Environmental conditions are likely to have a significant impact on Yukon River chinook salmon, and it’s something fisheries managers should pay attention to, according to a new scientific paper.
The paper, published in the latest issue of the Canadian Journal of Fisheries and Aquatic Sciences, saw researchers extract decades of data on “environmental and ecosystem variables” such as water temperature, precipitation and ice melt history. Yukon River in Dawson City. They then looked at the possible effects of these variables on chinook at various stages of life, from eggs to migration of mature fish back to spawning grounds.
Lead author Alyssa Murdoch told CBC News in an interview that the effects were “not insignificant.”
“We were finding this on the scale of, you know, loss of about tens of thousands of fish,” he said.
Researchers found that wetter conditions, particularly in the Yukon River basin, can have a devastating effect on juvenile chinook; Less than three centimeters of additional rain could result in the loss of an average of 13,000 salmon.
This is because more rain means more water runoff, which can displace young fish and disrupt their feeding.
Murdoch also noted the finding that just a 1.2 C increase in water temperature in the Yukon River during chinook spawning migration could result in a reduction in fish numbers by an average of 12,000 fish.
“At extremely low returns, where every fish counts, twelve thousand salmon is actually quite a big number,” he said.
Chinook on the Yukon River have seen sharp declines in run sizes in recent years; 2022 and 2023 were the worst and second-worst runs on record, respectively. According to preliminary 2023 figures, only 58,529 chinook entered the mouth of the river in Alaska, with an estimated 14,752 reaching Canada; this number was only one-third of the number needed to meet the lower end of the spawning escape target.
Other environmental factors that researchers have found to have a negative impact on chinook include increased precipitation during spawning and egg incubation, warmer and longer springs and summers, and an increase in the number of pink salmon in the ocean.
Breaking of ice on the Yukon River at Dawson City at a later date could also have a negative impact; Researchers suggest that the longer the ice remains in place, the longer it will be delayed in reaching coastal areas and the ocean.
The findings on temperature and precipitation are particularly relevant because Yukon watersheds are expected to become warmer and wetter as the climate changes, the paper said.
Warmer water could be positive in some cases, researchers say
But Murdoch said researchers have found that chinook are “very complex” and that in some cases environmental changes can actually have a positive effect.
For example, warmer water during spawning and in winter may actually increase the survival rate of chinook eggs. Similarly, an increase of less than one degree in winter sea surface temperatures can also increase Chinook’s chances of surviving the ocean stage of life, and snowier winters are positively correlated with salmon numbers.
However, its positive aspects are not enough to overcome its negative aspects.
“I think the feedback kind of speaks for itself,” Murdoch said.
The paper calls on fisheries managers to seriously consider the impacts of climate change when making decisions for greater cooperation across borders, and in particular to consider increasing escape targets to take environmental impacts into account.
“Salmon are faced with these warmer and more unpredictable environments every year, which of course means they may not be able to produce like they used to,” Murdoch said. “And management goals developed based on these old conditions may not be as effective moving forward.”
But one salmon expert said he wished the researchers had taken their analysis a step further.
Sebastian Jones is a fish, wildlife and habitat analyst with the Yukon Conservation Society and was not involved in the research paper. He said he was surprised that researchers had not examined how historical overfishing in both the ocean and the river had weakened the chinook population and made it more susceptible to negative environmental impacts.
“It would be really great to see a similar newspaper that casts its net a little wider, so to speak,” he said.
But he said he supported the call for higher escape targets and thought the paper would still be useful in upcoming executive meetings.
Murdoch acknowledged that the paper should not be taken in isolation and said its findings should complement other ongoing research.
“There are definitely things we didn’t address in our study that could be included in future iterations of this study or other studies,” he said.
“Our main message from this is that we really need to consider the big picture of all the potential threats that salmon may face when making these management decisions.”