Hundreds of salmon found dead in Kodiak
Die-offs of salmon before they spawn are becoming more frequent. Here’s why:
ANCHORAGE, Alaska (KTUU) - Over the weekend, Kodiak residents began to notice numerous dead pink salmon in a river popular with fishermen. The Buskin River, located near the Kodiak Airport and a short drive from town, is known for its sockeye and silver salmon runs.
This season, there was a large pink salmon run up the Buskin River, but many were found belly up having died before spawning. Some residents wondered if it was related to a nearby construction site, but Tyler Polum, the Kodiak sportfish biologist with Alaska Department of Fish and Game, said the cause was part of a larger trend seen around the state.
“It looks really consistent with what’s happened the last couple of years in various rivers around here and other places in the state,” Polum said.
The Buskin River was warmer than usual with water around 60 to 65 degrees. Warm water cannot hold as much oxygen as colder water. That, combined with low water levels, reduced the number of fish the river could support.
“It’s pretty likely that the dissolved oxygen in the water just got so low that they died of suffocation basically,” Polum said.
Kodiak Fish and Game observed several hundred fish — mostly pink salmon with some silver salmon, rainbow trout and Dolly Varden mixed in — dead in the river.
Polum says around 75,000 pink salmon have returned to the Buskin River this season so far, but the low water level has created a situation where the numerous salmon are depleting the already limited oxygen in portions of the river.
August in Kodiak is normally one of the drier months of the year, but meteorologist Kaitlyn O’Brien said this August has seen less rainfall than usual by almost an inch and a half.
“There is a notable decrease in precipitation specifically in what we would normally see in the month of August,” O’Brien said.
Across the island, rivers are exhibiting conditions that lead to salmon mortality, Polum said. In 2018 and 2019, the high water temperature, low water level and low dissolved oxygen level resulted in more salmon deaths in the Buskin River and throughout the state.
Warming waters, warming planet
Last year was a particularly difficult year for salmon migrating up the Koyukuk River with at least 1,364 chum salmon found dead. Peter Westley, an associate professor at the University of Alaska Fairbanks, studied how the mortality of the chum salmon was related to the 2019 heatwave.
“All of these signs point to these types of events becoming more frequent and potentially of greater magnitude as things warm up,” Westley said. “So in some ways, it’s surprising when it happens, but I think we’re going to get to the point where we are not surprised.”
Alaskans are accustomed to watching salmon die each year. The rotting carcasses line river sides following a period of spawning. What’s not normal is finding dead salmon before they have spawned. Will heat stress deaths have an impact on future salmon counts?
“That’s the million-dollar question,” Westley said.
In places like the Buskin River, Polum said it could impact future sport fishing opportunity. The effect on salmon populations in the Koyukuk River, a major tributary of the Yukon River, is still unknown.
“There’s really not much good about fish dying en route to spawn, that’s for sure,” Westley said.
Brian Brettschneider, a research scientist with the National Weather Service, said Alaska has been “exceptionally warm” between 2015 and 2019, which mirrors a global trend where the last five years on record have also been the five warmest years.
“We are definitely, of course as everyone knows, warming up here in Alaska and that’s one of those cascading effects that people maybe didn’t use to think about but is more front and center now,” Brettschneider said.
This year is expected to finish as either the warmest or second warmest year on record, but Westley said there is still work that can be done to prevent heat stress deaths in salmon.
Since sockeye salmon migrating up the Fraser River in Canada started dying off over a decade ago, salmon mortality has been the focus of more research. In Alaska, Westley says there’s a growing movement to systematically store information on these deaths, catalog the magnitude of the deaths and sample the water temperature and oxygen level.
There are still ways to protect the habitat even in warming conditions. Some river areas are naturally cooler with groundwater tributaries often bringing in colder water.
“What we do have the control of is the protection of these habitats and allowing fish to find places in rivers, as much as possible, that might be refuge,” Westley said.
Some researchers say the full negative impacts of heat stress on salmon won’t be seen until the offspring return.
Copyright 2020 KTUU. All rights reserved.