LOTIC FISH-COMMUNITY STRUCTURE FOLLOWING TRANSITION FROM SEVERE DROUGHT TO HIGH DISCHARGE

A survey of fishes in the Little Missouri River, North Dakota, was made in July of the unusually wet summer of 1993, following a six-year period of drought. During the nine-day study period, water velocities were high (0.4 to 0.87 m/s), and water temperatures, levels, and discharges fluctuated dramatically in response to rainfall. Only thirteen species of fishes were collected within the 190-km study reach. Of these, only three were found regularly; the others were collected in unusual habitats such as small tributary streams and beaver dams. The three common species (Platygobio gracilis, Hybognathus placitus, and Rhinichthys cataractae) comprised 95% of individuals captured and are known to be well adapted to high flow. The fish community was somewhat different and much less diverse than in the past, possibly due to the preceding drought, high discharge, or rapid transition between them. Ten species found previously were not collected; five of these were abundant. Six species collected were not previously found in the study reach and two of these (Phoxinus eos and Pimephales notatus) are apparently new records for the Little Missouri River. The sturgeon chub (Macrhybopsis gelida) was not collected, even though it was common in the Little Missouri River as recently as the late 1970s, and is well adapted to high flow and turbid water.