Flowing systems account for a small fraction of freshwater systems and support multiple biological hotspots of species diversity. Historically, patterns of species diversity can be attributed to habitat variation driven by natural processes such as seasonal flooding, underlying geology, and stream morphology. However, these stream habitat patterns have more recently been subjected to fragmentation and channelization caused by climate change and anthropogenic stressors. In this globally changing landscape, it is important to understand how habitat patterns are shifting and the resulting influences on the species dependent on them.

The Sandhills Ecoregion is in north-central Nebraska and spans 49,000 km² of grass-stabilized sand dunes characterized by mixed-grass prairies with sparse vegetation and sand topsoil. The connection between the Ogallala Aquifer and surface waters within the Sandhills Ecoregion maintains unique groundwater-fed streams. Streams within the Sandhills Ecoregion are characterized as clear and slow moving with cool water temperatures. Historically, Sandhills Ecoregion streams were highly connected to the floodplain providing ample feeding and spawning habitat. Further, there exists a limited human population density in the Sandhills Ecoregion. Land coverage is primarily pasture used for a mix between grazing and hay production. The hydrological characteristics and cool-water temperatures of Sandhills Ecoregion streams may afford a level of ecological resilience to fragmentation and changing climate conditions with limited information available on native species distributions and population demographics.

In collaboration with the Nebraska Game and Parks Commission and the Nebraska Natural Legacy Project, Nebraska Department of Environment and Energy, multiple landowners, University of Nebraska-Lincoln School of Natural Resources, and Nebraska CRU, the project goals are to build a knowledge base regarding the Sandhills Ecoregion and at-risk fish species therein. To achieve these goals, multiple projects are being conducted on Sandhills Ecoregion streams to characterize their environmental conditions along with species assemblages, distribution, and demographic rates.

Researchers are describing the associations between at-risk species and the abiotic and biotic environmental variables of the Sandhills Ecoregion using multi-scale, multi-species occupancy models. These models utilize multiple samples taken from the same reach to model the occurrence probability of target species while also accounting for imperfect detection. The target species of this project are: Finescale Dace Chrosomus neogaeus, Northern Pearl Dace Margariscus nachtriebi, Northern Redbelly Dace, Lake Chub Couesius plumbeus, Plains Minnow, and Flathead Chub.

This project will also seek to identify associations between temporal trends of species occurrence and anthropogenic stresses by resampling historical sites from statewide streams surveys. Results from this project will help describe which environmental variables and different scales species occurrence is associated with while also describing the anthropogenic stressors affecting species distribution.

An additional project aims to define the habitat needs of tier-1 species, Flathead Chub Platygobio gracilis, Plains Minnow Hybognathus placitus, and Northern Redbelly Dace Chrosomus eos, to explain and predict distribution in Nebraska streams using species distribution modeling.

Species distribution models predict the occurrence of species based on the statistical relationship between presence of a species and environmental conditions at multiple spatial or temporal scales. These models may be used to infer which environmental features are important to the distribution of tier-1 fish species in Nebraska, thus informing monitoring and management of these at-risk species.

Lastly, the team is conducting a study on Northern Pearl Dace Margariscus nachtriebi, which is a tier-II threatened species in Nebraska. The distribution of Northern Pearl Dace in Nebraska represents the southernmost extent of the species range and is isolated from the core distribution. Northern Pearl Dace in Nebraska reside in prairie streams of the Sandhills Ecoregion. Northern Pearl Dace are an important indicator species that is intolerant of degradation (decreased fish habitat, incision of the stream channel sedimentation, etc.) caused by stream geomorphic changes (i.e., channelization).

There is a lack of understanding regarding how stream geomorphic changes effect Northern Pearl Dace population demographics (i.e., survival, movement, abundance) and connectivity among Sandhills Ecoregion streams. Estimating the population size and survival of rare and at-risk species is challenging as capture-recapture data can be difficult to obtain. However, estimates of the effects of geomorphic alterations on these parameters are crucial to understand how degradation and restoration of distinct habitat features could impact Northern Pearl Dace populations.

The ONB features articles from Cooperative Fish and Wildlife Research Units across the country. Working with key cooperators, including WMI, Units are leading exciting, new fish and wildlife research projects that we believe our readers will appreciate reading about. This article was written by Jonathan Spurgeon, jspurgeon@usgs.gov, Assistant Unit Leader, Nebraska CRU, and Joseph Spooner, Braxton Newkirk, Connor Hart. Joe, Braxton, and Connor are M.S. students in Jonathan Spurgeon’s Lab.