East Channel: Prairie du Chien
Crawford County, Wisconsin
“In the Upper Mississippi, half-buried in silt and sand, are scattered congregations of naiad mussels. They are simple creatures, little more than two strong shells or ‘valves’ enclosing a soft, formless body. Blind and virtually brainless, they lie on the river bottom with shells agape, laved in the currents that bring them food and oxygen.”–John Madson, 1985
First, John Madson loved the Upper Mississippi River. His book, Up On the River, describes the history of the river, the critters who live in the river, and the characters who fish the river. If you love the Mississippi, find this book.
Second, hypoxia, which creates the Dead Zone in the Gulf of Mexico, is also a problem on the Upper Mississippi River, where 26 locks and dams have created 26 lakes. Hence, nutrients, washed into the river from upland farms, get trapped behind the dams and create low-oxygen conditions or hypoxia.
At Prairie du Chien, Wisconsin the Mississippi breaks into two channels, separated by Island #172. Of the forty-four species of mussels that live along the Upper Mississippi, the East Channel was once home to thirty. Between 1995 and 1999 the number of species in East Channel declined to seven, with a loss of ninety-eight percent of the population. They lost habitat to the zebra mussel, an exotic species carried from Asia in the ballast of ships.
The zebra mussel does a fine job of filtering the water, clearing the river of sediment, and improving the habitat for game fish, but it has paved over native mussel beds. In the summer of 2000, divers, searching for the endangered Higgins Eye, had to work their arms down through layers of zebra mussels clear to their shoulders before reaching the riverbed.
The mussel they were searching is three to four inches in diameter. Its habitat on the Upper Mississippi ranges from Prescott, Wisconsin south to Iowa and Illinois, and in the Wisconsin and St. Croix rivers. Its shells are golden-olive brown with dark rings and green and orangish rays. The lining of the calcium shell is an iridescent white or pink mother of pearl. The soft animal inside has a single foot, which pushes its shell along the muddy bottom of the large rivers it inhabits. Over the course of a thirty-year life span it travels no more than a few hundred yards.
When it is young and tiny, small fishes, water birds, and other predators feed on it. When it is fully grown, muskrats, raccoons, and other fur bears feed on it, as well as waterfowl and large fishes. The Higgins Eye anchors itself, slightly open, in the sand and gravel substrate in the swift current along the main channel of the river or in a fast-flowing side channel like East Channel. Like the zebra it filters its food through its body, taking in microorganisms and water through one siphon and releasing waste through a second. Along with food, the Higgins Eye takes in toxins and sediment suspended in the water. Silt, washing down from upland farms, can bury mussel beds. Nutrients, washing into the Mississippi from upland farms, can fertilize algae, which absorbs the oxygen from the water and creates a low-oxygen environment, not healthy for creature which cannot come to the surface to breath. Therefore, the health of the Higgins Eye and other mussels is a measure of the health of a body of water. All of these conditions, low-oxygen water, toxins in the water, silt smothering mussel beds, the zebra mussel can lead to the loss of mussel communities before they effect larger fish communities. Hence, the Higgins Eye is endangered and disappearing from the nation’s rivers.
Upriver from East Channel, the Genoa National Fish Hatchery began propagating the Higgins Eye mussel in 1999, releasing 1.1 million mussels into the Upper Mississippi in the first four years of the project. Mussels reproduce through a complex process. The male releases sperm into the water. The female draws them in through her siphons and into her gills where her eggs are held and fertilized. She holds the fertilized eggs in the gills for several weeks or months, until they mature into larvae call “glochidia.” Then she releases them into the water, where they must take up residence in the gills of a host fish, metamorphose into a juvenile mussel, and are released from the host into the river.
Madsen, Up on the River, 63; Wisconsin Department of Nataural Resources, “Higgins’ Eye Pearly Mussel,” http://www.dnr.state.wi.us/org/land/er/factsheets/mussels/HPEMUSSL.HTM: U.S.Fish and Wildlife Service, Genoa National Fish Hatchery, “Endangered Mussel Recovery,” http://www.fws.gov/midwest/Genoa/musssel_recovery.html.
Filed under: Dead Zone, Fine Art Photography, Mississippi River, Mussels, Photography, Upper Mississippi, Water Quality, Zebra Mussel | Tagged: East Channel, Higgens Eye Mussel, Hypoxia, Island #172, low-oxygen water, Mississippi River, photograph, Prairie du Chien |