Many lotic fish species use natural patterns of variation in discharge and temperature as spawning cues, and these natural patterns are often altered by river regulation. The effects of spring discharge and water temperature variation on the spawning of shovelnose sturgeon Scaphirhynchus platorynchus have not been well documented. From 2006 through 2009, we had the opportunity to study the effects of experimental discharge levels on shovelnose sturgeon spawning in the lower Marias River, a regulated tributary to the Missouri River in Montana. In 2006, shovelnose sturgeon spawned in the Marias River in conjunction with the ascending, peak (134 m 3 /s) and descending portions of the spring hydrograph and water temperatures from 16 C to 19 C. In 2008, shovelnose sturgeon spawned in conjunction with the peak (118 m 3 /s) and descending portions of the spring hydrograph and during a prolonged period of increased discharge (28-39 m 3 /s), coupled with water temperatures from 11 C to 23 C in the lower Marias River. No evidence of shovelnose sturgeon spawning was documented in the lower Marias River in 2007 or 2009 when discharge remained low (14 and 20 m 3 /s) despite water temperatures suitable and optimal (12 CÀ24 C) for shovelnose sturgeon embryo development. A similar relationship between shovelnose sturgeon spawning and discharge was observed in the Teton River. These data suggest that discharge must reach a threshold level (28 m 3 /s) and should be coupled with water temperatures suitable (12 CÀ24 C) or optimal (16 CÀ20 C) for shovelnose sturgeon embryo development to provide a spawning cue for shovelnose sturgeon in the lower Marias River.

Mountain Whitefish Prosopium williamsoni is a native salmonid distributed throughout the Columbia River basin, but little is known about the life history traits of tributary-specific populations. We captured and tagged 129 Mountain Whitefish with passive integrated transponder (PIT) tags between 2010 and 2015 at a weir on the Twisp River, Washington, to assess migration patterns. Detection records suggested that two populations of Mountain Whitefish overlap in the Twisp River during spring: resident fish that spawn in the Twisp River (42% of fish) and migrant fish that spawn in the Okanogan River (58% of fish). The median entry day into the Twisp River was similar for resident (April 17) and migrant (April 16) populations, but median exit day was significantly earlier for migrant (July 2) than for resident fish (November 6). Migrant fish exited the Methow basin and traveled at 14.1 river kilometers per day, passing the lower Okanogan River PIT antenna with a median date of September 17. After spawning and overwintering in the Okanogan River with a median exit date of March 16, these fish returned to the Methow basin traveling at 22.1 river kilometers per day. These results improve our understanding of Mountain Whitefish life history and habitat use in tributaries upstream of Wells Dam, Washington.