Chinook Salmon: Responses to an Increasingly Hostile Environment

            As temperatures continue to rise around the world, due to global climate change, organisms are being forced to face new challenges that threaten their survival. These changes in the environment can have severe consequences for population dynamics and the distributions of organisms. This means that warming temperatures, that induce thermal stress in organisms, can cause changes in the size and age make-up of populations by altering factors such as mortality, growth, and behavior. Additionally, rising temperatures can change the distribution or spread of organisms in an area because higher temperatures may be more suitable for certain species and allow them to expand the range in which they are usually found, while higher temperatures may also cause thermal stress in other organisms and severely limit their survival and range. Many scientists have studied the ways in which organisms will respond to different facets of climate change, however, more research is needed to predict how multiple environmental stressors, that result from climate change, may affect organisms and ecosystems.

            One species that is already being affected by climate change and will continue to experience detrimental effects due to rising temperatures is Oncorhynchus tshawytscha, or Chinook salmon. Specifically, juvenile Chinook salmon, which are both economically and ecologically important in the western United States, are facing the dual threat of rising temperatures and invasive predation by smallmouth bass. Not only are rising temperatures inducing thermal stress in these young organisms, but they are also facilitating the migration of invasive smallmouth bass further upstream into juvenile salmon habitat. In order to study the “Costs of living for juvenile Chinook salmon in an increasingly warm and invaded world,” Dr. Lauren Kuehne and her colleagues studied the interactive effects of rising temperatures and smallmouth bass predation on mortality, behavior, physiology (or the normal function of living organisms), and growth (Kuehne et al. 2012).

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            In this study, the authors conducted 48-hour trials in artificial stream channels for four treatment groups: (i) warm+ predator (ii) warm+ no predator (iii) cool+ predator (iv) cool+ no predator. Kuehne et al. found that there was no increase in predation in warmer temperatures; however, they did find that the combined environmental stressors caused significant effects on the growth, physiology, and behavior of the juvenile salmon. More specifically, they found that salmon in the warm+ predator treatments showed the lowest growth compared to the other treatments. They also found that plasma glucose and plasma cortisol levels, which are commonly used to measure physiological stress responses in fish, were higher for the salmon in the warm and predator treatments compared to the reference treatment (cool+ no predator). Finally, they found that anti-predator behavior (such as swimming in groups and decreased swimming time) were highest in the warm+ predator treatment. Therefore, even though the combined stressors did not affect mortality (predation), these stressors are likely to have significant sub-lethal effects for juvenile salmon as climate change persists.

            The findings of Kuehne et al. add to current scientific knowledge, regarding climate change, by examining how an important and endangered species may be affected by the interaction of multiple environmental stressors brought on by the changing environment. This research has implications for the ways in which changing distributions of species and thermal stress will interact to impose sub-lethal constraints on organisms. These sub-lethal effects have harmful implications for salmon and will likely impact their growth and development, resistance to disease, and mortality in the longer term.  These effects could lead to changes in the population dynamics of Chinook salmon and more research is needed to find out what kind of long term effects these environmental stressors will have on ecologically and economically important juvenile salmon.

Reference:

Kuehne, L.M., Olden, J.D., Duda, J.J. Costs of living for juvenile Chinook salmon (Oncorhynchus tshawytscha) in an increasingly warming and invaded world. 2012. Canadian Journal of Fisheries & Aquatic Sciences 69(10): 1621-1630. doi:10.1139/f2012-094.