by Yukon River chinook salmon are likely to be significantly affected by environmental conditions and that’s something fisheries managers need to pay attention to, according to a new scientific paper.
In the paper, published in the latest issue of the Canadian Journal of Fisheries and Aquatic Sciences, researchers drew on decades of data on “environmental and ecosystem variables” such as water temperature, precipitation and the date of ice breakup on the. Yukon River at Dawson City. They then looked at the impact these variables might have on chinook at different stages of life, from eggs to mature fish returning to their spawning grounds.
The impacts were not “trivial,” lead author Alyssa Murdoch told CBC News in an interview.
“We were finding it on the scale, you know, losses of about thousands of fish,” she said.
In particular, the researchers found that wetter conditions in the Yukon River watershed could have a negative impact on young sockeye – less than three centimeters of additional rainfall could result in an average loss of more than 13,000 salmon.
That’s because more rain means higher water flow, which can displace the young fish and disrupt their feeding.
Murdoch also cited the finding that a 1.2 C increase in water temperature in the Yukon during chinook spawning migration could reduce run size by an average of 12,000 fish.
“Twelve thousand salmon is really huge for very low returns when you count all the fish,” she said.
In recent years, the sizes of Chinook runs on the Yukon River have declined significantly, with 2022 and 2023 being the worst and worst runs on record, respectively. According to preliminary numbers for the year 2023, only 58,529 mussels entered the mouth of the river in Alaska, of which 14,752 are estimated to have entered Canada — only about a third of the number needed to fill the lower part of the achieve the goal of phase restriction.
Other environmental factors that researchers found likely to have a negative impact on chinook included increased precipitation during spawning and egg incubation, warmer and longer springs and summers, and an increase in pink salmon numbers in the ocean.
A later ice breakup date in the Yukon at Dawson City could also have a negative impact, with researchers theorizing that the ice has been in place longer, delaying floes getting to coastal and ocean areas .
The temperature and precipitation findings are especially relevant, the paper says, since the Yukon’s watersheds are expected to become warmer and wetter as the climate changes.
Warmer water can be positive in some cases, according to researchers
Murdoch said, however, that researchers also found that chinook are “very complex,” and that environmental changes can have a positive effect in some cases.
Warmer water during spawning and during the winter, for example, could improve the survival of the marrow eggs. Similarly, an increase in sea surface temperature of less than a degree in winter may improve the survival of chinook in the ocean life stage, and snowier winters were positively correlated with salmon numbers.
However, the positives are not enough to outweigh the negatives.
“I think the returns kind of speak for themselves,” said Murdoch.
The paper calls on fisheries managers to seriously consider the impacts of climate change when making decisions, for more cross-border collaboration, and in particular, for managers to consider increasing phase-out targets to include environmental effects included.
“The salmon are facing these warmer and more unpredictable environments every year and of course that means they may not be able to produce like they used to,” said Murdoch. “And the management goals that were developed based on these older conditions may not be as effective going forward.”
One salmon expert, however, said he wished researchers would take 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 researchers hadn’t looked at how historical overfishing, both in the ocean and the river, weakened the chinook population and made it more susceptible to negative environmental impacts.
“It would be great to see a paper like it that casts its net, so to speak, but a little wider,” he said.
However, he said he supported the call for higher step-down targets, and thought the paper would still be useful in future management meetings.
Murdoch agreed that the paper should not be viewed in isolation, and said its findings are meant to complement other ongoing research.
“There are certainly things involved that we are not involved in in our study and they could be included in future iterations of this or other work,” she said.
“Our main message from this is that we need to really look at all the threats that salmon may be facing when making these management decisions.”
