Performance and reliability of active acoustic biotelemetry to best track marine pelagic species in temperate coastal waters

Abstract

Acoustic tracking is a commonly used method to study the movement ecology of marine species. The characteristics of the data collected are not simply functions of the location of the tagged animal as they are also influenced by the method of data collection and its sampling frequency. In particular, since the data are acoustically driven, the significance of any result hinges not only on the accuracy of the equipment but also on the reliability of the information received. While passive acoustic telemetry requires an evaluation of the detection efficiency of receivers moored in different habitats (or sites) to obtain reliable data, active acoustic telemetry requires more field-related information on how to best track tagged animals without impacting on their natural behaviour. This study aimed to evaluate the reliability of active acoustic telemetry data in a temperate coastal environment. This was achieved by conducting a series of field experiments to assess (i) the use of signal strength-to-infer distance to the tracked animal under different tracking conditions, (ii) what signal strength threshold can be used to obtain reliable bio-telemetered data, (iii) whether the behaviour of a tracked animal would be a main concern in terms of data reliability, and (iv) the best filtering option to reduce the data to be analysed. The findings yielded a signal strength-to-distance relationship to improve the accuracy of the positional fixes of actively tracked animals, which can be used as a practical reference for future tracking studies on pelagic species in temperate coastal environments.