When you think of migrating fish, usually silvery salmon gracefully leaping up waterfalls in the Pacific Northwest come to mind. In fact, many freshwater fish migrate in order to spawn, even the small minnows and chubs of the large, muddy rivers of the Great Plains. These large rivers are now interrupted by numerous dams, diversion structures, and dewatered channels, which are thought to be a key factor in the decline of many plains fish species. But how do you prove that a small fish in a muddy river actually migrates? In a recent article in the Transactions of the American Fisheries Society, a team of scientists from the U.S. Geological Survey and Colorado Parks and Wildlife attempted to see if an imperiled species, the Flathead Chub, migrates upstream to spawn in Fountain Creek, Colorado. The outcome would influence the construction of a fishway at the diversion dam farthest downstream on the creek. More than 10,000 chub were captured at various sites along the creek, marked, and released. During the summer spawning season, five times as many chub were found at the bottom of the dam than at other sites along the river. Of more than 6,000 fish captured and marked at the dam site, only 10 were recaptured upstream of the dam. Because this diversion structure is the obstacle farthest downstream of the 29 potential barriers on Fountain Creek, the authors note that a fishway there will produce the greatest benefits for Flathead Chub.
Barriers Impede Upstream Migration of Flathead Chub, by David M. Walters, Robert E. Zuellig, Harry J. Crockett, James F. Bruce, Paul M. Lukacs, and Ryan M. Fitzpatrick. Transactions of the American Fisheries Society 143:17-25.