Energy Depletion and Stress Levels in Sockeye Salmon Migrating at the Northern Edge of their Distribution

Abstract

The physiological challenge for anadromous fish to migrate upriver is influenced by river temperature, but the impacts of river temperature can be difficult to predict due to an incomplete understanding of how temperature influences migration costs, especially in high‐latitude (>60°N) ecosystems. To assess temperature influences on migrating Pacific salmon Oncorhynchus spp., we measured heat shock protein 70 (HSP70), as an indicator of cellular stress, and energy content of Sockeye Salmon Oncorhynchus nerka throughout their upriver migration in the Pilgrim River, Alaska. Although HSP70 was elevated as fish moved to the spawning grounds and was higher in fish with low energy content, HSP70 did not increase with warmer river temperatures. We verified in an experiment that HSP70 abundance in Sockeye Salmon does respond to temperatures above 20.5°C. Over the 4 years of sampling, energy content decreased at similar rates as Sockeye Salmon moved upstream. We expected Sockeye Salmon energy levels would be lower when migrating in warmer river temperatures; however, we found higher energy levels occurred with higher temperatures in the Pilgrim River. We hypothesize that the relationship between temperature and energy content is due to river temperatures often occurring below optimal temperatures for migration. Lower temperatures could be energetically costly or reduce migration rates, both of which would result in lower energy content with cooler temperature. Understanding interactions between environmental drivers and physiological responses will help managers anticipate future changes for Sockeye Salmon at the northern edge of their distribution.

Step-patterned survivorship curves: Mortality and loss of equilibrium responses to high temperature and food restriction in juvenile rainbow trout (Oncorhynchus mykiss)

“…Our hypothesis that individuals dying late in the challenge predominantly due to starvation and caused by a lack of food resources has strong support in the literature. The energy density critical thresholds of 4.0 kJ�g -1 at mortality and 4.3 kJ�g -1 at LOE are similar to 4 MJ�kg -1 observed in migrating adult sockeye salmon [11,54,55]. Although, lower values (2.9 kJ�g -1 ) have been observed in adult sockeye salmon at time of mortality [56].…”

“…Differences within species adapted to different thermal environments can vary more widely than between species adapted to the same environment [75]. In a study of salmon in the wild, there was large variation in hsp70 levels on the spawning grounds [55]. Interestingly, individuals with higher hsp70 levels, that were induced by means of any kind, had lower energetic content than the rest of the individuals.…”

Evidence of prevalent heat stress in Yukon River Chinook salmon

“…In addition to thermal stress, heat stress biomarkers can be induced by a variety of environmental factors (Deane and Woo 2011), including social stressors and lack of food (Currie et al 2010). In our studies, the wide variation in heat stress rates between study years within locations provided additional confidence that heat stress classifications were robust to changes in gene transcription and HSP70 protein during the spawning migration that are associated freshwater entry, sexual maturation, and senescence (Evans et al 2011;Miller et al 2011;Carey et al 2019). Our sampling focused on collections that occurred in migration corridors and used only live fish sampled within minutes of capture.…”

Technical fishway passage structures provide high passage efficiency and effective passage for adult Pacific salmonids at eight large dams

“…For example, genetic stock identification and identification via parentage-based tagging [e.g., 46 , 68 ] of future telemetered fish would dramatically reduce the uncertainties associated with fish origin. Collection of additional fish trait and risk data, including physiological or transcriptomic measures of energetic status [e.g., 117 , 118 ], pathogen burden [e.g., 119 , 120 ], or stress indicators [e.g., 103 , 121 , 122 ], and quantification of individual thermal experience [e.g., 41 , 46 , 122 ] or activity budgets [ 123 ], would likely yield important insights on fish behaviors at the dams and on passage failure mechanisms. Tagging and monitoring individual fish has proven effective for assessing migration survival questions over large geographic areas [e.g., 124 – 126 ], but passive monitoring methods can also provide insight on failure mechanisms.…”