Effects of Substrate on Movement Patterns and Behavior of Stream Fish through Culverts: An Experimental Approach

Culverts can provide a significant barrier to fish passage by fragmenting fish habitats and impeding the passage success of small-bodied fish. Geographical connectivity is critical to the maintenance of diverse fish assemblages. Culverts with high cross-sectional velocity can cause population fragmentation by impeding passage of small, freshwater fish. Behavioral responses of small fish to high velocities can differ among functional groups, and swimming behavior of many species is not well known. We tested effects of substrate type on swimming behavior in two small, freshwater fish species—southern leatherside chub (Lepidomeda aliciae, a midwater species), and longnose dace (Rhinichthys cataractae, a benthic species)—across three substrate treatments: (1) a bare flume, (2) large flow obstacles, and (3) a natural cobble substrate. Both longnose dace and southern leatherside chub used paths of low velocity and swam in the near-substrate boundary area. Fish in the bare flume and large obstacle treatments swam along the corners of the flume in a straight swim path, whereas fish in the natural substrate treatment used all parts of the flume bed. There was no relationship between passage success of fish and substrate type, fish species, or their interaction. In contrast, substrate type, fish species, and their interaction were significant predictors of passage time. Southern leatherside chub passed through the test section about two to four times faster than longnose dace. Both species took longer to pass through the large flow obstacle treatment compared to the bare flume or natural substrate. The natural substrate created a complex velocity profile with areas of low velocity throughout the entire flume, in contrast to the other two treatments. Our data suggest natural substrates can improve the passage of small fish in high-velocity culverts for both benthic and midwater functional groups.

Status, Distribution, and Conservation of Native Freshwater Fishes of Western North America

ABSTRACT Outside of anadromous salmonids and a few endangered species, the biology of native freshwater fishes of western North America is poorly known. What do we need to know to effectively manage native species and avoid decline and extinction? A recent analysis of the role of science in the Pacific salmon controversy outlines a clear framework for biological evaluation and management of native species. This framework has three components: (1) determine the status of populations based on genetic and ecological variation, (2) identify and quantify threats to populations, and (3) determine actions to alleviate threats and promote conservation of populations.We use our studies of leatherside chub <em>Gila copei</em> (also known as <em>Snyderichthys copei</em>), a small cyprinid native to the Bonneville basin and upper Snake River drainage, as a case study to illustrate the application of this research and management framework. Recent surveys have revealed dramatic reductions in range of leatherside chub over the last 50 years. Genetic, morphometric, and ecological studies all indicate that leatherside chub comprise two distinct species. Leatherside chub is threatened by both habitat degradation and introduced brown trout <em>Salmo trutta</em>, and the interaction between these two threats exacerbates negative effects.We conclude by showing how studies of leatherside chub can inform and influence management, conservation, and habitat restoration activities.