Relations between Physicochemical Factors and Abundance of Fishes in Tributary Confluences of the Lower Channelized Missouri River

Abstract

We sampled fish from seven tributary confluences in the lower channelized Missouri River from June 1996 through July 1998 to examine the influence of physicochemical factors in the Missouri River and tributary confluences on the abundance of fishes in tributary confluences. Twenty-six species and one hybrid were collected during the course of the study, but 10 species (river carpsucker Carpiodes carpio, goldeye Hiodon alosoides, sauger Stizostedion canadense, common carp Cyprinus carpio, shortnose gar Lepisosteus platostomus, freshwater drum Aplodinotus grunniens, channel catfish Ictalurus punctatus, gizzard shad Dorosoma cepedianum, white crappie Pomoxis annularis, and smallmouth buffalo Ictiobus bubalus) composed 90% of the fish collected. Catch per effort (log₁₀[(number of fish/100 m²) + 1]) of fishes was significantly greater in early spring (March 1997) and summer (June 1996) than in winter (December 1996 and January 1997) samples. Multivariate ordination partitioned physicochemical factors into two discrete principal components (PC) describing (PC 1) water temperature in the Missouri River and tributary confluences, and (PC 2) Missouri River turbidity, Missouri River discharge, maximum depth in tributary confluences, and turbidity in tributary confluences. Catch per effort of fishes in the tributary confluences was significantly related (R ² = 0.47, P < 0.0001) to PC 1 and PC 2 scores. Catch per effort was curvilinear along PC 1, but linear along PC 2 in the multiple regression model. Our results indicate that tributary confluences provide favorable habitat for several species in the lower channelized Missouri River. However, use of these habitats is strongly influenced by spatial and temporal changes in physicochemical factors in the Missouri River and tributary confluences and may be related to feeding, resting, and reproduction.