in june 2021, a heat wave spread over the pacific northwest, from northern california up into british columbia, with people in the region wilting from record high temperatures in excess of 100 degrees fahrenheit and facing greater threats of wildfires. but the threats are soaring for rivers and marine life as well. 

rivers in the region saw water temperatures reach levels lethal to salmon, leading to mass die-off of many species already in decline. the decimation continues for one of the most culturally and economically crucial species in the region. 

“we’re going to lose very important runs of salmon in the next 20 years,” said colleen weiler of whale and dolphin conservation. “they’re just going to be gone because the water is going to be too hot.”

the acute impacts of heat waves on wildlife in the region is severe, and in particular for stocks of pacific salmon. with global air and water temperatures rising due to climate change, the heat wave provides an insight into the long-term effects on these populations. the damage of a mere one degree centigrade of global temperature rise is already evident. the paris agreement, an international treaty on curbing climate change, commits participating countries to rein in temperature rise to 1.5 degrees, and predicts far more catastrophic effects if temperatures rise to 2 degrees. 

salmon and climate change 

the complex biology of salmon means they spend different stages of life in different habitats. juveniles can spend up to three years in freshwater stream systems before making their way to the ocean in the spring. once they reach maturity, the salmon return from the ocean to their birth stream to spawn. in these freshwater streams, the effects of climate change are having the biggest impact and threatening the spawning environments.

“it has a lower heat capacity,” said emmie page of pacific wild. “it’s going to increase the temperature at a greater rate than in comparison to the ocean, so those freshwater juveniles are going to feel that temperature much more.”

andrew trites, of the institute for the oceans and fisheries at the university of british columbia, said these juveniles are often overlooked, and that there is more to the life cycle of salmon than the number of adults. he said the small, juvenile, fish are very important to the food web as lots of species depend on them as a food source. 

“it’s very much a human view about fish,” he said. “it’s all about how big of a fish can we catch, and can we catch enough?”

as a cold-water species salmon are sensitive to changes in water temperature, and trites said that to a fish, a degree-and-a-half increase in temperature will have huge impacts. 

“it increases their metabolism,” he said. “they breathe heavier or faster in warmer water, which means that they need to eat more food because their metabolism is ramped up.”

page added that salmon take their biological cues from these seasonal temperature changes.

“there might not be the correct biological cues for them to migrate at a certain time because of the earlier changes in temperature,” she said. 

adult salmon of each species spend different cycles of time in the ocean before migrating back to their birth streams to spawn, page said. the changes in temperature could therefore also impact the timings of the returning mature salmon runs in the autumn months. 

trites added that large numbers of pink salmon come back every two years, so the population is regularly replenished. 

“then you’ve got others, like the chinook salmon, which come back somewhere between three, five, and even six years,” he said. “they’ve got a very complicated life history.”

each species supports different conservation units, and each of these is given a different classification of protection. under the endangered species act, a population at risk of extinction throughout all or a significant portion of its range will be listed as endangered. if a population is considered likely to become endangered in the near future, it will be listed as threatened. 

according to the national oceanic and atmospheric administration, none of the alaskan salmon stocks are classified under the act but multiple west coast stocks are. 

“i think people kind of lost that awareness of their endangered status and where salmon comes from,” weiler said. 

of the five pacific salmon species, pink salmon are most abundant and not listed for protection; and chinook salmon is the most at risk, with two populations listed as endangered and seven as threatened.

this, along with the differences in biological cycle between pacific salmon species, makes imposing protections on salmon difficult and nuanced.

“they’re the same species as one another,” page said. “but they have different migration patterns, different home streams, spawning grounds. it’s going to take such a long time to navigate every single conservation unit and what it’s going to look like in a couple years.”

the increasing global temperatures are also impacting annual snowmelt which, in turn, impacts the salmon. 

“the most common thought is that, with the heat, it’s caused early snowmelt,” said page. “by the time it comes for their migration back to their home spawning streams, the water’s going to be way too hot, maybe even almost lethal temperatures for them, and way too shallow and way too dry. to the point where they won’t even be able to swim up those streams.”

trites said salmon populations in the south will likely disappear first, that in addition to the warming water temperatures the added pressure of rivers being dammed is severely impacting the populations. 

