Altering Vertical Placement of Hydroacoustic Receivers for Improved Efficiency in Coldwater Estuary Zones

Abstract

Acoustic telemetry is used to study Atlantic Salmon Salmo salar migration ecology and identify mortality zones within estuary systems. Improved detection efficiency helps reduce the uncertainty associated with survival estimates and improves the accuracy of various migration performance metrics. While emigrating salmon smolts and postsmolts are largely surface-oriented, using the top few meters of the water column, literature suggests they may sound to 10 m or deeper, influencing detection probability and therefore survival estimates. We determined the influence of receiver depth on detection efficiency to improve telemetry assessments in our coldwater estuary zones. We found significant differences in total detections with experimental depths. Detection efficiency of transmitters improved as much as 18.3% when receivers were placed on the bottom and by 9.2% when receivers were placed at 20 m versus 10 m depth. In a second portion of our study, we evaluated the influence of depth and several environmental variables on detection efficiency using sentinel transmitters. Receivers placed at 20 m depth had greater detection efficiencies than receivers placed at 10 m depth during increased precipitation and wind speed events and at all tide stages. Our results can be used to improve detection efficiency of tagged, epipelagic Atlantic Salmon smolts in coldwater estuary zones.

Received November 14, 2016; accepted May 24, 2017Published online August 9, 2017

ACKNOWLEDGMENTS

We thank reviewers M. Renkawitz, D. Stich, and J. Kocik for their thoughtful and insightful reviews of this manuscript and J. Stevens for producing the map. Mention of trade names does not constitute endorsement by the U.S. Government.