Chinook salmon in the Yukon River can be an elusive species to study, particularly in winter. Juvenile chinook salmon generally spend one winter in the Yukon before migrating to the ocean, but not much is known about their whereabouts during this time.

The young fish overwinter in large rivers like the Yukon, as well as in smaller spawning streams. But fishery managers also wanted to know whether juvenile salmon overwinter in the myriad of small streams that are not used for spawning.

This is not a theoretical question since fishery officials have a mandate to protect salmon habitat. If juvenile salmon use a stream in winter, it means that care must be taken to protect that stream year-round, not just during the summer.

A research scientist with the Department of Fisheries and Oceans has found that juvenile salmon do indeed use small streams that are not spawning waterways. Mike Bradford has been investigating juvenile salmon on Croucher Creek near Whitehorse and Hays Creek near Teslin.

An earlier study on Croucher Creek in 1993 had indicated that juvenile salmon were present in the small stream during the winter. The road to the Whitehorse sewage lagoon crosses the creek and Sue Moodie, sponsored by the Yukon Conservation Society, had initiated the study after plans were announced to upgrade the road.

In May and June Moodie found juvenile salmon in the creek. These year-old salmon cleared out of the stream during June, but then younger juveniles moved in again a few weeks later. The assumption was that juvenile salmon were overwintering in the creek, but there was only one way to find out for sure.

Moodie is now helping Bradford with his study, and in the summer and fall of 1998 they trapped and tagged about 2,000 juvenile salmon on Croucher Creek. They were all wild salmon, as they did not have the clipped fins that identify hatchery-raised fish.

In December, the researchers returned to pools that seemed likely spots for overwintering. After cutting holes through the ice, they lowered baited traps into the pools, catching about 90 juvenile salmon. About 80 percent of these fish were ones that they had tagged earlier, indicating that the winter population in the creek is fairly stable.

Bradford hopes to resample the creek in May, to see how many juvenile salmon head out for the sea. But his study has already proved one important point: small creeks -- even non-spawning ones -- can provide important winter habitat for salmon.

Bradford says he can only speculate on why so many juvenile salmon use streams like Croucher Creek. Possibly it is because in mid-summer, when salmon do most of their growing, small creeks are warmer and clearer than larger waterways and provide a better environment for growth. The smaller streams could also provide a refuge from predators such as inconnu and pike, kingfishers and mergansers.

What the fish do under the ice all winter is still a mystery. In the summer and fall, Bradford spent time snorkeling in the creeks, observing the salmon at different times of the day. Bradford says he would have been willing to brave the cold water in December to observe the fish, but there just was not enough room under the ice in the shallow stream for him to move around.

Winter is obviously a stressful time for fish. The water is colder and has less dissolved oxygen in it, and there is less to eat. It is assumed that in winter fish conserve their energy by hiding among the cobbles and woody debris on stream bottoms for most of the day, emerging at dusk to feed on whatever insects they can find.

Chinook salmon in other parts of North America do not have the challenge of surviving a northern winter. For example, on the Sacramento River in sunny California, chinook grow quickly and begin migrating to the ocean within several weeks of hatching.

Chinook in the Yukon River are at the northern end of their range. The ones hatching in the upper reaches of the river must migrate further than any other chinook in the world. Spending an extra year or two in the river as juveniles gives them more time to get ready for the 3,000-kilometer journey.

Many mysteries remain about chinook salmon, but this study solves at least one puzzle. It also provides an important piece of information for habitat managers, according to Al von Finster, the restoration biologist with the Department of Fisheries and Oceans in Whitehorse.

"For years we have been telling people that juveniles overwinter in small streams, but people have not always believed us," he says. "This study confirms this position, and makes it easier for us to protect these important habitats."

For more information on chinook salmon, contact the Department of Fisheries and Oceans in Whitehorse at 393-6722.