Can brook trout survive climate change in large rivers? If it rains

Abstract

We provide an assessment of thermal characteristics and climate change vulnerability for brook trout (Salvelinus fontinalis) habitats in the upper Shavers Fork sub-watershed, West Virginia. Spatial and temporal (2001-2015) variability in observed summer (6/1-8/31) stream temperatures was quantified in 23 (9 tributary, 14 main-stem) reaches. We developed a mixed effects model to predict site-specific mean daily stream temperature from air temperature and discharge and coupled this model with a hydrologic model to predict future (2016-2100) changes in stream temperature under low (RCP 4.5) and high (RCP 8.5) emissions scenarios. Observed mean daily stream temperature exceeded the 21°C brook trout physiological threshold in all but one main-stem site, and 3 sites exceeded proposed thermal limits for either 63- and 7-day mean stream temperature. We modeled mean daily stream temperature with a high degree of certainty (R=0.93; RMSE=0.76°C). Predicted increases in mean daily stream temperature in main-stem and tributary reaches ranged from 0.2°C (RCP 4.5) to 1.2°C (RCP 8.5). Between 2091 and 2100, the average number of days with mean daily stream temperature>21°C increased within main-stem sites under the RCP 4.5 (0-1.2days) and 8.5 (0-13) scenarios; however, no site is expected to exceed 63- or 7-day thermal limits. During the warmest 10years, ≥5 main-stem sites exceeded the 63- or 7-day thermal tolerance limits under both climate emissions scenarios. Years with the greatest increases in stream temperature were characterized by low mean daily discharge. Main-stem reaches below major tributaries never exceed thermal limits, despite neighboring reaches having among the highest observed and predicted stream temperatures. Persistence of thermal refugia within upper Shavers Fork would enable persistence of metapopulation structure and life history processes. However, this will only be possible if projected increases in discharge are realized and offset expected increases in air temperature.

Stream channel restoration increases climate resiliency in a thermally vulnerable Appalachian river

“…We observed the greatest decrease in warming downstream of major tributaries, where channel narrowing increased transport and decreased warming of cold‐water inputs. These results add to an increasing number of studies documenting the importance of network topology and cold‐water inputs on the thermal regimes of this (Merriam et al ) and other larger‐river systems (Kiffney et al ; Rice et al ; Ebersole et al ; Fullerton et al ). However, ours is the first study to consider and document thermal benefits of in‐stream restoration within the context of major tributary inputs and associated thermal discontinuities and highlights the need to account for these complexities to maximize and realize potential benefits of restoration.…”

Seasonal streamflow extremes are key drivers of Brook Trout young‐of‐the‐year abundance

“…Furthermore, the effects of summer conditions have been studied extensively; abundance has consistently been found to be positively correlated with summer streamflow and negatively correlated with summer temperature (Nislow et al 2004, Xu et al 2010a, Warren et al 2012, Letcher et al 2015b, Kovach et al 2016, Merriam et al 2017). Furthermore, the effects of summer conditions have been studied extensively; abundance has consistently been found to be positively correlated with summer streamflow and negatively correlated with summer temperature (Nislow et al 2004, Xu et al 2010a, Warren et al 2012, Letcher et al 2015b, Kovach et al 2016, Merriam et al 2017).…”

Extreme heat events and the vulnerability of endemic montane fishes to climate change

“…First, sub-lethal thermal physiology could increase or decrease individual energy budgets depending on seasonal changes in growing-degree days and prey availability (Ries and Perry 1995). Altered flow regimes may also affect fishes indirectly by altering air-water temperature relationships and subsequent thermal habitat conditions (Merriam et al 2017). Alternatively, warming at cold-edge limits could enhance growth and recruitment, allowing upslope range expansions (Lawrence et al 2015).…”

“…Indeed, our inability to consistently model water temperatures from air temperature and landscape features using different statistical algorithms contributed the most uncertainty to our projections of warming tolerance. For example, Merriam et al (2017) identified low flows in combination with high air temperatures contributing to thermal stress of Brook Trout in central Appalachian streams. This statistical property is not explicitly incorporated into our stochastic air temperature simulations, meaning that our estimation of T extreme events could be conservative.…”