Scaphirhynchus Conference: Alabama, Pallid, and Shovelnose Sturgeon

St. Louis, Missouri, 11-13 January 2005

37.  RIVER CONNECTIVITY FOR MIGRATING SHOVELNOSE STURGEON IN THE LOWER PLATTE RIVER, NEBRASKA.

James E. Parham*, 311 Biochemistry Hall, School of Natural Resources, University of Nebraska, Lincoln, NE 68583-0759; Phone 402-472-2931; FAX 402-472-8390; jparham2@unl.edu

Benjamin D. Swigle, 6935 Washburn Way, Klamath Falls Biological Field Station, USGS, Klamath Falls, OR, 97603; Phone 541-273-8689; bswigle@usgs.gov

Edward J. Peters, 12 Plant Industry, School of Natural Resources, University of Nebraska, Lincoln, NE, 68583-0814; Phone 402-472-6824; epeters2@unl.edu

The lower Platte River, a large Missouri River tributary, still exhibits the shallow shifting sandbar morphology characteristic of much of the predevelopment Missouri River. While the lower Platte River has no manmade barriers to restrict sturgeon movement, declines in discharge change a swiftly flowing open water channel to a maze of exposed and shallow sandbars. To assess the role of discharge on the river connectivity and, therefore, the ability of sturgeon to migrate within the river, instream habitat was classified from aerial images for 29 sections of the lower Platte River. Habitat was classified into one of four categories: open water, shallow sandbar complexes, exposed sand, or woody islands.  A total of 246 km of river from 3 different years were classified with sections averaging 8.2 km long. Discharge for each section was recorded as the average daily discharge from the nearest appropriate USGS gage location. Twenty different discharges were recorded, varying with the location and date of the image, and ranged from 0 cms to 595 cms. Connectivity within a section was recorded as the longest continuous section of open water with at least 25 m width. The relationship between river connectivity and river discharge was found to be a nonlinear where the river was relatively unconnected at low discharge, and rapidly changed to fully connected at moderate discharge levels. Results from the river connectivity relationship were compared to movement patterns of 19 radio-tagged shovelnose sturgeon. Sturgeon movement correlated with river connectivity and water temperature as, on average, most of the lower Platte River was connected during the spring upstream and early summer downstream migrations. During periods of low connectivity, sturgeon displayed little directed movement. Results from this study will be used to assess current Platte River instream flow standards to ensure sturgeon have a passageway during their migratory period.