Cooperative Fish and Wildlife Research Units Program: New Mexico
Education, Research and Technical Assistance for Managing Our Natural Resources

The Rio Grande cutthroat trout (Oncorhynchus clarki virginalis) is the southern-most subspecies of cutthroat trout in the Western U.S., endemic to the Rio Grande, Pecos, and Canadian River basins in Colorado and New Mexico (Behnke 2002). Historically the subspecies occupied over 10,000 km of streams in this region, but currently occupies less than 12% of its historical range (1,500 km) with as few as 120 remaining conservation populations (Alves et al. 2008). In 2008, O. c. virginalis was added to the Endangered Species Act Candidate List, and the potential negative effects of climate change on this subspecies were discussed in detail in the listing package and included concerns about both water temperature and low flow. To help resolve some of the uncertainty related to climate vulnerability of existing O. c. virginalis core conservation populations, our research group initiated a monitoring effort in 2010 to characterize both stream temperature regimes and baseflow hydrology within 40 core conservation populations. Importantly, our fall baseflow measurements revealed that more than 67% of O. c. virginalis study streams exhibited discharge levels less than 1.0 cubic feet per second (cfs), with one completely dry site (Figure 1a), despite an above-normal 2010 snowpack throughout the majority of the sub-species range. In 2011, the basin experienced moderate to severe drought-conditions during the early summer, however, late-season rains likely reduced the impact of those early drought conditions. In 2011, fall baseflow conditions were documented with similar percentage of low flow streams within an expanded subset of O. c. virginalis streams (Figure 1b). Importantly, because our baseflow measurements occur at a single point during the late fall, the flow conditions during the driest portions of 2011 went undocumented. Low snowpack and resultant potential for flow intermittency and low baseflows has a high likelihood of negatively affecting O. c. virginalis populations, as was observed in 2002 when several populations were extirpated by drought due to low snowpack during the previous winter (Japhet et al. 2007; Patten et al. 2007). The extent of negative impact of the 2002 drought is unknown, as only a small subset of O. c. virginalis core-conservation populations were visited immediately following the drought to evaluate its impact.