Abstract
Five native fish species, Pallid Sturgeon Scaphirhynchus albus , Shovelnose Sturgeon Scaphirhynchus platorynchus , Paddlefish Polyodon spathula , Blue Sucker Cycleptus elongatus , and Sauger Sander canadensis , were evaluated with radio telemetry over the period 2015–2018 for their ability to pass Intake Dam, a low‐head irrigation diversion dam on the Lower Yellowstone River, Montana, and ascend upriver. The objectives were to (1) quantify frequency and timing of passage success of the five species past Intake Dam; (2) document the choice of passage route past the dam (i.e., over the dam or via a natural side‐channel); (3) quantify the extent of upriver movement of fish passing the dam; and (4) interpret species results and differences by synthesizing and reviewing relevant key migration, hydraulic, and ecomorphological studies on these species. All species used both routes (over the dam and the side channel) for upriver passage, but passage success differed greatly among species. Overall upriver passage of Acipenseriform species (sturgeons and Paddlefish) encountering the dam did not exceed 20% over the 4‐year study via the two combined possible routes; annual passage rates never exceeded 28.6%. Pallid Sturgeon and Paddlefish primarily used the side‐channel. In contrast, the passage rates of Blue Sucker (97.9%) and Sauger (63.3%) encountering the dam were much higher. Blue Sucker almost exclusively passed over the dam; Sauger passage was split between over the dam (42%) and via the side‐channel (58%). Multiple (post hoc) comparisons indicated that Yearling Pallid Sturgeon passage success at the dam was significantly lower than other groups of Pallid Sturgeon (i.e., hatchery‐reared and wild) as well as all other species. In contrast, Blue Sucker and Sauger passage success was significantly higher than the other species, with Blue Sucker passage success significantly higher than Sauger. Once fish from all five species passed the dam, all fish moved more freely than when below the dam, and passage of fish encountering Gibbs Station, an unimpeded control reach boundary upriver, ranged from 67% to 100% depending on species. Whereas upriver passage past the dam incorporated the two routes, all the downriver passage to below the dam occurred over the dam. The differences among species in their ability to pass the dam, in their passage route (over the dam or side channel) and passage through an unobstructed upriver control reach were related to discharge magnitude, timing, and duration, as well as to life history, ecomorphological, and behavioral differences among species documented in other studies.