DNR fisheries biologists will conduct standard fish surveys at 16 Northern Indiana natural lakes this month as part of an annual project to monitor the long-term status and trends of fish populations in the region’s lakes.
Lakes to be surveyed are: Adams and Royer lakes in LaGrange County; Indiana Lake in Elkhart County; Hill, McClure, and Waubee lakes in Kosciusko County; Crooked, Gordy and Miller lakes in Noble County; Flint Lake in Porter County; Riddles Lake in St. Joseph County; Arrowhead, Hamilton, Little Lime, and Silver lakes in Steuben County, and Little Cedar Lake in Whitley County.
During the surveys, biologists will use electrofishing boats, gill nets, and trap nets to capture fish. Each fish will be identified, measured and released. Scale samples will be taken from popular sport fish to determine their growth rate. The surveys are conducted over two days.
“Our sampling gives us a basic picture of the fish species, their number and their size,” said Steve Donabauer, a DNR research biologist who is overseeing the project. “Because the lakes are chosen randomly and represent a variety of lake habitats, we can put together a composite view of how fish populations are changing through time.”
Donabauer has already identified some trends based on earlier results.
“Since the mid-1980s, we’ve seen a two-fold increase in the number of 14-inch and greater legal-size largemouth bass and a three-fold increase in bluegills greater than eight inches,” he said.
Donabauer thinks the increase in bass numbers is due to larger minimum size limits established in the late 1990s and an increase in catch-and-release fishing. This has led to greater bass predation on bluegills. As a result, fewer bluegills survive but those that do have more food and grow larger.
In contrast, the survey results indicate some fish are declining.
“There has been a subtle decrease in species richness,” Donabauer said. “Our data suggest that the loss of one species from a lake over a 15-year period is the new norm.”
Species showing the largest declines are those that Donabauer describes as “cool-water” fish. These are generally found in clean lakes where oxygen is present in deeper, cooler water.
“Northern pike is a good example of a cool-water fish,” Donabauer said. “They survive, grow, and reproduce best where water temperatures are less than 73 degrees and at least three parts per million of oxygen occur.”
As lakes age and become nutrient enriched, they can lose their layer of cool-water habitat and stress fish that depend on it.
Pike were found in 40 percent of our lakes in the 1980s. Now that figure has dropped to 30 percent, Donabauer said.
“This is the type of information we get from surveys and is crucial for us to understand what’s going on in lakes,” Donabauer stated. “More important, it serves as a basis for taking corrective management actions and provides a way to measure their success.”