Spatial Variability of Silver Carp Population Demographics in a Large Tributary River

Abstract

Silver Carp Hypophthalmichthys molitrix have expanded their range to encompass most of the Mississippi River basin, including much of the Missouri River. However, there is a paucity of information concerning Silver Carp in the Missouri River basin, especially in tributaries. Little is known about how Silver Carp function in these tributaries or how connectivity with a main‐stem river can influence population demographics within either system. The Kansas River is a tributary to the Missouri River and has multiple physical anthropogenic barriers creating varying levels of connectivity within the system, as well as with the Missouri River. These varying levels of connectivity, or lack thereof, provide a unique opportunity to examine population demographics in river segments separated by barriers. We collected Silver Carp from upstream and downstream of the first two barriers on the Kansas River in the summers of 2018 and 2019. No Silver Carp were captured upstream of a hydropower dam at river kilometer 84 but were found upstream of a water diversion weir at river kilometer 24. Catch rates of adult Silver Carp were lower in the reach above the weir, but Silver Carp caught in this reach exhibited greater growth rates than Silver Carp captured below the weir. Catch rates of juveniles were also lower in the reach above the weir. Limited connectivity within the Kansas River via the water diversion weir could influence size structure and catch rates of Silver Carp captured above and below the weir. Lack of juveniles above the weir indicates that reproduction may be limited in this reach, and river conditions below the weir may be more suitable for rearing juvenile Silver Carp. This information is important for understanding Silver Carp population demographics across a range of river environments, providing critical information for the development and implementation of broadscale control plans.