The Effects of Neutrally Buoyant, Externally Attached Transmitters on Swimming Performance and Predator Avoidance of Juvenile Chinook Salmon

Migrating juvenile salmonids experience rapid decompression that could result in injury or mortality due to barotrauma as they pass turbines at hydropower facilities. Recent research indicates that the risk of injury or mortality due to barotrauma is higher in fish bearing surgically implanted transmitters. Since tagged fish are used to represent the entire population, this tag effect potentially leads to inaccuracies in survival estimates for fish passing turbines. This problem led to development of a novel transmitter, the use of which may eliminate bias associated with the passage of transmitter-bearing fish through turbines. Juvenile Chinook salmon Oncorhynchus tshawytscha were tagged with two different neutrally buoyant, externally attached transmitters (types A and B). The effects of transmitter presence on swimming performance were examined by comparing critical swimming speeds (U-crit; an index of prolonged swimming performance) of externally tagged fish, untagged individuals, and fish that received surgically implanted Juvenile Salmon Acoustic Telemetry System acoustic transmitters. Fish tagged with external transmitters had lower U-crit than untagged individuals. However, there was no difference in U-crit between fish with external transmitter type A or B and fish with surgically implanted transmitters. Testing was conducted to determine whether predator avoidance was affected by the presence of type A transmitters compared with untagged fish. No difference in predation mortality was detected between tagged and untagged fish. Although results suggest that U-crit was affected by externally attached transmitters in comparison with untagged fish, the overall impact as reflected by survival was similar; field-based survival studies involving juvenile salmonids passing through hydroturbines are recommended. The absence of swimming performance effects in fish with external tags relative to fish with internally implanted transmitters and the lack of an increased predation risk relative to untagged fish suggest that an externally attached, neutrally buoyant transmitter is a viable option for telemetry studies in estimating survival of juvenile salmonids passing through hydroturbines.