The effect of an externally attached neutrally buoyant transmitter on mortal injury during simulated hydroturbine passage

Abstract

On their seaward migration, juvenile salmonids commonly pass hydroelectric dams. Fish passing through hydroturbines experience a rapid decrease in pressure as they pass by the turbine blade. The severity of this decompression can be highly variable but can result in injuries such as swim bladder rupture, exophthalmia, and emboli and hemorrhaging in the fins and tissues. Recent research indicates that the presence of a telemetry tag (acoustic, radio, inductive) implanted inside the coelom of a juvenile salmon increases the likelihood that the fish will be injured or die during turbine passage. Thus, previous turbine passage survival research conducted using telemetry tags implanted into the coelom of fish may have been inaccurate. Therefore, a new technique is needed to provide unbiased estimates of survival through turbines. This study evaluated the effectiveness of a neutrally buoyant externally attached acoustic transmitter on decompression-stressed juvenile Chinook salmon. Both nontagged fish and fish tagged with a neutrally buoyant external transmitter were exposed to a range of rapid decompressions simulating turbine passage. Juvenile Chinook salmon tagged with a neutrally buoyant externally attached acoustic transmitter did not experience a higher degree of barotrauma-induced injuries than their nontagged counterparts. We suggest that future research include field-based comparisons of survival and behavior among fish tagged with a neutrally buoyant external transmitter and those internally implanted with transmitters.