among drivers.

The SW Greenland coast and shelf is important for the industrial and sustenance fishing that is essential for Greenland. Here, we aim to describe decadal changes of the ecosystem and identify key drivers. To describe ecosystem dynamics we analysed changes in the 33 species of demersal fish found in 5713 bottom trawls collected on the shelf from 1993 to 2016. We find substantial
increase in average biomass combined with increases in average individual weight, average trophic level and composition of dominant species. Using previous studies as a baseline we interpret the observed changes as a partial recovery of an over-exploited system. Sea ice cover, run-off from the Greenland Ice Sheet, seafloor trawling and water mass distribution are all known drivers of ecosystem change in the study area. Although, the impact of each driver varies over the last 2-3 decades all appear to facilitate increase in fish biomass. Climate change-related melting of sea ice and the Greenland Ice Sheet likely sustained increased primary production by increasing light and nutrient availability. Increases in temperature and salinity indicates increased inflow of Atlantic water, which increase connectivity to lower latitude systems. Finally, decreased trawling effort combined with mitigation measures to decrease by-catch may have decreased fish mortality. This suggest that a combination climate change and long-term hydrographic variability may have facilitated the recovery of fish stocks. Finally, the massive changes observed in fish biomass, size and trophic level of the fish community is likely to be a strong driver for cascading effects to other components of the SW Greenland shelf ecosystem.