Evaluating receiver contributions to Acoustic Positional Telemetry: A case study on Atlantic cod around wind turbines in the North Sea
Background: An important aspect for the correct interpretation of Acoustic Positional Telemetry (APT) data concerns the effect of individual receiver contributions to animal positioning. The present study evaluated the contribution of each receiver within two APT designs to set-up efficiency and position accuracy of free-ranging Atlantic cod, through sequential single receiver removal. The two APTs were deployed around offshore wind turbines at which 27 individual cod were tagged and released,
... 0 km offshore, at depths of 20-30 m. Results: Results indicated that removal of an APT receiver, positioned within the movement area of the individual fish, reduced the efficiency and position accuracy of the set-up the most, with a maximum of 34% position loss per fish, and an increase in core area of 97.8%. Removal of a single receiver in general was shown to potentially lead to considerably altered swimming tracks. Additionally, removal of a specific receiver that was deployed within 50 meters from a turbine (i.e. reflective barrier) actually improved fish position accuracy. Conclusions: An explorative, small-scale study like the one presented is recommended, before embarking on any larger scale APT study. Exploration of receiver contributions to set-up performance allow to test the suitability of a receiver set-up for the specific movement patterns and local tracking conditions for a particular target species. Data from receiver arrays from which a receiver was lost should be treated with care, as results revealed that changes in triangulation outcome can lead to considerable shifts in swimming tracks and animal home range estimates.