In hot water? Assessing the link between fundamental thermal physiology and predation of juvenile Chinook salmon

Abstract

In light of ongoing environmental change, understanding the complex impact of interacting stressors on species, communities, and ecosystems is an important challenge. Many studies to date examine the effects of potential stressors on a single species of concern. Yet these effects often resonate throughout a community and may produce changes in ecosystem dynamics that are equally critical to species resilience. The aim of this study was to develop a mechanistic understanding of how a rapidly changing stressor, water temperature, will alter trophic interactions among ectothermic fish species. In our region, California's Sacramento–San Joaquin River Delta system, it has been speculated that the decreased survivorship of juvenile Chinook salmon (Oncorhynchus tshawytscha) in warming waters may be caused partly by increased predation. Temperature influences metabolic rate functions and the amount of energy available for fitness‐relevant parameters (i.e., swim performance and escape response). Consequently, we hypothesized that these patterns of predation emerge due to a physiological advantage of predators over prey at warmer temperatures. To explore this, our first objective was to determine the fundamental thermal physiology of juvenile Chinook salmon and their potential predators in the Delta. Three physiological performance traits were measured for each species across a spectrum of temperatures: aerobic scope, burst speed, and the ability to burst repeatedly. For our second objective, we assessed whether the effect of temperature on these performance traits predicted the outcome of predation trials conducted across the same temperature spectrum. We found that temperature effects were species or population specific. Additionally, absolute burst swimming ability and the relative burst performance between predator and prey were stronger indicators of trophic dynamics than aerobic scope. Our analyses also confirmed that a major predator in the Delta, specifically largemouth bass (Micropterus salmoides), is more thermally adapted to higher temperatures and will likely consume salmon with an increasing frequency as waters warm. Thus, we show that an improved understanding of how fundamental thermal physiology impacts predation can provide ecosystem managers with better tools to predictively model predation upon juvenile salmon based on prevailing and future water temperatures.

Intraspecific variation among Chinook Salmon populations indicates physiological adaptation to local environmental conditions

“…However, these effects disappeared when populations were acclimated to 20°C, reflecting the shared decline in MMR and AS across populations. Reduced metabolic capacity under warm rearing conditions may reduce disease tolerance ( Lapointe et al, 2014 ; Bruneaux et al, 2017 ), increase risk of predation ( McInturf et al, 2022 ) and indicates that despite maintaining aerobic performance at temperatures exceeding 23°C, juvenile Chinook Salmon remain cold-water fish. We were only able to include fish that survived the metabolic trials, and fish exposed to temperatures exceeding 23°C often succumbed to heat stress during the RMR ( Supplementary Table S1 ) Therefore, our metabolic estimates of juvenile Chinook Salmon at warm temperatures may overestimate the true performance, as less thermally robust fish could not be represented.…”

Effects of acclimation temperature and feed restriction on the metabolic performance of green sturgeon

“…Additionally, temperature has an influence on the swimming capacity of juvenile sturgeon ( Allen et al., 2006 ; Deslauriers and Kieffer, 2012 ). Changes in the relative performance in swimming capacity have been linked to changes in trophic interactions between largemouth bass and juvenile Chinook salmon ( McInturf et al., 2022 ), and should be expected that artificially cold temperatures may influence the biotic interactions among green sturgeon and their environment. Therefore, reconciling the conservation conflict between green sturgeon and Sacramento River winter-run Chinook salmon will require understanding the effect of temperature on both organism physiology and its ecology.…”

“…Temperature plays a fundamental role in the biology of organisms across biological scales ( Brett, 1952 ; Hochachka and Somero, 1968 , 2002 ). Despite the widespread acknowledgement of temperature’s importance, we are still making strides in understanding the interaction of temperature, physiology and biological communities ( Zillig et al., 2021 ; Brownscombe et al., 2022 ; McInturf et al., 2022 ). Rapid environmental change, whether through local anthropogenic forces or global climate change, will undoubtedly alter the temperature dynamics of ecosystems.…”

“…Aerobic metabolism is a wholistic physiological trait that integrates multiple aspects of thermal physiology (e.g. oxygen uptake, energy catabolism) and is relevant to organism growth, swimming performance ( Fry, 1947 ; Brett, 1971 ; Pörtner and Farrell, 2008 ) and potential ecological dynamics such as predation and foraging ( Brownscombe et al., 2022 ; McInturf et al., 2022 ). A higher aerobic scope (AS) value is theorized to facilitate greater fitness and conditions that reduce an organism’s aerobic capacity are considered detrimental ( Farrell, 2016 ).…”

Diets of Native and Non-Native Piscivores in the Stanislaus River, California, Under Contrasting Hydrologic Conditions

“…Alternatively, high and variable spring discharge has been associated with improved survival and recruitment of juvenile Chinook Salmon (e.g., Zeug et al 2014;Michel et al 2015;Michel 2019), presumably as a result of reduced predation. Increased water velocity, turbidity, and decreased water temperature-typically associated with higher discharge-are conditions considered to reduce predation on juvenile salmon (Gregory and Levings 1998;Michel et al 2020;McInturf et al 2022).…”