Updated: Tuesday, 11 Jan 2011, 11:51 AM CST
Published : Tuesday, 11 Jan 2011, 8:52 AM CST

Sun-Times Media Wire

Chicago - A bizarre scene is evolving on the Chicago lakefront, with Canada geese and mallard ducks gulping down dead or dying gizzard shad.

A major die-off of what appears to be the 2010 class is happening in Chicago harbors. Thousands, perhaps far more than that, of dead gizzard shad in the 3- to 5-inch range are frozen in the ice of Chicago harbors or floating around in open patches of water.

“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.

The massive die-off was first documented Thursday by Carl Vizzone, a North Side fisherman who sits on the board of Perch America. What caught his eye was Canada geese and mallards eating dying shad at open water by DuSable and Diversey harbors. “This is not normal,’’ he said.

He’s right, agreed naturalist Joel Greenberg, author of A Natural History of the Chicago Region. Canada geese and mallards normally don’t eat fish, but, Greenberg said, “They are opportunistic.”

Other species of fish do not appear to be involved in the die-off.

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.