Assessing the Distribution and Habitat of Iowa Darters (Etheostoma exile) in Illinois

The Iowa Darter (Etheostoma exile) is a state-threatened fish species inhabiting a limited range in northern Illinois. Historical surveys (from 1901-1995) found Iowa Darters at only 40 sites, with 19 sites being from glacial lakes near the Wisconsin border leading to the conclusion they primarily inhabited glacial lakes. Recent surveys (since 1995) have found E. exile at 37 sites, with only 13 of those sites being from glacial lakes. Many of the recent surveys have focused on headwater streams that have had limited to no previous records of fish sampling. The combined findings illustrate the need to evaluate whether populations of Iowa Darters routinely inhabit the headwater streams of northern Illinois. Using the recent collection locations, species distribution models were created to guide future sampling in streams potentially having E. exile populations. Models indicated many of the potential locations for E. exile are headwater streams with no previous history of fish community sampling. Targeted sampling in areas of high probability supported model predictions and have provided multiple new localities of Iowa Darter populations. Our results have changed what we know about the range of Iowa Darters in Illinois and have granted new insight of local habitat needs.