Historical Changes in Large River Fish Assemblages of the Americas
Changes in Fish Assemblage Structure of the Red River of the North
Luther P. Aadland, Todd M. Koel, William G. Franzin, Kenneth W. Stewart, and Patrick Nelson
Abstract.—The Red River of the North basin (RRNB) has an area of about 287,000 square kilometers of the upper Midwestern United States and south-central Canada. The river forms the North Dakota–Minnesota boundary and flows into Lake Winnipeg, Manitoba, and then, via the Nelson River, into Hudson Bay. While the Red River main stem remains a sinuous stream similar to early descriptions, the river’s watershed has been altered dramatically by intensive agriculture, wetland drainage, channelization of tributary streams, and dam construction. Early land surveys described a landscape largely covered by prairie and wetlands. However, thousands of kilometers of ditches have been excavated to drain wetlands for agriculture in the United States in the late 1800s to the 1920s, and continuing, in Canada, to the present. Over 500 dams have blocked access to critical spawning habitat in the basin starting in the late 1800s. Also, during the mid-1900s, many of the tributaries were channelized, causing the loss of several thousand stream kilometers. While much of RRNB’s fish assemblage remains similar to earliest historical records, the loss of the lake sturgeon Acipenser fulvescens is a notable change resulting from habitat loss and fragmentation, and overfishing. Additional localized extirpations of channel catfish Ictalurus punctatus, several redhorse Moxostoma species, sauger Sander canadensis, and other migratory fishes have occurred upstream of dams on several tributaries. Presently, efforts are underway to restore migratory pathways through dam removal, conversion of dams to rapids, and construction of nature-like fishways. Concurrently, lake sturgeon is being reintroduced in the hope that restored access to historic spawning areas will allow reestablishment of the species. Proposed construction of new flood control dams may undermine these efforts.