Biotelemetry is widely used to study the behaviour and survival of migrating adult Pacific salmon, but little is known about if and how the tagging process and burden of the transmitter pose risks to the study animal. Minimizing the adverse impacts of tagging is important for reasons of animal welfare, but also to derive representative data from tagged individuals. In Chapter 2, I compare the short-term physiological responses of adult sockeye salmon tagged either via gastric insertion or external attachment to untagged controls and report no differences in physiology between the treatment groups. In Chapter 3, I monitored the movement and status of gastrically and externally tagged individuals and reported a significant influence of tag type on survival. These results reveal that the failure to detect immediate physiological and behavioural differences in tagged adult migrating Pacific salmon does not negate the possibility that long-term tag-specific adverse effects may occur.