Tapeworm Parasite Burden Is Linked to Diet, Body Size, Condition, Growth, Restocking and Habitat Use in Piscivorous Salmonids of a Subarctic Lake

ABSTRACT Parasites affect hosts in interaction with the entire ecological community. This is particularly evident for trophically transmitted parasites, such as Dibothriocephalus tapeworms, which infect multiple intermediate fish hosts, potentially reducing their fitness and suitability for human consumption. Here, we used a large, multi‐year dataset to examine ecological underpinnings between Dibothriocephalus burden and host traits and diet. In particular, we assessed relationships between parasite burden and body size, body condition, growth, restocking origin and stomach contents in the key piscivorous salmonids, Arctic charr ( Salvelinus alpinus ) and brown trout ( Salmo trutta ), in a large subarctic lake, Lake Inari. We found that Dibothriocephalus prevalence was similarly high in both salmonids, with decreasing parasite burden over the years. In both species, larger individuals and those having three‐spined ( Gasterosteus aculeatus ) and/or ninespine ( Pungitius pungitius ) stickleback remnants in their stomachs had a higher parasite burden, whereas better body condition, quicker growth, stomach contents other than sticklebacks, stocked origin (in Arctic charr) and river habitat (in brown trout) were associated with lower parasite counts. These findings suggest that Dibothriocephalus burden is likely to be costly, while successful foraging on non‐stickleback food is associated with lower burden. Overall, the results highlight the intricacy of trophic accumulation of Dibothriocephalus parasites, with sticklebacks playing a special role in their transmission.