Salmon is economically and commercially important to the state of Alaska, but recent heat has led to some concerning factors. With temperatures soaring well above record values, many streams and rivers that are not glacially fed are exceeding safe levels for salmon.

A release from the Cook Inletkeeper highlights just how warm waters have been, with one river rising to a temperature level never seen.

The Deshka River, which is a major salmon stream on the west side of the Cook Inlet, topped out at 81.7 degrees Fahrenheit. It was the warmest stream temperature recorded since 2002, when the Cook Inletkeeper starting tracking stream temperatures.

While waters do warm during the summer months, Sue Mauger who is the Cook Inletkeeper's science director, said stream temperatures have never been measured above 76 degrees Fahrenheit. 

This heat is leading to thermal stress in salmon and preventing them from migrating upriver. Data from the Alaska Department of Fish and Game shows that only 13 chinook salmon passed the Deshka weir from July 1–9.

Temperatures above 80 degrees Fahrenheit are not just stressful on salmon, but lethal, which is blocking the migratory corridors for salmon on their way upstream. With temperatures above 70 degrees Fahrenheit, salmon are holding in the lower river, waiting for cooler nighttime temperatures or rain to help cool the river.

Outside of the past few days, temperatures have struggled to fall below that threshold, likely preventing most of the salmon from migrating upstream, hence the low number that passed the Deshka weir. 

The heat is a growing problem for salmon not only in Alaska, but in the Lower 48 where it's already taken a toll on them. This can effectively disrupt the ecological cycle, as many wildlife depend on the salmon to survive. The focus now, according to the release, is how tolerant are salmon in Alaska and how effective they might be in finding patches of cold water to ride out warm spells. 

The Deshka River is not only a major salmon stream, but is one of the most important salmon streams in Southcentral Alaska. With warming temperatures and water that can be lethal to the salmon, there is some concern for how the current climate crisis is impacting salmon.

We're already seeing the effects of lower escapement along the river. The Inletkeeper states that 13,000–28,000 salmon is the escapement goal each year, but only two of the last five years saw that meet or fall within that criteria. 

 

Deska River Chinook salmon escapement from 2015-2019 (Photo: ADFG)

The heat over the recent years has also led to declining numbers of salmon in other areas of the state. The US Geological Survey has been studying chinook salmon in the Arctic-Yukon-Kuskokwim region and have seen a decline to low numbers.

This prompted several disaster declarations by the state and federal government, as the drop in numbers could affect local fisheries and economies. As salmon respond to the warmer temperatures in water, the heat stress is leading salmon to exhibit heat shock proteins and express certain genes. Studies are still being done in just how the salmon respond to these warm temperatures. 

One study published in the G3: Genes, Genomes, Genetics journal points to the effects that temperatures can have on fish species worldwide.

Young chinook salmon have been documented as seeing an increased likelihood that warm water will negatively impact survival, growth, and development. The warmer waters also pose a threat to a dwindling salmon population, due to changes in ocean and climatic conditions.

However, genetics can also play a huge role in how individual salmon respond to altered stream temperature variations. The United States Department of Agriculture states that stream temperature variability matters to salmon in its natural state, but when factoring in the current climate crisis and human activities, the nature variability is altered.

Outside of warm water causing stress to salmon, it also holds less dissolved oxygen than cool water, which is not good for the survival of aquatic life. This is especially true for salmon, which require clean, oxygenated water to survive. 

So what can be done in a warming environment with a declining salmon species?

Currently, the Cook Inletkeeper is in the middle of a five-year effort to map the variability of temperatures within the Deshka River. The goal is to identify where colder water persists, so that targeted conservation actions can be implemented to protect key habitats for the salmon.

With this year likely to close as one of the lowest escapement goals for chinook salmon in several years, these steps will likely build resilience for the salmon as the climate continues to change. 

In order to help Alaska's salmon and the communities that rely on them, the Inletkeeper points to the stopped development of oil and gas projects and shifting to low or no carbon energy solutions. If not, the current climate crisis will not only send stream temperatures into unprecedented territory in the future, but will be a glimpse of what is to come if we continue to rely on fossil fuels.

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