Determining Minimum Size Thresholds for Tagging Juvenile Salmonids Using a New Injectable Downsized Acoustic Transmitter

To accurately predict survival using tagged salmonids, it is assumed that marked fish are representative of the untagged seaward-migrating fish.  However, if tag burdens (the ratio of tag mass to fish mass) are too high, tagged fish will be at a disadvantage compared to untagged fish and survival estimates may be biased.  To reduce the negative influence of high tag burdens on the accuracy of survival estimates, research was conducted to produce a down-sized (DS) Juvenile Salmon Acoustic Telemetry System (JSATS) transmitter.  This transmitter weighs less than the currently available 0.304 g JSATS transmitter, likely allowing smaller fish to be studied than is currently possible.  Additionally, the DS JSATS is cylindrical, making it injectable, thus reducing surgery times and fish handling.  Prior to the implementation of full scale research with this new transmitter, laboratory research was conducted to derive appropriate size limits for fish tagging protocols and ensure that the tag burden at these sizes will not negatively influence the growth, survival and performance of study fish.  This process also includes ensuring tagged fish are large enough that the transmitters will not be expelled when seaward-migrating fish are exposed to dynamic riverine environments.  To achieve these goals, growth, survival and tag retention were examined on a range of sizes of juvenile Chinook salmon up to 90 days following tagging and a subset of fish were exposed to conditions simulating dam passage.