Fish Fry Day: Ancient Fish, Windy City

Spotted gar found for first time in the North Shore Channel CAWS, with IDNR fisheries biologist Frank Jakubicek. Photo courtesy of: IDNR
Spotted gar found for first time in the North Shore Channel CAWS, with IDNR fisheries biologist Frank Jakubicek.
Photo courtesy of: IDNR

Last month, Illinois Department of Natural Resources fisheries biologists on a routine patrol of the North Shore Channel, a straight as an arrow, concrete-lined tributary of the Chicago River, made a surprising find. They gave the water a jolt with their electrofishing equipment and, there, north of downtown Chicago and right downstream from a Red Lobster and Olive Garden, a spotted gar rose to the surface.
The scientists quickly weighed and measured the fish, took a snapshot and then released it back into the water. But it was enough documentation to ensure that news of the discovery spread.
Map of the section of the North Shore Channel, in the Lincolnwood neighborhood of north Chicago, where the spotted gar was found.
The straight, dark line to the left is the North Shore Channel in the Lincolnwood neighborhood of north Chicago, where the spotted gar was found between Touhy and Pratt.

“Gar-in-the-city” stories landed in outlets like the Chicago Sun Times, CBS Chicago, and even National Geographic. And, of course, it caught the attention of our favorite friend of primitive fishes – Solomon David. (who is quoted in many of those news articles)
David is a post-doctoral researcher with the Center for Limnology, but spends most his time at Chicago’s iconic Shedd Aquarium, in the Daniel P. Haether Center for Conservation and Research, which co-supports his position. We asked David for his thoughts on a spotted gar in an urban waterway.
We knew the discovery of a gar in the waterways of your own backyard would catch your eye, but what can we take away from a single fish found where it was unexpected?
Solomon David
Solomon David

David: With just one fish it is hard to say. Generally spotted gar need clear, clean water and pretty lush vegetation, or plant cover growing in that habitat. So maybe the habitat there or somewhere close by is of decently high quality. But, again, it’s just one fish, so there’s not a lot we can say yet with confidence.
Okay then, so what excites you most about the discovery?
David: It’s a great mystery. With the Chicago fish, what’s interesting is we don’t know where it came from. It’s sort of in the middle of the known Great Lakes population [of spotted gar] and the Mississippi Basin population. So it was found in what’s been thought of a sort of “dead zone,” in terms of the presence of spotted gar. From what we know, it’s not supposed to be here. But it didn’t come from outer space, so where?
In general, spotted gar aren’t the best dispersers, in terms of river systems. Long-nose and short-nose [gar] are better riverine dispersers, which means individual fish will sort of prospect and push the boundaries more of their known distributions.
You did your dissertation work at the University of Michigan on spotted gar. What were you studying? What did you find?
David: I was looking at the conservation of the peripheral population of fish species and we used spotted gar as the species.
Spotted gar. Courtesy: Solomon David
Spotted gar. Courtesy: Solomon David

With any species, most exist in what’s called the “core population” and that is usually a “softer environment,” a place where it’s easier for whatever them to thrive, a place with conditions that are more comfortable, like milder temperatures, longer growing seasons and available food sources.
But, in relatively harsher environments on the edge of the species’ range, places with smaller amounts of food, flashier temperatures, and shorter growing seasons, you find these “peripheral populations.” They’re at the frontier of their species. In spotted gar, the Great Lakes population is “peripheral” and the “core” population is in the MIssissippi drainage. [Waterways of states like Louisiana, Alabama and Arkansas].
We were looking for adaptations in the peripheral Great Lakes population.
Did you find any evidence of adaptations?
The red circle indicates the "core" distribution of spotted gar. The blue circle is the peripheral Great Lakes population. Courtesy: Solomon David
The red circle indicates the “core” distribution of spotted gar. The blue circle is the peripheral Great Lakes population. Courtesy: Solomon David

David: One thing we found is a big difference in the size and growth rates between the peripheral and core species. We collected embryos from both populations and put them in a “common garden” experiment, essentially, where both fish grow up in completely similar conditions. And, sure enough, the peripheral population had a higher growth rate.
Why would the peripheral population have a higher growth rate in the “fringe” habitat where there’s less food and colder, shorter growing seasons?
David: Well, weight is what you usually need to survive the winter. Down in the south the fish might have all year to grow because of warmer environments, so they grow at a sort of “slow and steady” pace. But, as you go north, the growing season gets shorter and shorter and these fish need to be bigger in size so that they have more reserves to pull from so that they don’t starve during winter. And that means they’ve got to grow up quickly.
In a given spawn of fish, you’ve got runts and average sized fish and then bigger fish. And, theoretically, if winter comes and the ones survive the winter, they are then left to pass on their genes. If you cycle through that for thousands of years, you should see a population difference. And that’s what we think we see with spotted gar, the peripheral Great Lakes population produces heavier, longer and longer-lived fish than their “core” population counterparts in the south.

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