DOWNTOWN — The largest fish swimming in Chicago waters predate some dinosaurs.
There are a small number of lake sturgeon still inhabiting Lake Michigan off the city's lakeshore, according to Phil Willink, senior research biologist at Shedd Aquarium. Although the last officially recorded lake sturgeon to be recorded in Chicago was five years ago this month — when one was found in a water pipe in Lake Michigan — there are others in city waters, Willink said.
"They're more common to the north in Michigan and Wisconsin, but there are strays swimming along the lakeshore here," Willink said. "The dinosaurs are gone, but the sturgeon are still here."
That includes the fish, which can grow to 9 feet long and weigh up to 300 pounds, in Lake Michigan and possibly in Wolf Lake on the Southeast Side. A sturgeon was caught in Wolf Lake in 2009, Willink said, but it's unclear how it got there. The fish was originally tagged in Wisconsin, and it could have swum from Lake Michigan through a tributary into Wolf Lake, or a person could have transported it into Wolf Lake, Willink said.
Lake sturgeon have a special place in the city's history. In the book "A Natural History of the Chicago Region," the fish, which thrived more than 100 million years ago during the Cretacuous Period, also were found in huge numbers in Chicago until the late 1800s.
They were found in the Calumet River, Lake Calumet and Wolf Lake, but suffered huge population declines due to overfishing. A giant sturgeon, as much as 240 pounds, was caught in Lake Michigan near Rogers Park in 1906.
Sturgeons, which have bony plates in their skin, are older than some dinosaurs, which reigned between 65 million and 230 million years ago. Some sturgeon fossils have been found inside dinosaur fossils, Willink said.
They are bottom feeders, dining on worms, aquatic insects, mussels, crayfish and even amphibians, Willink said. They can live upward of 150 years, he said.
Sturgeon have been released recently in Michigan waters, but it's unlikely they'll be reintroduced in city waterways anytime soon, Willink said. Sturgeon need fast-running water that moves over rocks to spawn, and Chicago's slow-moving rivers don't provide that, he said.
Although there are limited fishing seasons for sturgeon in Michigan and Wisconsin, it's illegal to fish for them here because they're endangered in Illinois, Willink said.
Willink said he believes most Chicagoans would be shocked that there are even a few sturgeon swimming in city limits.
"They have no idea there are fish that big in Lake Michigan," he said.
The Shedd Aquarium has a "touch pool" filled with sturgeon, where visitors can touch the fish.
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