Yukon River Salmon
The three primary salmon species of concern addressed under the Yukon River Salmon Agreement are Canadian-origin:
- Chinook (Oncorhynchus tshawytscha, commonly referred to as ‘king’ salmon)
- Chum (O. keta, commonly referred to as ‘dog’ salmon), and
- Coho (O. kisutch, commonly referred to as ‘silver’ salmon).
Two other species of Pacific salmon are also found within the Alaskan portion of the Yukon River drainage, including sockeye salmon (O. nerka, commonly referred to as ‘reds’) and pink salmon (O. gorbuscha, commonly referred to as ‘humpies’).
All species of Pacific salmon are anadromous as they spawn in freshwater and spend at least a part of their lives in the ocean. To spawn, each female salmon uses her tail to create a depression in the gravel, with a dominant male salmon beside her. The female salmon releases her eggs in this depression or nest, which is commonly referred to as a redd. As the female releases her eggs, the dominant male salmon simultaneously releases a cloud of milt, or sperm, to fertilize the eggs. Subordinate males may join the spawning pair at this time and also attempt to fertilize the eggs with their milt. The fertilized eggs develop during the winter, and hatch in late winter or early spring, depending on the time of spawning and water temperature.
Salmon hatch as alevins, with an attached yolk sac for food, and live in the gravel for several weeks until they gradually absorb all the food in the yolk sac. They emerge from the gravel as fry. Some species of salmon fry remain in the freshwater system for longer periods than others, and some do not have a prolonged freshwater residence at all. Most Yukon River drainage Chinook salmon spend one to two years rearing in fresh water before their out-migration to the ocean. On the other hand, emergent Yukon River chum fry migrate immediately to the mouth of the river spending little time in the freshwater system. Young salmon migrating to the sea are called smolt. As the process of smoltification occurs (during a limited time span), coordinated morphological, physiological and behavioral changes occur in preparation for the salmon’s transition from fresh water to salt water. Time spent at sea varies between Pacific salmon species from 18 months to 6 years. Chinook salmon from the Yukon River spend, on average, four years at sea (ranging between 1 to 6 years).
Chum salmon spend an average of three years at sea (ranging between 2 to 5 years). No matter how long the duration, all time at sea is spent growing. Sub-adult salmon grow rapidly in the ocean and often double their weight during a single season. Small, sexually-mature adult salmon that return to spawning grounds after spending only a few months to one winter in the ocean are commonly referred to as jacks, and are usually males. Within the Yukon River drainage, jacks are most noticeable in the Chinook salmon populations, although they do occur in coho and sockeye salmon populations as well.
As sexually-mature adults, salmon travel hundreds, even thousands, of miles/kilometers from ocean feeding areas to spawn in the same freshwater system in which they hatched. Some headwater salmon stocks migrate over 1,840-miles (2960 km) to reach their spawning grounds in the Yukon Territory and northern British Columbia, thereby making some of the longest salmon migrations in the world.
Little is known about the navigation mechanisms salmon use when at sea, although some evidence suggests they may be able to use the Earth’s magnetic field as an indicator. Once near their natal streams, river or lakes, adult salmon use olfactory cues, or smell, to return to the spawning grounds where they originated.
Adult salmon going the furthest to spawn tend to possess the highest oil content of any salmon when they begin their upstream journey. Salmon do not feed during their spawning migration, so their condition deteriorates gradually during their migration as they use stored body reserves for energy. As female salmon travel to spawning grounds their eggs gradually mature, becoming larger in preparation for delivery or spawning. Therefore, it is local belief that smaller eggs and smaller bunches of eggs in female salmon are an indication the salmon has a longer way to travel before spawning.