Monitoring mating behaviour of Large Benthic Arctic charr (Salvelinus alpinus) in Thingvallavatn in a context of changing climate and anthropogenic activity

The Arctic region appears to be affected more intensely by Earth’s changing climate than other regions in the Northern hemisphere. Iceland is located on the boundary between sub-Arctic and Arctic zones and is affected by the atmospheric systems and ocean currents from both of these zones. Iceland is an area which is likely to be affected by the climate change-driven impact characteristic of both the Arctic and temperate zones. Arctic charr (Salvelinus Alpinus) in lake Thingvallavatn, Iceland features four pronounced morphs. One of these, the Large Benthic charr (LB charr) spawns between July and September (peaking in early August) which is unusually early for Arctic charr and the maintenance of a healthy population may depend heavily on conditions at a single spawning ground. Pressures driven by climate change and human presence are likely to affect spawning sites, hence it is necessary to establish a baseline for collecting data on the activity of the fish at the spawning-site in order to track potential effects of environmental changes over extended periods of time. Clear water and the fact that spawning takes place during daylight hours made filming of mating behaviour relatively easy. Stationing modern lightweight cameras close to redds (fish nests) allowed us to gather continuous data on mating behaviour and spawning at several redds. The data gathered from video footages was directed at the following questions; i) does male density at redds change with time and if so, how? ii) is the density of males different between redds? iii) Do female and male aggression levels differ among redds? and iv) is the aggression rate at redds dependent on male density? The results suggest that density of fish at redds is dynamic and tend to fluctuate over time. Over the studied redds, the number of fish (including females) at any moment (30 second interval snapshots) ranged from 0 to 7. Female and male aggression frequencies differed significantly (p