Sound Salmon Background Information for teachers
The Salmon Life Cycle
Only about 20% of the eggs in a stream will hatch. Many of the eggs succumb to predators, oxygen deprivation or physical damage. A newly hatched salmon or alevin emerges with a yolk sac attached to its abdomen. Alevins live in the gravel and survive by absorbing the protein, sugars and vitamins from their yolk sac. After a few weeks the yolk is gone and the small fish called parr move into deeper water and begin to find food on their own. Vertical stripes on its sides help to hide the parr from predators.
Salmon parr remain in freshwater feeding and growing for many months or even years before migrating downstream to saltwater. When they are about as bi9 as a human finger they are called fingerlings. They hide and feed among the plants and wood debris in the river.
Feeding in the estuary where fresh and saltwater intermingle doubles or triples the size of the smolt. After a few weeks of growing and adjusting to saltwater, young salmon swim into the ocean. The ocean provides salmon with abundant food including shrimp and other crustaceans which help to color their flesh pink. Adult salmon also eat anchovies, herring and other fish. In the ocean, salmon are a bright silver color. They spend one to five years at sea depending on their species.
Salmon migration is an astounding feat still not fully understood. Juvenile salmon imprint or memorize the unique organic odors of their home streams. As returning adults they can detect and recognize these odors and follow them upstream sometimes to the exact areas where they hatched. Before making this upstream migration, however, the salmon must find its way to within smelling distance of the river. Salmon from throughout the Pacific Northwest intermingle in the oceans where they travel in broad circular patterns. It is thought that they use currents, salinity and temperature patterns, the sun, Stars, and the earth’s magnetic field to aid them in traveling from sea to river mouth.
Not all salmon return to their home stream at the same time of year. There are different runs of salmon that return from the sea at various times and seasons. Each run is genetically unique and specifically adapted to their stream. Some salmon migrate over 1000 miles up river to spawn. On their way, each species develops unique coloration and patterns. Male salmon spawners also develop long, hooked snouts and sharp, canine-like teeth. Changes in the female are similar but less pronounced. They gather at the river's mouth to await heavy rains before moving upstream. During upstream migration salmon do not feed.
When salmon reach their spawning grounds males and females pair off. Females look for rippling waters and clean streambed gravel that can be swept aside with broad tail strokes. The scooped-out gravel forms a depression about the shape of the female's body but twice as long. Males compete to spawn with the female. Sometimes smaller males called jacks are also present. Jack salmon are small because they migrate after only a year in the ocean but can spawn nevertheless. The female deposits some of her eggs in the redd and the male fertilizes them with a milky cloud of sperm called milt. Eggs are laid in batches deposited within the redd. Spawners guard the nest to protect it from intruders. Most Pacific salmon die within one to two weeks after spawning.
The Nutrient Cycle
Hazards for Salmon
Habitat destruction - Throughout their lives salmon depend on cold, clean, well-oxygenated water. Their freshwater habitat must include plants to shade streams, deep pools of water to rest in and clean gravel for spawning. Poor logging practices, grazing, mining, road-building and urban development often destroy streamside vegetation, erode the land and fill streams with silt that smothers gravel beds.
Harvest - during the heyday of Northwest commercial fishing salmon stocks seemed limitless. We know now that overfishing, combined with habitat destruction, was one of the first causes of salmon decline. Harvest today is highly regulated but can still be a problem when endangered stocks are caught unintentionally with non-endangered ones. Technology has made it possible to harvest many or even all the fish. Fishing must be carefully managed so that salmon continue to be a harvestable resource.
Hydropower - Hydroelectric dams block migration to and from the ocean. Many dams lack fish ladders. The downstream migration of young salmon is hampered by the huge reservoirs of water that form behind dams where juvenile fish are exposed to unhealthy conditions, high temperatures and predators. Fish that pass through the turbine blades of dams are often injured or killed.
Hatcheries - Hatcheries developed as a way to compensate for the loss of salmon habitat to dams, agriculture and urbanization. They effectively protect salmon eggs and rear young fish to the time of freshwater release. At that point, salmon must cope with whatever conditions exist for the downstream migration, in the ocean, and later, as they return to spawning grounds. Hatchery-reared fish may transmit diseases to wild fish and they compete with wild fish for food and habitat. Interbreeding with hatchery fish dilutes the genetic diversity and vigor of wild stocks. Modified hatchery practices can help to enhance salmon stocks but will never be a substitute for habitat protection and restoration. Despite large numbers of hatcheries in Washington State, salmon runs in the Northwest have steadily declined. Fewer fishing days are available to fishermen than ever before. Less fish are caught and the size of those fish tends to be smaller than salmon of the past.
Two Native American Perspectives from First Fish - First People Salmon Tales of the North Pacific Rim