We used passive egg collectors during May, June, and July of2003 and 2004 in the lower 50 river kiiometers (rkm) of the Yellowstone River, eastern Montana and western North Dakota, to detect egg deposition by spawning paddle fish (Polyodon spathula). Sampling yielded 292 eggs (46 in 2003 and 246 in 2004). All egg collections in 2003 occurred on the descending limb of the spring hydrograph but 99% of egg collections in 2004 occurred before the spring hydrograph began to descend. Catch-per-unit-effort (CPUE) in 2004 was about four times that of 2003. A combination of river conditions, in addition to rising or falling discharge levels, might have influenced the difference in timing of egg deposition between years. Water temperatures at time of peak egg CPUE were near 17.0°C in both years; however discharge and sediment levels were different. Although our study did not attempt to describe the entire spatial range of egg deposition, more eggs were found in lower reaches (rkm 13.7 and rkm 26.5) than in upper reaches (rkm 37.0 and rkm 40.2) of similar habitat character. The presence of adequate spawning substrate in the lower 27 rkm of the Yellowstone River might encourage egg deposition and successful paddlefish spawning if annual spring flood-pulses persist
