Abstract
BackgroundThe effect of individual acoustic receiver contributions to animal positioning is a crucial aspect for the correct interpretation of acoustic positional telemetry (APT). Here, we evaluated the contribution of each receiver within two APT designs to the number of tag signals detected and the position accuracy of free-ranging Atlantic cod, through data exclusion of single receivers from the analysis. The two APTs were deployed around offshore (ca 50 km) wind turbines at which 27 individual cod were tagged.ResultsWe found that the exclusion of data from an APT receiver that was positioned within the movement area of the individual fish reduced the number of tag signals detected and the position accuracy of the set-up the most. Excluding the data from a single receiver caused a maximum of 34% positions lost per fish and a maximum increase in core area of 97.8%. Single-receiver data exclusion also caused a potentially large bias in the reconstruction of swimming tracks. By contrast, exclusion of a receiver that was deployed within 50 m from a turbine actually improved fish position accuracy, probably because the turbine can cause signal interference as a reflective barrier.ConclusionsWe recommend that an exploratory small-scale study like the one presented here be conducted before embarking on a larger-scale APT study. By excluding the data of single receivers from the positioning analysis, we were able to explore the suitability of a receiver set-up for the movement patterns of our target species. Furthermore, when a receiver is lost from an APT during deployment, the data should be treated with care as our results show that changes in triangulation outcome can lead to considerable differences in swimming tracks and home range estimates.
Highlights
The effect of individual acoustic receiver contributions to animal positioning is a crucial aspect for the correct interpretation of acoustic positional telemetry (APT)
We evaluated the contributions of individual receivers to the detection rate and position accuracy within two acoustic positional telemetry (APT) designs for Atlantic cod at a wind farm in the Belgian Part of the North Sea (BPNS)
We aimed to answer the following questions: do individual receivers contribute to the spatial data collection and position accuracy? Which local factors explain variation among individual receivers? To what extent is the reconstruction of fish swimming tracks affected by data exclusion from individual receivers? We addressed these questions by quantifying the effects of simulated data exclusion of single receivers on cod detection and positioning data
Summary
The effect of individual acoustic receiver contributions to animal positioning is a crucial aspect for the correct interpretation of acoustic positional telemetry (APT). Habitat-specific features (e.g., vegetation type and density, bottom characteristics, the presence of rocks and man-made obstacles) can block signal propagation [15] Natural events such as currents and surface waves can influence receiver detection range [12, 16] and lead to signal interference through receivers getting temporarily buried or even lost [17]. If this occurs, an APT setup may suffer significantly in terms of the number of tag signals detected and position accuracy. Before embarking on a large-scale study, exploring the effects of excluding the data from a receiver on the overall results can greatly facilitate the design of a cost-efficient ATP set-up and enhance understanding of the consequences of receiver loss
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