Chinook salmon spend about a year and half in freshwater before making the journey to the ocean.

While chinook salmon tend to get the most attention during their epic spawning runs in the summer, Yukon’s waters are teeming with the fish year-round — including during the winter.

In fact, that’s when Yukoners are surrounded by the highest number of chinook, according to a Whitehorse fish biologist, although they’re hidden under the ice and much smaller than the bright-red giants most people are used to seeing. 

Yukon River chinook salmon will spend about a year and half in freshwater before making the journey to the ocean, which is much longer than their counterparts further down south. While some southern chinook juveniles will leave for saltwater their first summer, Yukon River chinook actually spend two winters in the watershed — the first, immediately after hatching, and the second as juveniles that will begin migrating in the spring. 

Newly-hatched chinook, which emerge from that year’s eggs in the early winter, are called alevin and spend the colder months biding their time in the gravel. (It’s unclear how many chinook salmon hatch every year, but a female salmon can lay between 5,000 to 10,000 eggs).

They eventually emerge as hungry little fry who spend the rest of their time in freshwater snapping up as many small invertebrates as possible, finding spots where the water doesn’t freeze and staying out of the way of predatory fish like pike. 

By the time the ice breaks up in the spring, Chinook who have made it through their second winter are only about the length of a finger but prepared to make the more than 3,000-kilometre journey to the Bering Sea. While there is a degree of the “mad rush” seen with the adult spawning migration, there are a few differences for young salmon heading for saltwater — they’re swimming with the current instead of against it, and are also eating along the way. 

The migration typically peaks in mid-June. About 95 per cent of the chinook salmon are now in the “smolt” life stage, having hit the ocean by mid-July, where they’ll spend several years before returning home. 

Not all juvenile chinook salmon make the journey, though — there are rare cases where male fish will actually spend their entire lives in freshwater, from hatching to spawning. 

Barker said those chinook are unofficially known as “sneakers,” because they only grow to about the size of a hand and can’t attract egg-laying females on their own when spawning season finally rolls around. 

 “They have to rely on the big ocean-going males to find females and convince them to spawn, and then they’ll dart in underneath them, hoping not to be detected and release milt to fertilize those eggs,” he explained. 

The unusual situation is an evolutionary gamble of sorts. On one hand, the longer a fish lives, the bigger it can get. Being a larger fish means being able to carry more eggs or milt, and having the ability to dig a better nest in the gravel. On the other hand, the longer anything is alive, the higher the chance it’ll die before it can reproduce. 

While Fisheries and Oceans Canada has done monitoring and survey work in the past, juvenile chinook salmon aren’t tracked nearly as closely as their adult counterparts; some parts of their world remain a mystery.