Contacts
Jim Nissen,
La Crosse District (608) 783-8401
Scott Flaherty
612-713-5309
Intestinal
parasites, known as trematodes or flukes, are believed to be the cause of
a large scale die-off of lesser scaup, coots, and ring-necked ducks on Lake
Onalaska and along the main channel of the Upper Mississippi River immediately
below Lock and Dam 7 near Dresbach, Minn. Refuge staff at the La Crosse District
of the Upper Mississippi River National Wildlife and Fish Refuge have observed
large numbers of the sick and dead water birds and say higher river flows
are moving some of them through the dam and depositing them along the main
channel in the upper part of Pool 8.
Trematode-caused
waterfowl and coot mortality has been documented each spring and fall on
Lake Onalaska since the 2002 spring migration. During the 2004 spring migration,
about 1,060 sick/dead birds were found and total mortality was estimated
at 2,400 to 2,700. Comparable losses occurred during the 2004 fall migration.
Mortality this spring was first observed on March 28 and is expected to continue
through the end of April.
Carcasses
are being shipped to the U.S. Geological Survey’s National Wildlife
Health Center in Madison, Wis. for examination.
Most trematodes
have complex life cycles that require two intermediate hosts in which the
parasites develop before they become infective for the definitive, final
bird host. At least two different species of trematodes have been found in
the digestive tracts of birds involved in past die-offs. Both species are
small, ranging in size from 1 millimeter to less than 2 millimeters.
Last summer
and early fall, parasitologists from the National Wildlife Health Center
and Minnesota State University at Mankato, Minn. sampled snails in selected
areas of Lake Onalaska. Among the findings, an exotic snail, known as the
faucet snail (Bithynia tentaculata), is now present in the river and serves
as the first and second intermediate host for both species of trematodes.
A portion of the snails collected and examined from various sites on Lake
Onalaska were infected with the trematodes.
Based on a
review of the literature, this snail appears to be a newcomer to the Upper
Mississippi River. Native to Europe, faucet snails were first found in Wisconsin
in the Great Lakes basin in the early 1900’s. In 1998, these snails
were documented in Shawano Lake. Die-offs of coots and lesser scaup from
trematodes closely parallel locations within Wisconsin where faucet snails
have been found.
Depending
on how heavily snail populations are infected, some birds can receive a lethal
dose during less than 24 hours of feeding. Susceptible waterfowl can die
3-8 days after ingesting a lethal dose of the trematodes.
Avian predators
and scavengers, such as bald eagles, crows, and gulls, have been feeding
on the sick/dead birds. Mammals, such as raccoons and coyotes, may also be
feeding on the carcasses. According to Wildlife Disease Specialists, there
appears to be no documented threat that raptors or scavengers feeding on
infected carcasses are at risk.
For more information,
or to report finding sick or dead waterfowl or coots in areas other than
Lake Onalaska, contact the La Crosse District Office of the U.S. Fish and
Wildlife Service at 608-783-8405.
The U.S. Fish
and Wildlife Service is the principal federal agency responsible for conserving,
protecting and enhancing fish, wildlife and plants and their habitats for
the continuing benefit of the American people. The Service manages the 95-million-acre
National Wildlife Refuge System, which encompasses 545 national wildlife
refuges, thousands of small wetlands and other special management areas.
It also operates 69 national fish hatcheries, 63 Fish and Wildlife Management
offices and 81 ecological services field stations. The agency enforces federal
wildlife laws, administers the Endangered Species Act, manages migratory
bird populations, restores nationally significant fisheries, conserves and
restores wildlife habitat such as wetlands, and helps foreign governments
with their conservation efforts. It also oversees the Federal Assistance
program, which distributes hundreds of millions of dollars in excise taxes
on fishing and hunting equipment to state fish and wildlife agencies.
-FWS-
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