Chicago Fish Die-Off: Thousands Of Shad Dead In Lake Michigan

In another in a bizarre series of international animal die-offs, thousands of gizzard shad have been turning up dead along the Chicago lakefront in recent days.

The three- to five-inch fish, members of the herring family, were dying in droves, frozen in chunks of ice or simply going belly-up in open water.

The fish die-off has turned the local ecosystem somewhat topsy-turvy, as Canada geese and mallards have been swooping in to the cold Lake Michigan waters to prey on the dead shad.

The birds don't ordinarily eat fish at all, but naturalist Joel Greenberg told the Chicago Sun-Times that they're "opportunistic."

More from the Sun-Times, on the possible cause:

"Gizzard shad are pretty sensitive," Lake Michigan Program biologist Dan Makauskas said. "On the toughness scale, the herrings are pretty soft."

Gizzard shad, members of the herring family, are more sensitive to drops in oxygen levels than most fish. And thick ice came early to Chicago harbors in December.

Makauskas, who speculated that the young shad may not have built up enough reserves to survive the early onslaught of extreme cold, agreed the die-off is abnormal.

The incident follows on the heels of dozens of bizarre die-offs around the country and the world. Dead birds fell from the sky in Arkansas, Louisiana, Kentucky, California, Italy and Sweden in recent weeks; two million dead fish washed up in the Chesapeake Bay, while 100 tons of dead fish hit the shores in Brazil and 40,000 dead crabs turned up on English beaches.

Naturalists suggest that the massive animal deaths are unrelated, and offer explanations from sudden temperature drops to fireworks explosions to account for the individual incidents.