Quantifying salmon survival from river exit to return as adult: Collecting thermal and behavioural data to refine smolt to adult survival indices

SMOLTrack IV started in January 2021 and will end in December 2023.

There is significant mortality in the oceanic phase of Atlantic salmon. The studies into causes and consequences have primarily been done by modelling because detailed information about salmon behaviour and migration routes in the Ocean is scarce. Classic expeditions by ship are prohibitively expensive and restricted both in time and space and are also to some extent catch-per-unit effort limited. Telemetry has proven to be the only viable method to get detailed knowledge of this behaviour.

In recent years a few studies using satellite tags have been published, giving information on salmon migration at sea. Unfortunately, the current PSAT tags are too large to deploy on smaller fish (i.e. smolts), hence the preferred animals to tag are large kelts and the PSATs are typically limited to a 12 month deployment. Hence, there is still a lack of behavioural data, especially for the smaller life stages, and there is a limitation in data describing the return migration from the feeding grounds in the Northern Atlantic.

Acquiring detailed information from salmon behaviour at sea is a challenge and will require a multifaceted approach. The project aims to investigate the post-smolt behaviour during migration from coastal areas to the feeding grounds in the north Atlantic. Additionally, the project aims to identify and evaluate the potential for ‘fit for purpose tagging’ in the North Atlantic, using insight gained from pilot studies undertaken in previous SMOLTRACK projects. Identifying ways to obtain detailed knowledge on coastal and ocean behaviour and migration will be a pre-requisite for a greater understanding of the factors governing behaviour and ocean survival for Atlantic salmon and can feed directly into fisheries management strategies that may optimise and naturally enhance the probability of wild adult returns.