The Influence of Tag Presence on the Mortality of Juvenile Chinook Salmon Exposed to Simulated Hydroturbine Passage: Implications for Survival Estimates and Management of Hydroelectric Facilities.

Each year, telemetry tags (acoustic, radio, and passive integrated transponder tags) are surgically implanted into thousands of fish to assess their passage and survival through hydropower facilities. One passage route that is of particular concern is through hydroturbines, where fish may be exposed to a range of potential injuries that include barotraumas from rapid decompression. The change in pressure from acclimation to exposure (nadir) has been identified as an important factor in predicting the likelihood of mortality and injury for juvenile Chinook salmon Oncorhynchus tshawytscha undergoing rapid decompression associated with simulated turbine passage. The presence of telemetry tags has also been shown to influence the likelihood of mortality and injury for juvenile Chinook salmon. We investigated the likelihood of mortality and injury for telemetry-tagged juvenile Chinook salmon that were exposed to a range of pressure changes associated with simulated turbine passage. Several factors were examined as predictors of mortal injury for fish undergoing rapid decompression; of these factors, the log e transformed ratio of acclimation pressure: exposure pressure (LRP) and the tag burden (tag mass expressed as a percentage of fish mass) were the most predictive. As the LRP and tag burden increased, the likelihood of mortal injury also increased. Our results suggest that previous estimates of survival for juvenile Chinook salmon passing through hydroturbines were negatively biased due to the presence of telemetry tags, and this has direct implications for the management of hydroelectric facilities. Realistic examples indicate how the bias in turbine passage survival estimates could be 20% or higher depending on the LRP and tag burden. Negative bias would increase as the tag burden and the pressure change ratio increase and therefore has direct implications for survival estimates. We recommend that future hydroturbine survival studies use the smallest telemetry tags possible to minimize the potential bias associated with tag presence. Received January 9, 2011; accepted October 11, 2011 [ABSTRACT FROM PUBLISHER]