Swimming performance of Yellowstone cutthroat trout (Oncorhynchus virginalis bouvieri)

Abstract

Yellowstone Cutthroat Trout (Oncorhynchus virginalis bouvieri) inhabit the upper portions of the Yellowstone and Snake River basins of Montana, Wyoming, and Idaho. Although individual populations remain intact in headwater streams, anthropogenic activities have resulted in substantial declines in their historic range and core population abundance, and the classification as a species of concern in Montana. To aid in Yellowstone Cutthroat Trout restoration and conservation, we conducted two studies to characterize their swimming performance. In the first study, we used an open-channel flume to observe the volitional swimming performance of 168 hatchery-raised Yellowstone Cutthroat Trout, ranging in total length from 292 to 450 mm. Fish were tested against a range of water velocities (0.61, 0.94, 1.75, and 2.00 m .s -1) and temperatures (8.0 and 12.0°C). We observed that passage success decreased with increasing water velocities, ranging from 98% at 0.61 m .s -1 to 19% at 2.00 m .s -1, and that water temperature did not affect the maximum distance of ascent within each hydraulic challenge (? 2 ranged from 0.0 to 1.0, p-value > or = 0.3, df = 1). The overall maximum sprinting velocity was 4.59 m .s -1, mean maximum swimming velocity was 2.15 m .s -1, and average water velocity at gait transitions was 0.61 m .s -1 from sustained to prolonged, 0.94 m .s -1 from prolonged to unsteady burst glide, and <1.73 m .s-1 from unsteady burst glide to steady burst. In the second study, we quantified the U sprint swimming mode of Yellowstone Cutthroat Trout using a swim chamber. Sixty fish were individually tested, which resulted in a mean U sprint velocity of 3.91 body lengths .s -1 (SD = 0.56), equivalent to 1.48 m .s -1 (SD = 0.18). U sprint values ranged from 0.86 to 1.85 m .s -1 for Yellowstone Cutthroat Trout with total lengths of 314 mm to 456 mm. Gait transitions were observed from sustained-prolonged to burst-glide swim mode at a mean water velocity of 0.88 m .s -1 (SD = 0.15) and from burst-glide to strictly burst at 1.13 m .s -1 (SD = 0.18). These findings provide valuable information for assessing passage success probability and guiding the design of fish passage structures, which are essential for the restoration and conservation of native Yellowstone Cutthroat Trout populations.