Juvenile growth of a macrohabitat generalist tied to hydrological character of large‐river system

Abstract

Summary Characteristics of river hydrology, including components of the natural flow regime, have been used to describe fish growth patterns. Contradictory growth responses among species, life‐stages within species and river systems suggest that eco‐hydrological relationships may not be scalable to all species and river systems; thus, increased knowledge regarding growth–flow relationships among a greater diversity of taxa and river systems may aid conservation and management of riverine fishes. We used channel catfish (Ictalurus punctatus: Ictaluridae), and a set of candidate mixed‐effect linear models to assess juvenile fish growth in relation to components of the flow regime within the Lower Platte River (LPR), Nebraska, U.S.A. The LPR is subjected to extremes in river flow conditions from both natural and anthropogenic sources, and provides a model system with which to assess growth–flow relationships. Juvenile channel catfish growth was influenced by the duration, magnitude and timing of in‐channel flows. Specifically, sustained high‐flow periods during the spring increased growth; whereas, reduced growth occurred during prolonged periods of low‐flow conditions within the LPR. Differences in juvenile channel catfish growth with respect to changing flow conditions may be due to changes in river productivity between low‐ and high‐flow conditions; thus, we discuss the applicability of alternative river production models with respect to juvenile fish growth in wide braided river systems such as the LPR. Reduced duration and changes to the timing of high‐flow periods may result in a myriad of deleterious effects including as our study shows, exacerbating slow growth of juvenile channel catfish and potentially other fishes with similar flow requirements. Conservation and management of large‐river species may benefit from water management policies that consider the complex and often contrasting growth responses of lotic fishes as well as the importance of using multiple aspects of the flow regime when assessing ecological responses.