Climate Change and the Rocky Mountains - Impact of Global Changes on Mountains: Responses and Adaptation - page 442

and biological changes, however, will not be uniform across aquatic
ecosystems in the Rockies.
A number of bioclimatic models have been developed for native
salmonids in the Rocky Mountain region—all of which forecast substantial
reductions in thermally-suitable habitats during the 21st century (Keleher
and Rahel 1996, Williams et al. 2009, Haak et al. 2010). These models
congruently show that as water temperatures continue to warm and exceed
species' physiological thresholds, populations will become increasingly
fragmented and will retreat into colder headwater habitats. For example,
using an upper temperature threshold of 22ºC as a constraint for cold water
trout and char (Keleher and Rahel 1996), models predict that an increase of
5ºC in mean air temperature would reduce the amount of thermally-suitable
salmonids habitat by 70% across the Rocky Mountain region. Wenger et al.
(2011b) forecasted the climate warming effects of increased temperatures
and altered fl ows on four interacting species of trout across the interior
western United States and predicted a 47% decline in total suitable trout
habitat by 2080. In the interior Columbia River basin, models predict that
bull trout ( Salvelinus confl uentus ) may lose 18-92% of thermally suitable natal
habitat due to climate warming over the next 50 or more years (Rieman et al.
2007). Jones et al. (2014) used a spatial hierarchical modeling framework to
predict stream temperatures and estimated that if average air temperatures
were to rise 3°C by 2050, bull trout would potentially lose 58% of foraging,
migrating and overwintering areas and 36% of spawning and rearing habitat
in the Flathead River system, Canada and USA.
Although increased stream temperatures will be one of the primary
consequences of a rapidly changing climate, increased disturbances and
altered fl ow regimes will also have a signifi cant impact on the persistence
of native salmonids and aquatic biota. Reduced snowpack, earlier and
more rapid spring runoff, increased fl oods, and drought all pose additional
stressors to native trout populations and aquatic organisms in western North
America (Poff 2002, Williams et al. 2009, Haak et al. 2010). In the western
United States, decreased snowpack and earlier spring runoff have been
linked to increases in the frequency and severity wildfi re (Westerling et
al. 2006), which are causing extensive habitat changes and, in some cases,
direct mortality of trout and other native fi shes. Interactions of stochastic
disturbances with fragmentation appear to be the greatest threats to the
persistence of small, isolated Colorado River cutthroat trout ( O. c. pleuriticus )
populations (Roberts et al. 2013). Similarly, decreasing summer habitat
volumes and increasing drought and wildfi re disturbances are perhaps
the greatest extirpation risks for remaining Rio Grande cutthroat trout
( O. c. virginalis ) populations, which are already highly fragmented
and confi ned to small (<10 km) headwater streams above natural and
anthropogenic barriers (Zeigler et al. 2012). Reduced snowpack and earlier