Movement of Scaphirhynchus species in the Missouri River above Fort Peck Reservoir, Montana
Richards, Ryan Roy
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Some Scaphirhynchus spp. populations are endangered, in decline or extirpated. Operation of dams and reservoirs on the Missouri River has been implicated in declines in Scaphirhynchus spp. abundance. It is hypothesized that discharge from dams upstream of Scaphirhynchus spp. populations are insufficient to provide the environmental cue initiating spawning migrations. The goal of this thesis was to investigate the effects of variations in spring discharge on movements of Scaphirhynchus spp. in the Missouri River above Fort Peck Reservoir. A secondary goal was to provide information on the distribution of Scaphirhynchus spp. locations relative to larval drift distance. Twenty-four hatchery-reared juvenile pallid sturgeon, seven adult pallid sturgeon, and 192 shovelnose sturgeon were tracked from 2006 through 2009 and movements were compared among years with hydrologic conditions from above to below average discharge. Seventy-eight shovelnose sturgeon in five reproductive categories (i.e., males, confirmed spawning females, potentially spawning females, atretic females, and reproductively inactive females) were tracked in 2008 and 2009. Movements were compared among all reproductive categories within years and between years for confirmed spawning females while integrating the environmental effects of discharge and water temperature. The majority of pallid sturgeon locations in all years were within 75 km of the headwaters of Fort Peck Reservoir. Shovelnose sturgeon locations were distributed across the entire study reach, and were 100 km further upstream than pallid sturgeon locations. Based on current estimates, an insufficient length of river exists upstream of the Fort Peck Reservoir headwaters for pallid sturgeon larval drift. Movement rates of Scaphirhynchus spp. did not differ among years 2006-2009, and movements did not differ between years for confirmed spawning female shovelnose sturgeon 2008-2009, indicating that discharge did not influence movements. At the conditions in this study, movement rates of confirmed spawning female shovelnose sturgeon were highest at water temperatures suitable for spawning regardless of discharge, providing support for the hypothesis that water temperature rather than discharge is a more likely proximate cue initiating spawning migrations in Scaphirhynchus spp.