Study monitors streams for changes in temperature

Homer’s Cook Inletkeeper is monitoring a number of streams in the Cook Inlet watershed for temperature and finding some troubling results, according to a newly released paper in the Canadian Journal of Fisheries and Aquatic Sciences.

Inletkeeper’s science director, Sue Mauger, said that the study looked at 48 different streams, and that continuous monitoring is happening at 17 streams around the Cook Inlet basin.

Mauger said the study is important to figuring out how a warming climate might affect salmon returns in Cook Inlet and Alaska in general.

“It’s a really good index to understand how climate might be altering the thermal condition of rivers, and for salmon, which are cold-water fish. They like temperatures that are below 55 degrees.

“It’s important to know where streams are changing and becoming more stressful,” she said.

Adult salmon are more tolerant to warmer temperatures; when they are smaller, or if they are in the egg stage or just emerging, they are less tolerant.

“Generally they’re happy when they’re below 55 degrees; 42-55 is optimal, above 55 is more stressful, and above 70 degrees can be lethal,” Mauger said. “We have measured temperatures in streams like the Deshka River where we’ve got temperatures that are about 76 degrees.”

The Deshka River in Upper Cook Inlet has been an important king salmon stream for many years, but has seen a crash in recent years.

Inletkeeper measured temperatures in 2004, 2009 and 2016, and found they were above 75 degrees.

Temperatures above 80 degrees increase chronic stress for salmon, making them more susceptible to predation, plus chemicals in the water become more and more toxic at high temperatures, so things like copper and mercury become more toxic the warmer the water is.

Warmer temperatures also make salmon more susceptible to disease, make it more difficult for them to put on weight, and force them to work harder to maintain their respiratory system.

“The Deshka River is the warmest of the rivers that we’ve measured in Cook Inlet, and there are rivers that are quite cold and should remain cold for a long time, but it’s really important to understand how these rivers are changing,” Mauger said.

“A system like the Deshka, in 50 years, might not be a reliable chinook system, and it might be on a much shorter time scale than 50 years,” Mauger said.

It is not just in-river temps affecting salmon populations. Mauger said that a system like the Deshka will become more regularly very warm, and increasingly warmer.

“What that means for a cold-water fish population is increasing stress, and there’s a lot of other factors that play into how a cold-water fish population is affected. especially salmon, because they’re experiencing a marine system, over the last five years, with a big thermal ‘blob’ of warm water in the Gulf of Alaska.”

Mauger said it is difficult to predict what is going to happen to the population level, but she can say that the thermal conditions are going to become increasingly stressful for cold-water fish.

She said that’s why it is important to establish the big networks of monitoring stream temperatures so that scientists can understand how many of the systems within Cook Inlet, and around the state of Alaska, are compromised.

“Is it going to be a third of the systems that are going to be too warm, half of them, only five percent of them? It helps you think about what the future of that fishery might be,” she said.

A similar system is being set up in Bristol Bay, and Mauger just returned from a trip to Southeast Alaska to discuss a future project there.

One thing Cook Inlet does have going for it is that the major driver of the sockeye and king salmon fisheries, the Kenai River, is glacier-fed and not quite as susceptible to warming temperatures.

“A glacial system is going to be colder for awhile as we have increased snow melt or glacial melt to that system,” she said.

“The work that we’ve done has not been in glacial systems, but the expectation is that the main stem of the Kenai River will see more glacial melt, which will also carry more sediment into the system, and then the non-glacial tributaries. Our study actually looked at seven of those. Some of those tributaries are quite warm, and some of them are quite cold. And so the fish may change their behavior and seek out some of those (colder) tributaries in the future,” Mauger said.

While salmon are largely hard-wired to return to their stream of birth, there has been evidence in the Pacific Northwest of fish honing in on cooler locations up and down the stream.

It may be that those tributary junctions become more important places for them before they make a last dash up to where they are going to spawn, or it may be that the fish that use those cooler spawning areas are more productive, and that the bulk of the population is supported by the fish that use those cooler locations.

According to the study, climate change is happening fastest in northern latitudes. The study focused on understanding rates and drivers of changing temperature regimes in Southcentral Alaska streams, and implications for salmon populations.

It collected continuous water and air temperature data during open-water periods from 2008 to 2012 in 48 non-glacial streams across the Cook Inlet basin spanning a range of watershed characteristics.

It found that the most important predictors of maximum temperatures were elevation and wetland cover, while thermal sensitivity (slope of stream-air temperature relationship), was best explained by mean elevation and area.

It found that the maximum weekly maximum temperature at most sites exceeded established criterion for spawning and incubation, 55 degrees, above which chronic and sub-lethal effects become likely.

This happened every year of the study, which suggests salmon are already experiencing thermal stress.

Projections of those temperatures over the next 50 years suggest these criteria will be exceeded at more sites and by increasing margins.

Find the full study at

Cristy Fry can be reached at