Several hundred dead salmon were found floating in the Buskin River over the weekend, the culmination of several naturally occurring factors, according to fish and game officials.
Experts from the Alaska Department of Fish and Game said the die-off was the result of a combination of natural causes, such as low water levels, high water temperature and the large number of salmon that had passed the Buskin weir the previous day.
“The Buskin has about double the 10-year average for pink salmon escapement,” said Tyler Polum, a fisheries biologist with the department.
Fish and Game data showed that 75,000 fish have passed the weir so far this year up to Sunday, compared to 20,000 the year before and nearly 40,000 in 2018.
From 2011 to 2017, the number of salmon that passed the weir ranged from 5,000 to 15,000.
Local management experts were notified about the die-off by a Kodiak resident who saw hundreds of dead salmon floating belly up, as well as foam in the Buskin River on Friday.
Polum said that on Friday alone, 22,000 fish passed the weir. High temperatures and low water levels led to low dissolved oxygen levels in the water, likely suffocating the fish.
The department found that the water temperature reached 65 degrees Fahrenheit over the weekend, which is 5 to 10 degrees above normal for the area, he said.
The foam was seen near a construction site where the U.S. Coast Guard is replacing a waterline near the Rezanof Bridge along Anton Larsen Bay Road.
Polum said the foam is a natural occurrence caused by bacteria eating carcasses in the river, and is not likely to be a byproduct from the construction project.
The Coast Guard is replacing the waterline they use for drawing water out of Buskin Lake to be treated and distributed to areas around the Coast Guard base and the airport, said Fish and Game habitat biologist Will Frost.
He said the Coast Guard is complying with their permit, which requires them to discharge the water in upland locations to avoid polluting salmon streams.
The dead fish appeared to be pre-spawn pinks and were mostly located upriver from the construction area, Polum said, but added that his team did not observe the entire length of the river.
Similar phenomena occurred in 2018 and 2019, primarily in rivers other than the Buskin, such as the Olds River. With last year’s record heat and low water levels, large numbers of dead fish were seen in many of the local rivers.
Experts from multiple agencies collaborated to find the cause of the die-off, including the Alaska Department of Fish and Game, the agency that manages Kodiak’s fisheries; the Sun’aq Tribe of Kodiak, which keeps a close eye on the Buskin because of its importance for subsistence fishing; and the U.S. Coast Guard Environmental Division.
This summer, scientists have reported higher-than-average water temperatures in the Gulf of Alaska, which is known to impact the ocean’s fish populations.
In addition, Kodiak has seen another dry year with rainfall far below average.
A record high temperature of 76 degrees Fahrenheit was set on Friday, according to the National Weather Service. This broke the old record of 72 degrees set in 1953.
“If we don’t get rain, it could happen again both here in the Buskin, and elsewhere around Kodiak,” Matthew Van Daele, a tribal biologist with the Sun'aq Tribe, said about the salmon die-offs.
He said that with little rain forecast for the near future, he is concerned about the Buskin coho salmon, which are highly sought after by sport-fishing and subsistence users because of their economic importance.