Scientists probe big fish die-off

Scientists probe big fish die-off

Tests are being done in Michigan to see why thousands of dead gizzard shad are turning up along the Detroit River and in lakes Erie and St. Clair.

"The only thing we're really sure of is temperatures are likely a factor," Ministry of Natural Resources biologist Andy Cook said Thursday from Wheatley.

Gizzard shad, at the northern end of their range here, are vulnerable to the cold and has been known to have large die-offs, Cook said.

Because there seemed to be more dead fish than usual, tests are being done through the Michigan Department of Natural Resources and Environment.

Department spokeswoman Mary Dettloff said the gizzard shad found in Lake St. Clair are being tested for a deadly fish virus called VHS because some of them showed symptoms of the disease.

Viral hemorrhagic septicemia is a viral disease found in freshwater and saltwater fish in Europe, Japan and along the coasts of North America. The disease was first identified in Ontario in 2005 in Lake Ontario. Since then it has caused large die-offs of fish. It has been found in a number of species including commercial and sport fish such as walleye and yellow perch.

It is not a threat to people who eat fish.

"We might see it in other species," Dettloff said of the disease, which causes fish to bleed internally.

"We'll keep a lookout for it this spring and summer."

On Jan. 20 a Windsor resident walking his dog along the Detroit River in Alexander Park saw thousands of dead fish. The MNR found thousands of dead gizzard shad farther east near Little River on Jan. 28.

Cook said they appeared to be juvenile fish about 15 centimetres long. Gizzard shad are silver and grow to about 25 centimetres as adults. They are not an important sport fish and serve as food for larger fish such as walleye.

Expect to see more dead gizzard shad this winter and spring as the ice melts, Dettloff said. Contributing to the large die-off is the early cold weather and the fact that there are a lot of young gizzard shad this year.

The Ministry of the Environment had been called about the dead fish but is not investigating because there was no evidence pollution was the cause

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