Physiological and Environmental Factors Influencing Pacific Salmon Fitness in a Changing Climate

Alexander T. Iritani

doi:10.7273/000007391

Pacific salmon are becoming increasingly threatened by the impacts of climate change, but because each species exhibits different life history strategies, their adaptive capacities may vary. In the marine environment, sea surface temperatures are increasing by 2-4 degrees C°, ocean currents are shifting, and carbon dioxide absorption rates are increasing. Cumulatively, these marine shifts are impacting thermal regimes which drive primary productivity, and the dynamics of predator-prey interactions, while Carbon Dioxide absorption is leading to deterioration of the outer shell of plankton and benthos species, both of which are important food sources for salmon. Similarly, in the freshwater environment, changes in climate regimes are driving earlier peak stream flow, increasing water temperatures, and creating more hypoxic river and lake conditions. The factors which contribute to the resilience of the fish to shifts in both marine and freshwater environments are generally split into four categories- metabolism, hormonal, behavior, and the immune response. Cumulatively, the plasticity in these important physiological mechanisms provides buffer to both natural and anthropogenic stressors. Many of these are not well understood, particularly across different salmon species. In this thesis, the metabolic rate and egg size of two different Pacific salmon embryos is analyzed to provide further insight into the critical developmental period which often experiences high mortality. Our findings show that the mothers genetic effect contributes most to metabolism early on in development, and towards hatching both maternal and paternal contribution are more evenly distributed, and while egg size may have some effect on metabolic rate, it is not the main contributor in our study. Another main contributor to salmon health and resilience is the microbial community within the innate immune system which functions to provide as a host for symbiotic bacteria and keep out pathogens. We analyzed the mucus of three different salmonid species to characterize microbiome communities within the mucus in the adult migration. Our findings showed that microbiome communities differ in geographically distinct populations of the coho salmon, and that in our sockeye and steelhead populations, the microbiome may be relatively well-equipped to keep out bacteria from the environment early on in, although it was evident that shifts in the microbiome seemed to be associated with environmental and morphological changes in salmon close to spawning. Additionally, evidence showed that marine derived bacteria are being transported via the fishes mucus. Our findings provide insight into the important physiological mechanisms which influence salmon health and the adaptive capacity to environmental stressors.

Physiological and Environmental Factors Influencing Pacific Salmon Fitness in a Changing Climate

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