10/03/2006

Biologists try to figure out what's killing lake birds

A naturally occurring toxin is prime suspect

BY CHRISTINE FINGER

cfinger@record-eagle.com

Record-Eagle/Douglas Tesner
Lee Bragg, a biological technician for the National Park Service, bags a dead seagull near Esch Road in Sleeping Bear Dunes National Lakeshore. A recent outbreak of Type E botulism in decaying fish has killed hundreds of fish-eating birds, including seagulls and grebes.

EMPIRE — Biologists are testing dead birds found in the Sleeping Bear Dunes National Lakeshore to determine whether they died from a toxin carried in dead fish.

Ken Hyde, a biologist at Sleeping Bear, said park employees in August sent a collection of bird species found dead along the lakeshore to the state Department of Natural Resources lab for testing. Tests came back positive for Type E botulism, a naturally occurring toxin found primarily in decaying fish.

Dead birds included seagulls, grebes and cormorants.

Hyde said it isn't unusual to see birds die of botulism when it coincides with the die-off of fish carrying the toxin. But the park has received many calls in the last week reporting dead birds along the shoreline, and there recently haven't been many dead fish.

Biologists are collecting several more species to send in for testing. Hyde predicted that test results could take several weeks.

"We're just trying to make sure it's still related to the botulism," he said.

The bacteria that causes Type E botulism is found in bottom mud, in aquatic invertebrates and in fish primarily in the Great Lakes region. Feeding invertebrates pick up the bacteria, and fish ingest the bacteria either directly from bottom mud or from eating invertebrates arising from it. Dead fish carcasses foster bacteria growth and toxin production, and birds become poisoned from feeding on the dead fish.

Hyde said the recent bird deaths could be the result of eating invertebrates churned up by lake turnover.

Judy Granger, of Empire, called park and DNR officials last week after seeing a large number of dead birds during one of her frequent walks along the lakeshore.

"It was really disturbing," she said. "The last few weeks I've just noticed so many."

Granger said she's glad biologists are running the tests, but suggested an effort to remove dead birds from the shoreline.

"I think there would have been a lot of volunteers," she said.

Hyde said Type E botulism is not generally a health risk to humans because people don't eat dead fish carcasses and thorough cooking destroys the toxin. He recommended people who find dead birds leave them alone.