The swimming performance and associated swimming behaviour (i.e. substratum-skimming, station-holding and free swimming) were assessed in shortnose sturgeon Acipenser brevirostrum during critical swimming and endurance swimming tests over a rough and a smooth substratum. It was hypothesized that the addition of a rough substratum in the swimming flume may provide a surface for the A. brevirostrum to grip and offer an energetic advantage. Substratum type did not affect the critical swimming performance, but A. brevirostrum consistently performed more bottom behaviours (i.e. substratum-skimming and station-holding) while on a smooth substratum. Acipenser brevirostrum had little contact with the rough substratum until the velocity was >1 body length s . Endurance swimming time was significantly lower for A. brevirostrum over the rough bottom at the highest velocity (30 cm s ) which may be attributed to the observed increase in free swimming and decrease in bottom behaviours. During endurance swimming, the rough substratum was mainly used at intermediate velocities, suggesting that there may be a stability cost associated with being in contact with the rough substratum at certain velocities.

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Previous results show that juvenile shortnose sturgeon are steady swimmers and, compared with salmonids, generally have low critical swimming (UCrit) and endurance swimming capacities. Most studies on swimming capacities of sturgeon, and other fishes, include those where fish have only been swum once and the metrics of swimming performance are assessed (e.g., time swum, speed achieved). Under natural conditions, there are ample instances where fish undergo multiple swimming cycles when traversing fish ways, culverts and other sources of fast water flow. While some evidence exists for salmonids, the effects of repeat swimming are not well known for sturgeon. The current study consisted of two experiments. The first examined the UCrit of juvenile shortnose sturgeon following three consecutive swimming trials with a 30 min recovery period between subsequent tests. The second examined the endurance swimming capacities of juvenile shortnose sturgeon following three consecutive swimming trials with a 60 min recovery period between subsequent tests. Our findings indicate that (i) UCrit was consistent (~2 body lengths/s) among swimming trials; (ii) significant individual variation exists between individuals in the endurance swimming trials; and (iii) consistent results exist for individuals across swimming trials in both the UCrit and the endurance swimming tests. These results suggest that juvenile shortnose sturgeon have a high recovery capacity, and their behaviour and morphology likely reflect aspects of their swimming capacities.