Seasonal fish assemblage structure in riffles, wadeable pools and non-wadeable pools of a perennial warmwater river

Abstract

Research on intermittent streams has linked deep pools with successful completion of critical life history requirements; however, few studies have investigated this concept in larger rivers. I compared fish assemblages, including species richness and fish density, in riffles, wadeable pools, and non-wadeable pools of the Neosho River, a 5th- order perennial warmwater river in Kansas, USA. Samples were collected by trawl during spawning and post-spawning seasons at eight sites from May to November 2018. I predicted that these mesohabitats would support disparate fish assemblages that changed in structure seasonally. I found that spatial patterns of fish assemblage structure were largely explained by differences between riffle and pool samples, consistent with that prediction. Species composition also varied between wadeable and non-wadeable pools, with Ghost Shiner (Notropis buchanani) abundance greatest in non-wadeable pools and Shortnose Gar (Lepisosteus platostomus), Smallmouth Buffalo (Ictiobus bubalus), and White Crappie (Pomoxis annularis) collected only in this mesohabitat. Temporal patterns

reflected higher species richness and fish density during spawn than post-spawn, with the density of fishes greatest in riffles and wadeable pools during the spawn but greatest in wadeable pools during post-spawn. Results were dependent on whether area- or volume based densities were analyzed, as more significant non-wadeable pool comparisons, higher riffle densities, and more indicator species were identified using volume-based densities. When sampling a diverse fish assemblage with species associated with surface, benthic, and water column habitats, both metrics and deep pools should be examined.