Effects of season and acoustic telemetry sample sizes on the detections and movements of potadromous common bream Abramis brama in a highly connected wetland system

Abstract Acoustic telemetry is a powerful tool for understanding spatial and temporal fish movements in complex freshwater systems but determining appropriate sample sizes for measuring individual variability in movement metrics is challenging. Here, the movements of 170 common bream Abramis brama were measured over two years in the highly connected River Bure wetland system, eastern England. Analyses of seasonal and spatial movement patterns revealed higher movement metrics in winter versus summer, with the extent of movements measured enabled by the high lateral connectivity of this wetland system, with bream often occupying the numerous off-channel lentic habitats present. Power analyses were then applied to this relatively large dataset to assess how changes in tagged fish number influenced the individual variability in the movement metrics. Although retaining 95% of the movement variability required relatively large samples, using 60 individuals retained 90% of individual variability, with only 20 fish needed to retain 80%. These results emphasise the importance of high connectivity in wetlands to enable potadromous fish to access key functional habitats in all seasons. It also reveals relatively small sample sizes in acoustic telemetry can capture much of the movement variability measured across larger numbers of tagged fish.