8094 - Laserfiche WebLink

Home Browse Search

Pallid sturgeon evolved in the diverse environments of the Missouri and Mississippi Rivers. Floodplains, backwaters, chutes, sloughs, islands, sandbars, and main channel waters formed the large-river ecosystem that provided macrohabitat requirements for pallid sturgeon and other native large- river fish, such as paddlefish and other sturgeon. These habitats were historically in a constant state of change. Today these habitats and much of the once naturally functioning ecosystem has been changed by human developments. The historic floodplain habitat of the Missouri and Mississippi Rivers provided important functions for the native large-river fish. Floodplains were the major source of organic matter, sediments, and woody debris for the main stem rivers when floodflows crested the river's banks. The transition zone between the vegetated floodplain and the main channel included habitats with varied depths described as chutes, sloughs, or side channels. The chutes or sloughs between the islands and shore were shallower and had less current than the main channel. These areas provided valuable diversity to the fish habitat and probably served as nursery and feeding areas for many aquatic species (Funk and Robinson 1974}. The still waters in this transition zone allowed organic matter accumulations, important to macroinvertebrate production. Both shovelnose sturgeon and pallid sturgeon have a high incidence of aquatic invertebrates in their diet (Carlson et al. 1985; Gardner and Stewart 1987). Floodflows connected these important habitats and allowed fish from the main channel to utilize these habitat areas and to exploit available food sources. Floodflows also stimulated spawning migrations. Before impoundment behind reservoirs, there were two periods of peak discharge on ,the Missouri River; one in-April resulting from spring runoff and snowmelt on the Great Plains and a second higher peak in late May to early June resulting from mountain snowmelt. Both shovelnose sturgeon and paddlefish spawning migrations occur in response to increased flows in June (Berg 1981). Although there is no information on pallid sturgeon spawning ,migrations, it is assumed these migrations would similarly occur in response to increased, June flows. Micro-habitat characteristics of pallid sturgeon are just recently being described. Much of the micro-habitat research to date has been a characterization of habitat where pallid sturgeon are. being located in the significantly altered environments of today. This research does not necessarily indicate preferred or required habitats; instead it may only indicate which habitats of those presently available are used by the pallid sturgeon. Also capture locations may have conditions representing seasonal habitat preferences. Current Velocity: Preliminary findings from a study on the Missouri River in South Dakota indicate that pallid sturgeon most frequently occupy river bottoms where velocity ranges from 10 to 30 centimeters per second (cps) (0.33 to 0.98 feet/sec), (J. Erickson, South Dakota State University, pers. comm. 1992). Studies on microhabitat selection of pallid sturgeon in Montana found that they are most frequently associated with water velocity ranging from 40 to 90 ,cps (1:3 to 2.9 feet/sec)., (P. Clancey, Montana Dept. of Fish, Wildlife, 7