Design and Evaluation of the Efficacy of Neutrally Buoyant, Externally Attached Acoustic Tags

Each year, thousands of juvenile salmonids are surgically implanted with telemetry tags to monitor their movements and survival through several hydroelectric projects in the Columbia and Snake Rivers.  Previous research has shown that tag burden (mass of tag relative to mass of the fish) is an important factor in predicting the occurrence of barotraumas and associated mortality when juvenile salmonids pass through hydroelectric turbines.  Fish with higher tag burdens are more likely to be injured or killed as they pass through hydroelectric turbines, thus biasing survival studies.  In order to mitigate the effects of tag burden, a neutrally buoyant and externally attached acoustic transmitter was developed for use on juvenile Chinook salmon.  In the laboratory, two methods of attachment and tag designs were evaluated (i.e., anterior to dorsal fin, through dorsal musculature underneath fin) for tag retention, tissue damage and mortality over a 14 day holding period.  In addition, tag retention and tissue damage were measured for fish experiencing different levels of shear force (i.e., 10ft/sec, 30ft/sec, and 40ft/sec), similar to that experienced during hydroturbine passage.  There were no mortalities or tag loss observed during the study period and throughout all holding.  The results of the current study show that a neutrally buoyant, externally attached acoustic tag is a promising new design that could be employed in hydroturbine passage related studies, however, further laboratory and field testing is required.