Seasonal fish community and reproductive biology of fishes in two tributaries of the lower Missouri River, USA

Tributaries provide important habitats for spawning, rearing and feeding of fish in connected river systems. Regulation of rivers may alter the fish communities and environmental variables triggering fish use. Habitat destruction from dam construction is one of the leading causes for the decline of aquatic species, including big-river fishes. The influence of larger dams on fishes is well-documented and low-head dams (<15 meters in height) are receiving increased attention as removal of these structures occurs because of an emphasis on restoring rivers for aquatic fauna and public safety. However, the distribution of mainstem big-river fishes in tributaries and the contribution of tributaries to large river systems (LRS; systems with a mean annual discharge of at least 350 cms) remains unclear. Therefore, this study investigated the seasonal patterns of fish abundance, species richness, and big-river fish presence upstream and downstream of a low-head dam (LD1) on the Osage River, a regulated tributary of the Lower Missouri River in central Missouri, as well as in comparison to the geographically and biologically similar free-flowing Gasconade River, another tributary to the Lower Missouri River. Furthermore, this study investigated the influence of river regulation in the Osage River on reproductive biology of fishes by comparing sex and reproductive readiness of Golden Redhorse and Spotted Bass in the two tributaries. ... These results will provide a baseline should modifications occur to LD1 in the Osage River, and provides evidence that big-river fishes seasonally use Missouri River tributaries and that LD1 is a semi-permeable barrier to big-river fish in the Osage River. Our findings suggest that species change in the lowermost sections of tributaries near confluences with LRS is seasonally influenced and provides habitats for a variety of life stages, including nursery habitat. Managers and researchers should incorporate tributaries of various sizes into investigations of this nature for big-river species and that this use may be limited to the lowermost reaches. The cues for reproductive readiness in the regulated Osage River and the free-flowing Gasconade River do not differ for Golden Redhorse yet river regulation (i.e., Osage River) was a substantial predictor of Spotted Bass reproductive readiness.