IDENTIFYING MIGRATION FATE AND FACTORS CONTRIBUTING TO MORTALITY OF ATLANTIC SALMON SMOLTS

Abstract

Atlantic Salmon populations are in decline throughout their native distribution largely due to poor estuarine and marine survival. Predation is a significant source of salmon smolt mortality during migration from freshwater to marine environments. This thesis investigates potential mechanisms of predation and other mortality in a population of Endangered inner Bay of Fundy Atlantic Salmon smolts over three years. Predated smolts were identified through the use of novel acoustic predation tags combined with machine learning algorithms trained to differentiate predator and prey behaviour. From 2017 to 2019, survival rates increased as predation rates decreased. Migration rate was identified as a behavioural mechanism of mortality where slower migrating smolts were more likely to be predated. No physiological mechanism of mortality was identified through analyses of host gene expression and pathogen presence. Predation of salmon smolts in this population is highly variable between years and appears to be more opportunistic than selective.