As the salmon parr begin migrating toward the sea, they will begin the smoltification process. The smoltification process refers to the changes that take place in salmon as they prepare to enter the sea. These changes include the development of the silver color of adults and the tolerance for salt water.
Hydroelectric Dam
Photo courtesy of the Corps of Engineers, Portland District |
On the way to the sea, salmon parr may face many challenges such as predators, hydroelectric dams, and pollution from farms, factories, and cities.
If the salmon parr encounter hydroelectric dams, they must be careful not to be sucked into and crushed in the powerful turbines. These dams and turbines generate electricity for people. The slow-moving lakes behind the dams have little oxygen, delay the migration of salmon, and attract predators in search of easy prey. Some hydroelectric dams have installed screens, channels, and other devices to create systems which help guide young salmon away from dangerous turbines and safely to the river below the dam. These systems are called juvenile fish bypass systems.
Slow-Moving Lake
Photo courtesy of the Corps of Engineers, Portland District |
As the salmon parr pass farms, factories and cities, they may encounter pollution in the water. Sprays and fertilizers that farmers and home owners use sometimes contain toxic substances which wash into rivers, pollute water, and poison fish. The water that runs rapidly off buildings, pavement, and other impermeable surfaces in cities also wash oil, anti-freeze, and other harmful substances into the rivers. Salmon parr may also be sucked into pipes which pump the cool river water into factories to cool machinery. Other pipes pump water out of the rivers for irrigation purposes.
By the time the salmon reach the estuaries, they have silver sides, bright bluish green backs, and are called smolt. Here they will undergo osmoregulation. Osmoregulation includes the adaptation of the gills and the kidneys to salt water. After osmoregulation, the salmon head out into the sea.
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