Scaup die-off

On the heels of my last post, about the "Scaup Tracker", both Kathy Mock and Paula Lozano forwarded on a rather alarming article from the Duluth Tribune about a significant incidence of scaup mortality. Read on:

Thousands of bluebills dead since Thursday
Sam Cook, Duluth News Tribune - 11/06/2007

Dan Markham and Noel Hill of Duluth were setting up to hunt ducks on Lake Winnibigoshish near Deer River on Saturday when they noticed a dead bluebill on shore. A quick walk along the shore turned up another three dozen dead bluebills.

Waterfowl biologists with the Minnesota Department of Natural Resources estimate that as many as 3,000 bluebills, also known as lesser scaup, may have died along the west shore of Lake Winnie.

The die-off began Thursday, said Steve Cordts, DNR waterfowl specialist in Bemidji. Biologists believe the cause is a microscopic trematode, a kind of fluke, present in snails that the bluebills are feeding on.

Cordts thinks the die-off could continue. “We’re going to find a lot more dead,” he said in a telephone interview Monday.

Cordts and other DNR employees collected about 1,000 dead bluebills from a stretch of shoreline on Friday. In the time it took to collect about 900 of those birds, another 30 to 50 had died in the same stretch.

“This is potentially pretty bad because of this snail,” Cordts said. “The trematode is likely brand new to the system. It could be along the whole stretch of the Mississippi River and could get into other lakes and into other species. It’s way too early to speculate a lot.”
“We were just heartbroken,” Markham said. “It’s depressing.”

The die-off also has affected coots, Cordts said, although most coots have already left Lake Winnie. He didn’t know how many bluebills remained on the lake.

The snail that apparently is a host of the trematode is the banded mystery snail, Cordts said. It was first documented on Lake Winnie eight years ago by fisheries biologists.
“It’s been concentrated on the west side [of the lake],” he said. “Its numbers have really exploded.”

Die-offs of waterfowl due to trematodes have occurred in the spring and fall since about 2002 on the Mississippi River near Winona, Minn., Cordts said, though not in numbers as high as those on Lake Winnie.

DNR officials sent a few ducks to the National Wildlife Health Center in Madison, Wis., on Thursday. An initial inspection turned up the trematode identification in one duck, but DNR officials were waiting Monday for confirmation of that in other samples.

Hunters or others should not eat any duck that appears to be obviously diseased, Cordts said. Hunters should use latex gloves when cleaning their ducks.

Cordts said he doesn’t know of any other major waterfowl die-offs due to trematodes other than those near Winona. Controlling the snail that serves as a host would be “almost impossible,” he said.