In the first of a two-part series, we explored the effects of warming river water on salmon. Now we take a look at the warming ocean, and what that means to the Yukon River king run.
Managers have noticed that in recent years, smaller, younger king salmon are returning to salmon streams. Since these changes are occurring statewide, and the fish spend most of their lives in the ocean, researchers think that this trend has something to do with changes in the marine environment. In the Bering Sea, that includes such factors as the loss of the “cold pool” of ocean water that once was thought to have helped nurture cod, and the loss of sea ice. Both are major changes in where fish species are located: their habitat.
“That’s the same habitat that these Chinook salmon are in during their entire marine life,” said Katherine Howard.
Howard is a state fish biologist doing high-seas salmon research. She studies juvenile salmon caught in the fall ocean trawl surveys operated by the National Oceanic and Atmospheric Association in the Bering Sea.
“And the Chinooks that are caught are primarily 2-year-old fish,” says Howard. “So we are really monitoring a cohort of fish.”
Using genetic information from the catch, Howard was able to figure out how many of the fish were Yukon River Chinooks, otherwise known as king salmon. Her team found a direct relationship between the number of juveniles and the number of kings returning to the Yukon three years later. That means that the trawl data can be used to project into the future.
“Typically, with salmon forecasts you’re only looking at the next season,” she said. “But we’re looking three years out, because we’re looking at juveniles, and these fish are staying in the ocean for an additional three years.”
In warmer oceans, biologists are seeing faster growth and they’re seeing younger fish returning earlier. Howard wondered if they would find the same trend of increasing growth in the juvenile kings in her trawl survey.
“Sure enough, we see exactly the same thing,” Howard said.
Howard says that the trawl data also reveals changes in the diets of the kings. The changes are so fundamental that right now there are more questions than answers.
“We don’t know what that is going to mean in terms of survival and productivity of these stocks until those fish return to the river,” Howard explained.
What she does know is not good news for the Yukon. Based on her data, she expects some small runs ahead, especially in 2022. Howard expects runs similar to those seen in 2012 and 2013.
“These weren’t good years,” she noted. “These were years when even if no fish were harvested in the river, we would still have struggled to make escapement objectives.”
The only good change she sees is in the people fishing on the Yukon. Howard told a room full of scientists that the attitudes of the people along the river have changed. In the past, she said, people were trying to get more fish for themselves. Now, she observes that the conversation has turned to conserving and protecting the Yukon king run.