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

A neutrally buoyant, externally attached acoustic transmitter has shown promise in the laboratory as a novel design for use to monitor the survival and migration of juvenile salmonids through the Snake and Columbia Rivers.  One issue commonly associated with externally attached tags is the effect that it may have on swimming performance (i.e., snags and drag).  As well, the presence of an externally attached telemetry tag may increase the susceptibility to predation, specifically for smaller fish.  Critical swimming speeds (U_crit) of fish tagged with two different neutrally buoyant, external tags were measured in a respirometer and compared to internally and non-tagged juvenile Chinook salmon to determine the tag effects on swimming performance.  U_crit scores were significantly lower for fish externally tagged when compared to control fish.  However, there was no significant difference in U_crit between fish internally implanted with transmitters and those externally tagged.  Predator avoidance of fish tagged anterior to the dorsal fin was then compared to non-tagged individuals to determine if tagged fish were more susceptible to predation due to the presence of the tag.  This was evaluated by comparing the proportion of each treatment group consumed (tagged, non-tagged) during exposure to piscivorous adult rainbow trout.  Results indicate that the presence of the neutrally buoyant, external tag did not result in greater predation susceptibility when compared to non-tagged fish.