Cook Inlet streams' record high temperatures could be fatal for salmon

Jul 11, 2019

King salmon
Credit Photo KBBI.

A dry heat wave across Southcentral Alaska has raised temperatures in Cook Inlet streams, and there’s fear the sunny weather and warm water could be bad news for salmon.

Sue Mauger has tracked non-glacier stream temperatures in Cook Inlet for years. And she says she hasn’t seen readings like these.

“We saw the highest recorded temperature we've ever measured in 15, 16 years,” she said. “That was 81.7 degrees on the Deshka River.”

That’s a north-south river between Talkeetna and Anchorage known for its premier sportfishing.

“So really, so far beyond what is comfortable for salmon and also at least five degrees warmer than any [recorded temperature] previously,” she said.

Mauger is the science director for Cook Inletkeeper, a Homer-based conservation group. She said the waters of the Deshka usually peak in the low 70s. But this year, it was different. And it’s not alone: the Anchor River on the Kenai Peninsula broke previous records at 73 degrees. 

These temperatures might be great for bathing. But it can doom Alaska salmon.

“Certainly once you get into those high seventies and eighties, those are known to be lethal temperatures for salmon—they're really cold water fish,” she said.  

So far there haven’t been any die-offs reported. That suggests the fish have been able to find pockets of cold water to survive. 

Mauger’s also worried about the incredibly low returns to date.

The Alaska Department of Fish and Game recorded just 13 chinook past the Deshka Weir in the first nine days of July. This, in a river that produces chinook - or king salmon - in the tens of thousands. 

Fish and Game Area Management Biologist Glenn Hollowell notes it’s not just warm water in Cook Inlet streams that concerns him. It’s also low water levels.

“When we're flying aerial surveys, we look down and go, wow, normally there's three feet of water there and we're seeing half that or less,” he said.

But he’s says fisheries managers feel it’s too early to write off this season’s salmon.

“The summer's not over yet,” he said. “Actually the goals that we've gotten in hand right now are looking pretty good for escapement, but I'm going to be very concerned if we get another month of very sunny weather. I think that could be impacting a lot of our returning stocks then.”

What’s needed, he said, is rain. And there is some in the forecast along with cooler weather. But if that cool rain doesn’t come soon, he said, the salmon returning from Cook Inlet could suffer.