U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2004–3038

August 2003

Upper Midwest Environmental Sciences Center, La Crosse, Wisconsin

At-Risk Riverine Fishes: Pad dle fi sh and Lake Sturgeon 

Problems

Paddlefish and lake sturgeon were common components 

of fish communities in the large rivers of the Mississippi 

River drainage before 1900. Overharvest and human 

alteration of rivers have resulted in significant declines in 

paddlefish and lake sturgeon populations. Construction 

of dams on rivers has especially affected these species by 

altering traditional river habitats and disrupting spawning 

migrations. Paddlefish have been extirpated from four 

states and Canada. Eleven of 22 states within what 

remains of its range now list the paddlefish as endangered, 

threatened, or a species of special concern. Similarly, 

lake sturgeon is listed as a species of special concern 

throughout most of its native range. 

We captured lake sturgeon and paddlefish with gill and hoop nets for 

the telemetry studies.

Center scientists tracked radio-tagged paddlefish in the Upper 

Mississippi River.

Aerial photo of Lock and Dam 5 near Winona, Minnesota. The locks and 

dams on the Upper Mississippi River can impede upstream movements 

of these large fishes.

Solutions

Restoration efforts for these species require knowledge 

of the factors that are negatively affecting their 

populations. To identify these factors, the Upper Midwest 

Environmental Sciences Center, in collaboration with 

the U.S. Fish and Wildlife Service, conducted telemetry 

studies in which we surgically implanted radio transmitters 

into captured fish in the Mississippi, Wisconsin, and 

Chippewa Rivers. Then we tracked individual paddlefish 

and lake sturgeon to determine important features and 

availability of their habitats, delineate the appropriate

scales for managing stocks, assess the role of dams in 

impeding migrations and fragmenting populations, and 

evaluate fish responses to commercial traffic. These 

telemetry studies provide substantial new insights into 

the effects of navigation and river modifications on these 

special species.
Center biologist measures dissolved oxygen at a fish location.

Research Findings to Date

Lake Sturgeon

• Individual lake sturgeon are often found in small, 

core areas that contain silt or silt-sand substrates 

and moderate flow. These areas likely provide high 

densities of common prey of lake sturgeon.

• Lake sturgeon are highly mobile. Individual lake 

sturgeon occasionally leave their core area with 

movements up to 120 miles, but generally return after 

being absent for a few weeks to months. 

• Lake sturgeon tagged in the Upper Mississippi 

River made extensive use of the Wisconsin River, 

a tributary to Pool 10 south of Prairie du Chien, 

Wisconsin. This indicates that the population 

transcends regulatory boundaries. For example, two 

female lake sturgeon with eggs were tagged in 

Pool 10 where they are protected, but were later 

harvested in the Wisconsin River during the fall 

fishing season.

• Lake sturgeon extensively use main channel and 

channel border areas in the Upper Mississippi 

River, indicating a high potential for encounters 

between lake sturgeon and commercial barge 

traffic. Individual lake sturgeon respond 

differently to barge passage; some appear to be 

forced out of the main channel, whereas others 

remain in the main channel, risking being struck 

by towboat propellers. 

Paddlefish

• Paddlefish in the Upper Mississippi, Chippewa, 

and Wisconsin Rivers may be a single genetic 

stock given that that some individual paddlefish 

moved between all of these rivers.

• The paddlefish population in the Chippewa River 

is strongly connected to the main stem of the 

Mississippi River (50% or more of the tagged fish 

each year spend at least one month in the Mississippi 

River), whereas Wisconsin River paddlefish rarely 

enter the Mississippi River. 

• The low-head navigation dams in the Upper 

Mississippi River appear to function as intermittent 

barriers to paddlefish movement. Upstream passage 

of fish through dams typically occurs only during 

floods when dam gates are completely raised out of 

the water.

• Our study shows that areas with a combination of 

low flow velocities and deep water (usually deeper 

than 6 m) are important habitat for paddlefish in the 

Upper Mississippi River. Such habitat is susceptible 

to sedimentation and may be in decline. 

Center scientists hold a paddlefish captured and released in the study.

For more information, contact

USGS Upper Midwest Environmental 

Sciences Center

2106 Fanta Reed Road

La Crosse, WI 54603

Brent Knights

608.781.6332

bknights@usgs.gov

Steve Zigler

608.781.6395

szigler@usgs.gov

http://www.umesc.usgs.gov