Environmental influence on transmitter detection probability in biotelemetry: developing a general model of acoustic transmission

1. Environmental factors, such as wind, may have a strong influence on the detection probability and detection rate of acoustic telemetry tags. The effect of environmental factors may obscure biological effects and distort the interpretation of acoustic telemetry data. 2. This study was undertaken with fish internally tagged with acoustic transmitters containing depth sensors and monitored by an array of automatic receivers. The influence of environmental factors on the hourly detection rate was evaluated using environmental data from a nearby climate station. The signal detection probability was modelled within the framework of general theory of sound propagation in water. 3. Wind was found to have the strongest influence on the detection rate. Transmitter depth range and rain also contributed significantly to the variation in detection rate. 4. By modelling the attenuation coefficient as a function of wind speed, we show that the probability of detecting a free-swimming acoustically tagged animal can be successfully modelled using general sound propagation theory. 5. The approach of modelling detection probability as a function of the attenuation coefficient offers a wide applicability, as it implies a direct link between detection probability and physical characteristics of the water at the study site. Correcting for varying detection probability is in many cases extremely important to do, since rhythms in biological/behavioural factors are often confounded with environmental variables that influence detection probability (e.g. sea breeze, tide).