Yukon River: Scaling Fish
Salmon spawners get over a dam
The Yukon River is one of the most important salmon-breeding rivers in the
world. Each year, the river and its tributaries witness the return of huge
Chinook salmon to spawn in tributary creeks. Returning salmon have been a vital
food source to aboriginal peoples for thousands of years.
Some experts believe the salmon use a powerful sense of smell to trace their route back
to gravel beds where they were hatched six or seven years earlier. However they find their
way, the salmon migration begins far out at sea where salmon mature. Yukon salmon that
have been hatched and tagged near Whitehorse, were later caught as far away as Japan.
Until 1957, the Yukon was free-flowing from its headwaters in British Columbia all the
way to the Bering Sea on the north coast of Alaska. Salmon swam freely through the Whitehorse
Rapids to spawn in the tributaries and creeks upstream of Whitehorse.
The river was dammed at Whitehorse in 1957 to provide electrical power for the small city.
The salmon's natural migration route past Whitehorse was suddenly blocked by the power
To provide a partial remedy, an artificial channel - the Whitehorse Fishway - was built
beside the dam. The Fishway is 366 metres in length, the longest wooden fish ladder in
The Fishway is a sloping trough fitted with a series of partitions. Water courses down
the trough from the reservoir behind the dam, flowing over and through the partitions.
The partitions slow the flow and provide climbing fish with resting places. The fish can
jump over the partitions but most swim through the underwater doorways joining each compartment.
Halfway up the Fishway, the salmon enter a viewing chamber where they are counted and
measured by Fishway staff looking through glass windows. The fish are then removed from
the viewing tank with nets and placed in the upper section of the Fishway to complete their
climb over the dam.
By the time they reach the Fishway, the salmon are exhausted and fringed with fungus growing
on their injured skins. They have spent three months swimming the 3,000 kilometres of the
Yukon River, without eating.
The digestive systems of all Pacific Ocean salmon degenerate at the start of the migration.
By the time they reach the upper reaches of the river, they have just enough energy and
determination remaining to built nests and spawn. Soon after despositing and fertilizing
their eggs in the gravel nests they build by swishing their tails, both male and female
Some of the fish are removed from the Fishway and taken to a nearby hatchery. There, the
eggs are squeezed from the females and sperm, called milt, is squeezed from the males.
The eggs are fertilized with the milt and hatched artificially in tanks. The following
spring the baby fish, or fry, are released by teams of students into creeks upstream from
Whitehorse. This artificial hatching of salmon eggs is needed to make up for the loss of
naturally-hatched fry who are killed by the turbines of the power plant as they try to
make their way downstream towards the sea.
Very few of the salmon hatched or released upstream of the dam ever make it back home
after spending their adult lives in the Pacific Ocean. Most will be eaten by other fish
or trapped at sea by commercial fishing boats. Some years, only 150 salmon return to the
The biggest return since the dam was built was in 1996 when nearly 3,000 salmon were counted.
Fishway staff believe the reason for the large return was the fact that the fish had managed
to escape the fishing boats by returning two weeks sooner than expected.
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