Behavioural responses of wild anadromous Arctic char experimentally infested in situ with salmon lice

Salmon lice can impact the marine behaviour, growth, and survival of salmonids, but little is known about their effects on Arctic char. We present behavioural responses from the first dose-response experiment with wild anadromous Arctic char (n = 50) infested in situ with salmon lice (0.0–1.2 lice g−1 fish) in an area with low natural infestations. Infested fish spent less time at sea (mean ± SD = 22 ± 6 d) than non-infested fish (mean ± SD = 33 ± 5 d), and a significant dose response was evident, with even very low louse burdens (−1 fish) reducing the marine feeding time. Furthermore, a negative correlation was present between time spent close to their native watercourse and parasite burden, suggesting that salmon lice influence the marine habitat use of Arctic char. No impact of salmon lice was evident on the return probability, i.e. marine survival. However, the presence of louse-induced mortality cannot be excluded as the modest sample size was only sufficient to detect extreme effects. Reduced marine feeding time and altered marine habitat use will likely have substantial negative effects on growth and fitness, suggesting that impacts of salmon lice must be considered in the conservation of anadromous Arctic char