Salmon Lice (Lepeoptheirus salmonis) Increase Age-at-maturity in Atlantic Salmon (Salmo salar) by Decreasing Growth: An Estimate of Parasite Effects on Host Growth

The decline in wild Atlantic salmon stocks throughout the North Atlantic has been linked to the complex interactions between these fish in all life stages of their life and numerous anthropogenic activities. One noteworthy interaction is between salmon lice and Atlantic salmon, as some of the declines have been linked back to increases in parasite abundance. However, it is unclear how salmon lice can impact changes in the life-history traits of Atlantic salmon. Here, I use data from a long-term field study to show that salmon lice decrease the growth rate of wild fish, causing them to mature at an older age and size. I also build a size-structured population model and use it to quantify the difference in growth rate between a group of fish treated and untreated for salmon lice. My findings are consistent with predictions of life-history theory, that hosts can alter life-history traits in response to parasitism. Considering the indirect effects of parasitism on critical life-history traits will give better insight into the resilience of wild populations and help improve management strategies.M.Sc.2021-07-28 00:00:0