USFWS Grant: Climate Change Impact on Rio Grande Cutthroat Trout

The purpose of this project is to assess the effect of climate change on Rio Grande cutthroat trout (Onchorhynchus clarki virginalis) (RGCT) distribution. By tying together the temperature tolerance of RGCT to temperatures within current and potential streams, the level of threat that climate change poses to the species can be more accurately assessed.

The objectives are to compare historical and recent stream temperatures within the species range and assess the correlation between stream and air temperatures and between stream temperatures and environmental variables such as snow pack and discharge.

IV. BACKGROUND

In 2008, RGCT became a candidate species (73 FR 27900). Under Section E of the Candidate Assessment, the predicted effects of climate change on RGCT were discussed extensively because there are several mechanisms through which climate change could affect the subspecies. One of the primary ways that RGCT may be affected is through increased water temperature throughout its life cycle.

Coldwater trout require a rather narrow range of cool to cold water habitat. Temperature preferences and tolerances for RGCT have not yet been studied. Although research is underway to investigate environmental temperature preferences for the species, a more complete picture of the effects of climate change is needed. To obtain a clearer picture, we need to understand the historical and current temperatures the species has or could potentially experience throughout its range.

The USGS Coop Unit at New Mexico State University currently has funding for the laboratory studies on RGCT temperature tolerance, making them the leader on RGCT temperature studies. This Cooperative Agreement will allow them to expand the interpretation of their laboratory studies to what is occurring in the field.

V. SCOPE

To understand changes that may be occurring at the landscape level, long-term historical stream temperature data from RGCT streams will be analyzed. Historical data will be mined from both federal and state agencies as well as the National Hydrology Dataset (NHD, NHD+, PRISM) to obtain average high temperature, low temperature, precipitation, and accumulated precipitation by month throughout specified watersheds. Number of days in which stream temperature exceeds 72, 75, and 80º F (22.2, 23.9, 26.7ºC) will also be tallied. Once the historical data is obtained, it will be organized and summarized in Microsoft ACCESS.

Monitoring stream temperatures occupied by RGCT is needed. Stream temperature is not only dependent on air temperature but also on runoff volume. Looking at the relationships among these factors will be very important to our understanding of stream temperature extremes and variability. For that reason, watersheds that are occupied by RGCT, have a SNOTEL snow gage, and a stream gage have a high priority for monitoring. Because of annual variability in precipitation and temperature, it is envisioned that this will be a multi-year project that will track snow pack, runoff, and stream temperature for many years. Although only one year of research is currently funded, it is anticipated that additional funds will be obtained for long-term monitoring. From the analysis of historical data, recommendations for the deployment of thermographs will be made to obtain current data for comparison with historical data.

The Service is striving to become a leader in assessing the effects of climate change on fish and wildlife. The Service contact person for this Cooperative Agreement wrote the status review for RGCT which included a large section on the potential effects of climate change on RGCT. The Service will provide guidance, expert knowledge, and serve as a resource for the graduate student conducting this research. Monthly calls will be made to monitor progress, provide suggestions, and evaluate the results of the research.