Historical Changes in Large River Fish Assemblages of the Americas

<em>Abstract.</em>—The Patoka River drainage is a lowland-gradient watershed of the Wabash River lowlands in southwestern Indiana. During the late 18th century, the river was part of an extensive riparian floodplain wetland that connected the White River with the lower Wabash River. Through anthropogenic changes as a result of ditching, channelization, levee creation, coal extraction, and oil and gas exploration, the Patoka River drainage has been highly altered. These changes have resulted in a loss of sitespecific biological diversity and integrity, causing drainage-wide biological diversity decline. Extirpations in the watershed have resulted in the local loss of 12.7% of the fish fauna during the last century. The local extirpations of six species included central mudminnow <em>Umbra limi</em>, black redhorse <em>Moxostoma duquesnei</em>, brindled madtom <em>Noturus miurus</em>, bluebreast darter <em>Etheostoma camurum</em>, slenderhead darter <em>Percina phoxocephala</em>, and saddleback darter <em>P. vigil</em>. Black redhorse, bluebreast darter, slenderhead darter, and saddleback darter were only known from pre-1900, while brindled madtom and central mudminnow were known until the early 1940s. These species may have been rare to begin with in the Patoka River drainage, but since they are widespread elsewhere, it seems more probable that they disappeared as a result of the land-use changes. Sensitive species of darters and minnows have declined in abundance, but recent sampling has shown that they remain in the watershed at low abundance. Based on a probability sample, less than 12% of the channels represented reference least-disturbed conditions, while 61% exhibited degraded conditions.