Thermal landscapes in a changing climate: biological implications of water temperature patterns in an extreme year

Abstract

Record-breaking droughts and high temperatures in 2015 across the Pacific Northwest, USA, provide an opportunistic glimpse into potential future thermal regimes of rivers and their implications for freshwater fishes. We applied spatial stream network models to data collected every 30 min for 4 years at 42 sites on the Snoqualmie River (Washington, United States) to compare water temperature patterns, summarized with relevance to particular life stages of native and nonnative fishes, in 2015 with more typical conditions (2012–2014). Although 2015 conditions were drier and warmer than what had been observed since 1960, patterns were neither consistent over the year nor on the network. Some locations showed dramatic increases in air and water temperature, whereas others had temperatures that differed little from typical years; these results contrasted with existing forecasts of future thermal landscapes. If we will observe years like 2015 more frequently in the future, we can expect conditions to be less favorable to native, cool-water fishes such as Chinook salmon (Oncorhynchus tshawytscha) and bull trout (Salvelinus confluentus) but beneficial to warm-water nonnative species such as largemouth bass (Micropterus salmoides).

Individual‐based simulations suggest mixed impacts of warmer temperatures and a nonnative predator on Chinook salmon

“…A strong phenological shift could result in such a loss of life history strategies (Beechie et al 2006, Crozier et al 2008 a , Boughton et al 2015). Furthermore, the Snoqualmie River typically has a snowmelt‐driven hydrological peak, but that peak was absent in 2015 (Kubo 2016, Steel et al 2019), and areas with rainfall‐dominated hydrology tend to produce more subyearling migrants (Beechie et al 2006). Warm thermal regimes, like that observed 2015, may result in fewer salmon remaining instream over winter.…”

“…2). The 2015 thermal regime may be illustrative of conditions more likely to occur in the future as the climate warms (Kubo 2016, Steel et al 2019). We included largemouth bass to evaluate how Chinook salmon were affected by a nonnative predator.…”

“…In addition to concerns about shifted salmon life histories, there is a growing concern that warmwater nonnative species such as bass will expand their range as the climate warms, potentially squeezing salmon out of preferred habitats (Hulme 2007, Lawrence et al 2014, Cheng et al 2017. In the Snoqualmie River, Steel et al (2019) Fig. 8.…”

Snake River sockeye and Chinook salmon in a changing climate: Implications for upstream migration survival during recent extreme and future climates

“…We can expect many more years as warm as 2015, but in the future, abnormally high temperatures will likely continue throughout summer rather than abating as they did in 2015. Furthermore, projections display much greater spatial homogeneity in future years than was observed in 2015 [79], putting many more localities at high risk. As record-breaking climatic conditions occur more frequently, careful examination of the complex environmental and anthropogenic changes that threaten existing biodiversity is a growing conservation imperative.…”

Shifting Perspectives in Assessing Socio-Environmental Vulnerability

“…Because there can be considerable uncertainty associated with localized forecasts, USFS guidance on VAAs [14] urges staff on individual national forests to proceed with VAAs even without finely downscaled climate projections. Often existing information, such as historical information on climate change and observations in extreme years, can be used for framing climate change in terms that are clearly understood and appreciated [37]. In fact, the ranges and directions of projected change may be more important than specific estimates for future temperature and runoff [14].…”