Salmon are an iconic species group in the Pacific northwest. They act as both predator and prey, and their presence is vital to many species, most notably, the endangered southern resident orca. Pacific salmon make up 90% of the diet of a southern resident orca (80% of which is Chinook), and the protection of the orca depends on the preservation of the salmon.
Pacific salmon are incredibly sensitive to changes in their habitats, making it exceptionally challenging for them survive in a world increasingly impacted by climate change and human activities. Pacific salmon populations have changed drastically since the early days of industrial fishing. Though fisheries still do influence salmon populations, there are many other obstacles in their path, such as dams and habitat destruction (Discussed in Part 1 of the salmon story found here). This post will focus on the impact of climate change and a warming ocean.
Salmon are ectotherms, meaning they are unable to regulate their body temperature when their environment changes. As the Earth continues to warm, so do the oceans, and salmon may not have the tools to handle that. Studies show that in years when we experience warmer ocean temperatures, there is a decrease in the return of adult salmon.
Warming oceans impact salmon from several directions. Temperatures above 18°C seem to decrease the swimming performance of adult salmon. Temperatures above 20°C may reduce salmon egg viability and can cause fatalities in adult salmon before spawning. A warm environment also increases the metabolic rate of the salmon, meaning they need to eat more food. Warmer water is less productive, so the food may not be as easy to come by.
Additionally, years with higher ocean temperatures cause a shift in the way prey are distributed. Salmon usually exist in ecosystems with fatty zooplankton, allowing them to get more bang for their buck while feeding. During warmer years, these ecosystems must survive on less fatty zooplankton that have shifted from southern waters. This means salmon eat more food, but are smaller, and have a poorer body condition than years with cooler oceans. Being smaller for longer makes juvenile salmon more vulnerable to predators due to their decreased size, and the longer period spent in the open searching for food.
How to Help
What can we do to help salmon survive while ocean temperatures continue to rise? Start by limiting your salmon consumption and by buying sustainably harvested salmon whenever possible. Participate with organizations that have dedicated themselves to saving the salmon such as the Pacific Salmon Foundation and Pacific Wild. Keep educating yourself and those around you and spread the word that our salmon need help. Finally, do your best to shrink your carbon footprint. Ultimately, fewer greenhouse gas emissions will be the most important part of keeping our oceans and rivers cool enough for salmon to chill in, and the fridge well-stocked with Chinook for the orca.
If you’d like to learn more about obstacles facing Pacific salmon, check out Part 1 of this post.
Grant, S. C. H., MacDonald, B. L. & Winston, M. L. 2019. State of Canadian Pacific salmon: Responses to changing climate and habitats. Fisheries and Oceans Canada Science Branch, Pacific Region. Retrieved from https://waves-vagues.dfo-mpo.gc.ca/Library/40807071.pdf
Daly, E. A. & Brodeur, R. D. 2015. Warming ocean conditions relate to increased trophic requirements of threatened and endangered salmon. PLoS ONE 10(12), 1-23.
Feature Photo taken by: Valérie Messier