A Field Evaluation of an External and Neutrally Buoyant Acoustic Transmitter for Juvenile Salmon: Implications for Estimating Hydroturbine Passage Survival

Richard S Brown,Martin L Ahmann,Jayson J Martinez,Katrina V Cook,Z Daniel Deng,Brett D Pflugrath,Tao Fu,Huidong Li,Xinya Li,Adam G Seaburg,Bradly A Trumbo,Mark R Muldoon

doi:10.1371/journal.pone.0077744

Abstract

Turbine-passed fish are exposed to rapid decreases in pressure which can cause barotrauma. The presence of an implanted telemetry tag increases the likelihood of injury or death from exposure to pressure changes, thus potentially biasing studies evaluating survival of turbine-passed fish. Therefore, a neutrally buoyant externally attached tag was developed to eliminate this bias in turbine passage studies. This new tag was designed not to add excess mass in water or take up space in the coelom, having an effective tag burden of zero with the goal of reducing pressure related biases to turbine survival studies. To determine if this new tag affects fish performance or susceptibility to predation, it was evaluated in the field relative to internally implanted acoustic transmitters (JSATS; Juvenile Salmon Acoustic Telemetry System) used widely for survival studies of juvenile salmonids. Survival and travel time through the study reach was compared between fish with either tag type in an area of high predation in the Snake and Columbia rivers, Washington. An additional group of fish affixed with neutrally-buoyant dummy external tags were implanted with passive integrated transponder (PIT) tags and recovered further downstream to assess external tag retention and injury. There were no significant differences in survival to the first detection site, 12 river kilometers (rkm) downstream of release. Travel times were also similar between groups. Conversely, externally-tagged fish had reduced survival (or elevated tag loss) to the second detection site, 65 rkm downstream. In addition, the retention study revealed that tag loss was first observed in fish recaptured approximately 9 days after release. Results suggest that this new tag may be viable for short term (<8 days) single-dam turbine-passage studies and under these situations, may alleviate the turbine passage-related bias encountered when using internal tags, however further research is needed to confirm this.

Highlights

All hydro turbine-passed fish are exposed to a rapid decrease in pressure
A telemetry tag implanted inside the coelom of small fish such as juvenile salmon could increase the likelihood of injury or mortality following exposure to rapid decompression [8]
Using experimental pressure scenarios that simulate turbine passage, Carlson et al [8] determined that the probability of mortal injury varies with tag burden

Summary

Introduction

All hydro turbine-passed fish are exposed to a rapid decrease in pressure. Rapid pressure changes can result in injuries such as swim bladder rupture, exophthalmia, emboli, and hemorrhaging [1,2,3,4,5]. The excess mass (difference between the gravitational and buoyant forces acting on an object or in this case weight in water) of an implanted tag has been shown to lead to an increase in swim bladder volume; that is, a fish increases displacement to balance the additional mass [9], [10]. This increased volume of gas in the swim bladder leads to a higher likelihood that fish will suffer barotrauma when the gas expands during rapid decompression associated with turbine passage [11,12]

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