This project aims to improve existing models of stream baseflow in California’s streams and rivers, and assess the sensitivity of native fish species to the natural variability of baseflows in systems with unimpaired and impaired flow regimes. Improving the body of scientific knowledge around the relationship between native fish and baseflow conditions will be key to informing management of freshwater environments to promote fish conservation and sustainability.  

Anthropogenic impacts on California’s waterways have left much of the state’s freshwater fish species imperiled. Water infrastructure, agriculture, and urbanization have had a significant impact on freshwater flow regimes in California. Moyle et al. (2011) estimated that more than 83% of the state’s native freshwater fishes are at risk of extinction over the next century. As a result, there is a particular need to better understand how native fishes respond to altered flow regimes.  

Native fishes are especially vulnerable to flow alteration during low-flow periods, when surface water diversions, groundwater pumping, and impoundments can limit stream connectivity, reduce water quality, and dry river channels (Rolls and Bond 2017). These flow impacts are most evident during the dry summer season, when streamflow naturally recedes to low-flow conditions (dry season baseflow), but low flows can also occur in the wet-season during periods between storms (wet season baseflow). 

Assessing the vulnerability of native fishes to dry- and wet-season baseflow alteration first requires an understanding of natural flow variation and the hydrologic processes that sustain baseflow. Predictions of natural, unimpaired flows provide a baseline from which to assess the degree of flow deviation under current or future conditions. Recently, such predictions of unimpaired flows have been developed as part of a coordinated statewide effort to improve environmental flow management, known as the California Environmental Flows Framework (CEFF) (ceff.ucdavis.edu).  CEFF uses a Functional Flows approach that identifies components of the natural flow regime that are known to support important biophysical processes and promote conditions under which native species can flourish (Yarnell et al. 2015, Stein et al. 2021) Combined with information on flow requirements of native fish species, these data could be leveraged to explore potential relationships between native species and their vulnerability to changes in baseflow conditions resulting from water management activities and climate change.

The current project is intended to achieve two primary goals: (1) increase the accuracy of CEFF models for predicting key functional flow components, including wet and dry season baseflows, and (2) accurately assess the sensitivity of native fish species to changes in stream baseflow.

We will improve model accuracy through the incorporation of additional model predictors (local channel geomorphology, springs, soils, and catchment properties) of baseflow to better predict baseflow hydrology in ungauged and impaired systems. Additionally, we will develop models of additional baseflow metrics to accurately quantify minimum flows and the number of zero flow days.   

Expanding on previous efforts by Obester et al. (2022), we will systematically evaluate the life history requirements of native fish species relative to dry season baseflows. The California Department of Fish and Wildlife has collected long term, comprehensive fish monitoring data throughout the state that we will analyze in order to quantify effects of baseflows on fish communities. These analyses will focus on how species composition (including abundance of native and non-native species) and the life history, physiological, and morphological traits of fishes change over space and time in response to natural variation of the streamflow regime. Establishing quantitative relationships between baseflow conditions and fish life history characteristics has the potential to inform sustainable management of fish populations and environmental flow recommendations in streams throughout the state.

References:

Rolls, R. J., and N. R. Bond. 2017. Environmental and ecological effects of flow alteration in surface water ecosystems. Water for the Environment: From Policy and Science to Implementation and Management:65–82.

California Environmental Flows Framework Technical Team (2021). The California Environmental Flows Framework. University of California, Davis. http://ceff.ucdavis.edu.

Moyle, P.B., J.V.E. Katz and R.M. Quiñones. 2011. Rapid decline of California’s native inland fishes: a status assessment. Biological Conservation 144: 2414-2423. https://doi.org/10.1016/j.biocon.2011.06.002. 

Obester, A.N., Lusardi, R.A., Santos, N.R., Peek, R.A. & Yarnell, S.M. (2022). The use of umbrella fish species to provide a more comprehensive approach for freshwater conservation management. Aquatic Conservation: Marine and Freshwater Ecosystems, 32( 1), 112– 128. https://doi.org/10.1002/aqc.3746.

Stein, E.D., J. Zimmerman, S.M. Yarnell, B. Stanford, B. Lane, K.T. Taniguchi-Quan, A. Obester, T.E. Grantham, R.A. Lusardi, and S. Sandoval-Solis. (2021). The California Environmental Flows Framework: Meeting the Challenges of Developing a Large-Scale Environmental Flows Program. Frontiers in Environmental Science 9:769943. doi: 10.3389/fenvs.2021.769943.

Yarnell, S.M., G.E. Petts, J.C. Schmidt, A.A. Whipple, E.E. Beller, C.N. Dahm, … J.H. Viers. (2015). Functional Flows in Modified Riverscapes: Hydrographs, Habitats and Opportunities. BioScience, biv102. doi: 10.1093/biosci/biv102.