Spring migratory movements by paddlefish in natural and regulated river segments of the Missouri and Yellowstone rivers, north Dakota and Montana

Paddlefish Polyodon spathula of the Yellowstone-Sakakawea stock, Missouri and Yellowstone rivers, Montana and North Dakota, were radio-tagged to assess movement patterns during spawning migrations in 1999-2002. Sixty-three of the 69 tagged fish provided useful data on migratory movements during the study period. Paddlefish exhibited repeated directional changes in movement during the spring, traveling extensively upriver and downriver in association with increasing and decreasing levels of river discharge and suspended sediment. This behavior resulted in their widespread distribution along the lower 50 kin of the Yellowstone River during late spring of all 4 years. The choice of river ascended (Missouri or Yellowstone) was also associated with increasing levels of discharge and turbidity. Paddlefish ascended the unregulated Yellowstone River rather than the regulated Missouri River more than four of every five times when moving above the confluence of the two rivers. Although paddlefish were also occasionally contacted in the Missouri River above the confluence, most forays into the Missouri River were of short duration as fish were contacted less than a week afterward in the Yellowstone River. River temperature did not play a significant role in determining directional movement or river selection. The results from this study provide insight into how annual variations in or modifications to the spring flow regime might affect movement patterns in migratory paddlefish and, consequently, spawning success.