Effects of a novel acoustic transmitter on swimming performance and predator avoidance of juvenile Chinook Salmon: Determination of a size threshold

The miniaturization of acoustic transmitters enables researchers to tag smaller fish for telemetry studies, thus representing a greater proportion of the population of interest. Fish having a smaller transmitter burden (e.g., the weight of the transmitter relative to the weight of the fish) may also have fewer potential adverse transmitter effects. The development of an injectable acoustic transmitter has led to research that determined the least invasive and quickest method of implantation. Following that research, the objectives of this study were to determine the effects of transmitter implantation on swimming performance and predator avoidance, and to find a minimum size threshold of fish that can be tagged without adversely affecting those responses. To assess critical swimming speed (Ucrit; an index of prolonged swimming performance) and predator avoidance for juvenile Chinook Salmon (Oncorhynchus tshawytscha), fish were split into three treatments: (1) implantation with a dummy injectable acoustic transmitter (IAT treatment), (2) implantation with a dummy injectable acoustic transmitter and passive integrated transponder tag (IAT+PIT treatment), and (3) an untagged control. IAT treatment fish had lower Ucrit values than untagged controls among individuals below 79mm fork length (transmitter burden 3.4–4.0%). Ucrit values for the IAT+PIT treatment were not significantly different from untagged controls and no size threshold was found. There was no significant difference in predator avoidance between fish implanted with the IAT or IAT+PIT compared to untagged controls. These guidelines could provide researchers and managers with a powerful tool to examine behavior and survival of small salmonids.