Set for success: ecological factors facilitating restoration of self-sustaining Lake Trout (Salvelinus namaycush) populations in acid-damaged lakes

Abstract

Sudbury, Ontario, Canada is a site of extreme biodiversity loss due to widespread acidification from over a century of metal mining and smelting. Lake trout (Salvelinus namaycush) were the most widely and severely impacted of the resident sportfish but with massive emission reduction in recent years, their populations have since shown significant signs of recovery. The objective of my study was to identify conditions associated with lake trout recolonization and recruitment by conducting fish and water quality surveys on 31 oncedamaged lakes across Sudbury’s historic acid deposition zone. Lake trout biomass and odds of lake trout recruitment success increased in lakes with more depth of usable lake trout habitat, higher zooplankton biomass and a lower concentration of dissolved organic carbon. A history of hatchery stocking of lake trout was a top predictor of total lake trout biomass in standardized gillnet surveys but did not emerge in top models for predicting natural recruitment or the total biomass of natural lake trout in the lake. These results demonstrate the importance of lake-specific ecological factors in the reestablishment of lake trout populations, regardless of whether the source of the population was hatchery stocking, migration from neighbouring lakes or residual populations that survived acidification. Overall, my study shows evidence that Sudbury’s historically damaged lakes have been extensively recolonized and are no longer limited by acidic conditions. In many cases, they have shifted to simplified fish communities in which zooplankton may be a primary prey source for lake trout. Water chemistry factors, in particular the increase in concentration of dissolved organic carbon and the associated decrease in water clarity also emerged as potential factors shaping lake trout recovery in my study lakes.