The Use of Minor Postglacial Drainage Connections by Fishes in Indiana

Abstract

A DISTRIBUTIONAL study of the fishes of Indiana (Gerking, 1945) ofAl Xfered considerable evidence that minor postglacial connections between the Great Lakes and Mississippi drainages may have greatly influenced the northward dispersal of fishes by providing temporary pathways through otherwise impassable barriers. It has been known for some time that fishes used the major connections, i.e., the Chicago outlet and Maumee River, between these two drainages as they migrated northward during the ice retreat (Greene, 1935). Herman Wright (1932) traced the migration of certain freshwater snails through a minor glacial connection the KankakeeIroquois drainage to the upper Tippecanoe River, but other forms of aquatic life have not been studied this standpoint. Indiana was partially covered by both the Illinoian and Wisconsin glaciers, whose limits have been described by various authors, more recently by Thornbury (1937). The Illinoian glacier covered all of Indiana except an area in the southern portion extending the westernmost tip of the state upward to Bloomington and descending to the Ohio River at Jeffersonville. The Wisconsin glacier covered the northern two-thirds of the state with its southern boundary between the 39? and 40? parallels. The Huron-Erie lobe of the Wisconsin glacier retreated to the northeast and Lake Maumee, an early stage in the development of Lake Erie, was formed at its southern border. This lake extended into northeastern Indiana as far as Fort Wayne and its discharge was carried by the Maumee River to the Wabash River at Huntington. This connection between the present Great Lakes and Mississippi drainages existed for a considerable length of time and carried the bulk of the glacial water of the state. Melting ice the Michigan lobe of the glacier formed the beginning of Lake Michigan and its outlet (Chicago outlet) discharged into the Illinois River. Another major connection between the two great drainage systems was thus established. Both of these major connections accepted glacial water for a long period of time, perhaps 50,000 years, and there is no doubt that they were used by fishes in their northward dispersal. In addition to these major connections several minor ones existed in the northern part of the state. The Saginaw lobe, or middle lobe, of the Wisconsin glacier was first to retreat, and after the Michigan lobe had retreated far enough northward to allow westerly drainage, the upper Tippecanoe River was probably connected with the Kankakee and Iroquois rivers. Leverett (1915), who last worked on the glacial geology of that region, states that from near Ora in Starke County there may have been a northwestward drainage to the Kankakee as well as a southwestward drainage to the Iroquois. Later in the development of this region the St. Joseph River was probably connected with the Kankakee drainage at South Bend (Leverett, 1915). These connections probably existed a much shorter time than the two major connections mentioned above and it was not known whether fishes actually used these minor connections as they moved northward during the ice retreat.