Foraging mode of cave-dwelling Arctic charr in the Lake Mývatn area
Foraging mode, the behavioural tactics adopted by animals when searching for and attacking prey, yield important insights into how animals vary in the use and exploitation of their local habitats. In this study, we examined the foraging mode, feeding behaviour and aggression for 55 Arctic charr (fork length = 5.0-17.0 cm) in four lava caves in the Lake Mývatn area. As expected from fish in lentic waters, the cave-dwelling Arctic charr were highly mobile during prey search (median=80.1% of the time) and prior to prey attack (median=73.0%). Majority of foraging attempts were directed towards the water surface (mean=73.0%), but to a lesser degree towards benthic prey (mean=16.4%) or prey in the water column (mean = 10.6%). A substantial variability was detected among individuals, as many fish directed their foraging efforts toward prey in only one of the three sub-habitats. Finally, the fish varied greatly in the number of agonistic acts encountered with other fish (0-27.2 acts/30 min), which also increased with individual mobility and the proportion of surface feeding. This study yields an important first step in understanding how behaviour contributes to the survival and local adaption of small benthic Arctic charr in unique habitats such as lava caves.