Intraspecific variability in thermal tolerance: a case study with coastal cutthroat trout

Abstract

Fish physiological performance is directly regulated by their thermal environment. Intraspecific comparisons are essential to ascertain the vulnerability of fish populations to climate change and to identify which populations may be more susceptible to extirpation and which may be more resilient to continued warming. In this study, we sought to evaluate how thermal performance varies in coastal cutthroat trout (Oncorhynchus clarki clarki) across four distinct watersheds in OR, USA. Specifically, we measured oxygen consumption rates in trout from the four watersheds with variable hydrologic and thermal regimes, comparing three ecologically relevant temperature treatments (ambient, annual maximum and novel warm). Coastal cutthroat trout displayed considerable intraspecific variability in physiological performance and thermal tolerance across the four watersheds. Thermal tolerance matched the historical experience: the coastal watersheds experiencing warmer ambient temperatures had higher critical thermal tolerance compared with the interior, cooler Willamette watersheds. Physiological performance varied across all four watersheds and there was evidence of a trade-off between high aerobic performance and broad thermal tolerance. Given the evidence of climate regime shifts across the globe, the uncertainty in both the rate and extent of warming and species responses in the near and long term, a more nuanced approach to the management and conservation of native fish species must be considered.

Population variability in thermal performance of pre-spawning adult Chinook salmon

“…Our findings indicate that migration history (temperature and physical challenges) plays an important role in population thermal performance and physiological capacities. Intraspecific variability is not uncommon in other salmonids ( Lee et al, 2003b ; Eliason et al, 2011 ; Chen et al, 2013 , 2015 , 2018 ; Stitt et al, 2014 ; Verhille et al, 2016 ; Whitney et al, 2016 ; Poletto et al, 2017 ; Abe et al, 2019 ; Anttila et al, 2019 ; Zillig et al, 2021 ; Anlauf-Dunn et al, 2022 ; Zillig et al, 2022 ) and in other fish species such as killifish and Atlantic cod ( Fangue et al, 2006 ; Lucassen et al, 2006 ). Our findings complement previous work in adult sockeye salmon and egg/embryo Chinook salmon from coastal vs .…”

“…5 ), which mark the maximum temperature below which fish are predicted to perform near optimally. Accordingly, Chilliwack and Shuswap Chinook salmon may have a functional warming tolerance (max environmental temperature-upper T pejus ) ( Anlauf-Dunn et al, 2022 ) of 2.8 and 2.6°C, respectively, en route to the spawning grounds. It is evident that current and in the near future, Fraser River temperatures are approaching the functional limits of Chinook salmon.…”

Move, migrate, or tolerate: Quantifying three tactics for cold‐water fish coping with warm summers in a large river

“…As a cold‐water stenotherm, coastal cutthroat likely experience thermal stress at temperatures higher than ~18°C (Sturdevant, 2008). Coastal cutthroat trout have received less physiological study than other salmonids; however, recent work by Anlauf‐Dunn et al (2022) has found that cutthroat from distinct Oregon watersheds shows considerable intraspecific variation in physiological performance and thermal tolerance. The upper thresholds of thermal tolerance were likely related to the historical experience of temperatures within these watersheds.…”

Sixth Oregon climate assessment

“…This result surprised us because cutthroat trout are conspicuously abundant in thermal refuges during summer, but difficult to observe in the mainstem due to sampling restrictions and low water clarity. Presenceabsence data might lead one to assume that the mainstem was too warm for cutthroat trout during summer, yet the vast majority of tracked fish did not leave the mainstem even as it reached temperatures that likely were physiologically suboptimal (Anlauf-Dunn et al 2022).…”