Detection efficiency of an autonomous underwater glider carrying an integrated acoustic receiver for acoustically tagged Pacific herring

Abstract

Autonomous underwater vehicles (AUVs) or gliders are increasingly being used with acoustic telemetry to elucidate fish movements while collecting simultaneous environmental data. We assessed the utility of an AUV equipped with an integrated acoustic receiver to detect Pacific herring (Clupea pallasii) in Prince William Sound, AK, USA. A range test evaluated the effect of glider flight characteristics and environmental conditions on the detection efficiency of transmitters at varying depths. While distance from transmitters was the strongest predictor of detections, glider depth had a variable effect on detection efficiency which depended on transmitter depth and dive orientation. The detection efficiency of the glider-mounted acoustic receiver was less affected by wind speed and water level than that of stationary acoustic receivers deployed within the study area. The AUV also performed repeated, adaptive transects in an area of ∼630 km2 area and detected 30 Pacific herring transmitters without a priori knowledge of their locations. Of these herring transmitters, 14 were presumed shed after repeated detections within the same area, and 2 were detected at multiple locations. This study is the first to demonstrate that glider-mounted acoustic receivers have high detection efficiency for transmitters at varying depths and can detect movements of migratory forage fish in large search areas.