Receiver tilt: a scourge for aquatic telemetry or useful predictor variable

Abstract

BackgroundWater current data can be a useful predictor variable to include in acoustic telemetry studies given its link to changes in fish behaviour. While there are a range of sensors which can measure currents, they are often expensive and logistically difficult to deploy and maintain. Contemporary acoustic receivers measure tilt angle which may act as a proxy for water current data if the receiver is moored on a rope and buoy system and allowed to sway in the direction of water flow. We tested the relationship between tilt angle and water current by co-locating two types of commonly deployed receivers with current meters.ResultsBoth receivers (Vemco VR4 and VR2AR) displayed similar ranges in tilt angle. While the VR4 could only measure tilt on a daily basis, the VR2AR measurements were taken hourly; these data were then also aggregated on a daily scale. A positive relationship was found between the tilt angle for both types of receivers and current speed, including for both aggregated daily and hourly data for the VR2AR. Both receivers tended to slightly over-estimate current at lower speeds and underestimate it at high speeds.ConclusionsThese data show tilt angles recorded by commonly deployed receivers could be incorporated as a proxy for current flow where dedicated current loggers are absent. We would recommend programming receivers to record tilt as frequently as possible to account for short-term variability in environmental conditions.