If climate change has caused the dramatic decline in Yukon River Chinook, can anything fix it?
By Jacqueline Ronson
For nearly 20 years, there has been a mystery playing out on the banks of the Yukon River and its tributaries: What happened to all the chinook salmon? Chinook (or king) salmon are prized for their large size and rich, oily flesh. Before 1997 the Yukon River runs averaged 300,000 fish, but there hasn’t been a run of 100,000 in a decade. In 2013, the return was just 37,000 fish.
Getting to the bottom of the mystery is a massive technical challenge. The Yukon River watershed covers 320,000 square miles of Alaska and Canada’s Yukon Territory, the majority of which is inaccessible by road. Chinook salmon begin their lives in spawning streams throughout this vast wilderness. After hatching and developing in fresh water for a year or two, the juveniles migrate out to the Bering Sea, where they mature into adults. At age four, five, or six, the adult chinook return home to the stream where they were born. Some travel 2,000 miles to the headwaters of the Yukon River. It is the longest freshwater salmon migration in the world.
So far, researchers have mostly been at a loss to explain the precipitous decline in the salmon population. Perhaps there’s one major cause — some environmental disruption that has affected all of the Yukon River chinook across their enormous habitat. Or maybe it is a culmination of stresses, all of which contribute to a precipitous decline. In either case, the disappearance of the chinook shows no sign of abating.
The response to the problem to date has been predictable: tighten fishing restrictions, limit harvests. It’s a sensible response. “I never met a fish that can read a fishing regulation, so fishery management must be about managing people,” says fisheries biologist Phil Mundy. He works for the National Oceanic and Atmospheric Association as the director of its Auke Bay Laboratories in Juneau.
The communities that fish for food along the river have been hit particularly hard. This past summer and the one before were the first ever when no subsistence harvest of chinook was permitted.
But there’s a limit to what you can accomplish with fishing restrictions, and in the case of the Yukon River chinook, it might not be enough. The chinook have a fundamental productivity problem, which means that, for each adult pair that makes it back to the spawning grounds, fewer than two of their brood of eggs will survive to reproduce themselves. Fishing less will put more salmon on the spawning beds, but until the productivity issue is resolved, the numbers will only go down.
For the Yukon River chinook, managers are already reaching the limit of what can be accomplished by restricting harvest. New strict rules have dramatically reduced the by-catch of chinook salmon by ocean trawlers, which used to receive most of the blame for the declining salmon runs. The in-river harvest, too, has been cut down to effectively nothing. The past two seasons, the allowable catch of Yukon River chinook has been zero. It’s a huge change from just a decade ago, when harvests of more than 100,000 chinook throughout the watershed were common. The communities that fish for food along the river have been hit particularly hard. This past summer and the one before were the first ever when no subsistence harvest of chinook was permitted.
It’s hard to overstate just how important the salmon are to the Alaska Native and Yukon First Nations communities that live in the vast Yukon River watershed. The people of Alaska and Yukon have had a relationship with the fish for thousands of years, gathering on the river banks each summer in time for the great migration, harvesting and drying the food to get through another long, cold winter. The dependence of these communities on the salmon is not a thing of the past. Most Yukon River communities are not accessible by road, and residents depend on fishing and hunting to survive.
Beyond the importance of the fish as a source of food and economic activity, chinook hold a cultural and spiritual importance to the indigenous people that eat it. When a couple dozen Yup’ik fishermen went to court for their principled violation of a chinook fishing ban in 2012, they argued that their religion compelled them to fish. Men wept openly in the courtroom as they spoke of the pain they felt in the salmon’s absence. “I have a grandchild, two years old,” said Felix Flynn, one of the defendants, according to The Atlantic’s coverage of the trial. “My grandson said to me, ‘When we gonna go check the net?’ And I couldn’t say anything.”
The fishermen lost the court case, and the subsequent appeal, but the trial judge was clearly sympathetic to their plight. “When this case goes up for appeal,” Judge Bruce Ward said, “the cold transcript will not reflect that everyone in the courtroom was standing, and that record will not reflect that there are a number of people in the courtroom with tears in their eyes.”