“with climate change happening the prognosis for salmon, particularly chinook salmon, is very bad,” he said.

impacts to southern resident orca

in addition to their importance in human diets and heritage, salmon play a critical role in the chain of marine life. 

the endangered southern resident orca population feeds predominantly on salmon, chinook salmon in particular make up over 50% of their diet. declines in vital salmon stocks that pass through their boundaries, as well as the presence of organic pollutants in the water and noise disturbance from vessels, is commonly attributed to the loss in numbers. 

weiler said the southern resident orca rely on different salmon populations at different times of the year, so no one river system can be prioritized as a panacea for orca issues. 

“it’s not like we can just save one river, call it good, and the whales could eat on that year-round,” she said. “they need fraser river salmon, which is in canada, in the summertime, and they need snake river salmon in spring.” 

proposals are being made to consider the southern residents as more than just predators when determining the yearly salmon fishery quota. 

“they are such salmon specialists,” said weiler. “they really should be included as another stakeholder and given their own quota of fish.”

weiler said it is a complicated area of political pressure. as a trans-boundary species, protection of pacific salmon and quotas are established by both the u.s and canadian governments, at the state level and also by the different tribal and first nations governments. 

“it’s a lot of finger-pointing,” she said. “everybody blames whoever’s not in the room for taking more salmon than they should, and a lot of times that ends up being whales, and seals and sealions.”

trites added that sometimes you can protect threatened populations while still fishing for abundant ones, and sometimes you can’t.  

“it’s not a job i would want because you upset lots of people,” he said. “no matter what you decide.” 

southern resident orca habitat extends from southern british columbia, canada, down to california. 

noaa announced on july 30, that designated critical habitat for southern residents will be extended from the inland waters of washington state to include coastal waters through monterey bay. the expansion will add an additional 15,910 square miles to the existing habitat, and according to weiler it took seven years to implement the ruling.

non-climate related impacts

salmon are a staple in the pacific northwest. not only are they a food source to both humans and wildlife but they are important in ceremonial traditions within the indigenous communities both on the coast and inland. 

julian matthews of nimíipuu protecting the environment, and a member of the nez perce tribe, said salmon in idaho’s clearwater river have been declining for a number of years. 

“fifteen to 20 years ago we could go down and grab a couple, or grab 10 to 20,” he said. “but now it’s so limited that i didn’t even go this year, it’s not worth it because there’s no salmon coming up.”

the clearwater river joins the snake river at the idaho-washington border, and both make up part of the columbia river basin. in addition to rising water temperatures, salmon populations in freshwater rivers are impacted by hydroelectric dams. 

according to the u.s. army corps of engineers there are 18 dams along the columbia and snake rivers, with eight of these impacting pacific salmon migrations. 

“we feel that the dams need to be breached or removed,” said matthews. “to allow for better movement up and down the river.”

idaho congressman mike simpson recently announced a new salmon recovery and habitat restoration initiative that involves the removal of the four lower snake river dams. 

“a concept like this will take all the northwest delegation, governors, tribes and stakeholders working together to draft a solution,” simpson said in a statement online. 

weiler said the removal of the snake river dams is something conservation groups have been advocating, as it links to the recovery of prey in southern residents’ coastal range. 

“it’s a very complicated and controversial topic,” she said. “pretty much any time you talk about major dam removal, it is very tricky. but there has been some really good forward movement this past year.”

looking to the future 

as well as simpson’s proposal, the canadian government has recently announced its new pacific salmon strategy initiative, allocating just over (cad) $647 million to salmon research and restoration projects. 

page said the funding will allow for more extensive data collection, particularly of remote, northern salmon stocks.

“we need proper numeration; we need to know what the populations actually look like,” she said. 

trites said salmons’ ability to adapt is how they entered different river systems in the first place, and that it’s difficult to know exactly how they may adapt to the environmental changes they’re faced with. he said it could be a case that some rivers further north that don’t currently support salmon stocks may become suitable in the future. 

“i don’t think any of us know for sure what the final system will look like,” he said. “climate change is the huge unknown.”