Diversity of behavioural patterns displayed by a summer feeding aggregation of Atlantic sturgeon in the intertidal region of Minas Basin, Bay of Fundy, Canada

Quantifying animal movements can reveal spatial and temporal patterns of habitat use and may improve our understanding of the foraging strategies of marine predators where direct observations of feeding behaviour are rare or impossible because of turbidity. Fine-scale movement data from 25 acoustically tagged Atlantic sturgeon Acipenser oxyrinchus (Mitchill, 1815) were gathered using a Vemco Positioning System array of hydroacoustic receivers in the intertidal zone of Minas Basin, Bay of Fundy, Canada, during summer 2011. From these data, sturgeon relocations and movement trajectories were determined. Sturgeon movement trajectories were categorized into 3 movement types by analyzing 4 calculated metric variables including (1) mean distance between successive relocations; (2) mean relative angle or 'turning angle'; (3) mean rate of movement (ROM; m s(-1)); and (4) a linearity ratio. Movement Type 1 trajectories were characteristically slow and winding, with short steps between relocation, whereas Type 2 movements were fast and tortuous. Movement Type 3 trajectories were fast and linear, with large steps between relocations. Considerable variability in movement type was recognized with 11 individuals performing all 3 types of movement during the monitoring period. Movement Types 1 and 2 occurred primarily over the intertidal zone, where sediment type was comprised of larger sand and sandy/silt particles. This association with larger grain size may coincide with a diet preference for sand-tube dwelling polychaetes and indicates the importance of the intertidal zone to foraging Atlantic sturgeon. All movement types were equally likely to occur throughout a 24 h day and throughout all tidal stages; however, there was higher overall crepuscular activity which revealed a temporal pattern not previously recognized for Atlantic sturgeon.