It’s becoming clear that climate change likely has a major role in the decline of the salmon population. It’s impossible to live in Alaska or the Yukon and be blind to dramatic ways that a warming environment has already impacted the ecosystem: melting permafrost and glaciers, warmer winters, wetter summers, changing vegetation and wildlife patterns. In Alaska and the Yukon, average temperatures have already increased by about three degrees Fahrenheit on average. Winter temperatures have soared by twice as much.
How is the changing environment impacting the salmon? The NOAA’s Phil Mundy has a theory. Scientists know that water temperature affects the timing of the salmon life cycle. If young fish are reared in warmer water, they will grow up faster in general. “Where on Earth are the areas that are warming the most rapidly, of all of the areas of global warming?” he asks. “The northern portion of the watershed of the Yukon River salmon.”
“There may be a long period when there are practically no chinook salmon in the Yukon River, depending on how rapidly global warming occurs. From a human perspective that will be a tragedy, because it will take many human generations for those fish to snap back.”
So perhaps the solution to the mystery is this: Young salmon are growing up too soon in their warmer freshwater habitats. As a result, they leave for sea too early. “The young fish [are] filing down the river, going out into the ocean at a time when their species has evolved to expect food,” says Mundy — namely, the blooms of plankton that fill the north Bering Sea every year. But unlike the freshwater habitats, the chinook’s ocean habitat has not warmed much, and the timing of the blooms hasn’t changed significantly. And so the fish that get to the ocean too soon starve and die.
Mundy doesn’t yet have enough evidence to back up his hypothesis, but he’s working on it. The Yukon River chinook have such a complicated life cycle and spend their lives over such a vast and remote geography that there are still major holes in our understanding of them. The summer of 2015 was only the second year that data was collected on the timing of juvenile fish entering the Bering Sea. Before that, it’s anyone’s guess.
If Mundy’s right, then the news is pretty bad — what it means is that all of the harvest restrictions and by-catch limits and habitat restoration efforts combined may be insufficient to maintain a healthy population of chinook in the Yukon River watershed. “There may be a long period when there are practically no chinook salmon in the Yukon River, depending on how rapidly global warming occurs,” Mundy says. “From a human perspective that will be a tragedy, because it will take many human generations for those fish to snap back.”
Ultimately, though, Mundy is hopeful that the chinook will find a way to thrive. “I’ve studied salmon for most of my adult life, and I never ceased to be amazed by how tough they are, and by how adaptable they are,” he says. He’s seen it before, with the chinook of the Columbia River basin and the sockeye of Lake Washington, which are both environments that are much more heavily disturbed by human infrastructure than the Yukon River.
When the Lake Washington Ship Canal opened in 1916, it lowered the lake level and cut off the Black River, which previously had provided access for salmon. Predictably, the sockeye population collapsed. In an effort to restore the stock, managers spent 18 years importing sockeye from the Skagit River watershed in northern Washington. “They put them in there and they put them in there, and they didn’t get any returns so they just threw up their hands and they walked away and they said ‘we’ve failed,’” Mundy says. “Well, 10 years after they threw up their hands and walked away, they had 100,000 sockeye salmon come screaming up the Ballard Locks.”
What happened, Mundy says, is that the vast majority of the Skagit sockeye were maladapted to the Lake Washington environment, and they died. But a very small few — maybe just one in 1,000— lived, and passed on their genes to descendants, who were also well adapted to the new environment. Over generations, these sockeye were able to replenish the ecosystem with a healthy population of fish.
The same thing will happen in the Yukon, Mundy says. Most of the fish will get to the ocean too early, missing the timing of the plankton blooms. But a select few will be OK. “The laggards, the ones that go slow, will still be matched up pretty well with the food in the northern Bering Sea when they go out into the ocean, and they’ll have enough to eat,” he says. “If I’m right, what that means is that only the descendants of the slow migrators are going to survive, so their timing — their phenology — will adapt; it will shift to match the new circumstances.”
Slowly, those fish that are hardwired to go slow will take over, and their population will rebound. “If the spawning habitats are left intact, then I’m very optimistic that the Yukon River will be a chinook run, and perhaps one of the world’s biggest chinook rivers, in the future.”
This isn’t a guaranteed outcome: If the ecosystem shifts faster than the ability of the fish to adapt over the long term, then it could spell disaster. But based on the climate change projections Mundy has seen, he still believes the chinook will win out in the end.
“I would put my money on the salmon,” he says.