The Salmon Life Cycle

A female salmon may lay 3000-5000 bright pink eggs in the nest called a redd that she digs in the gravelly streambed. After the male fertilizes the eggs they absorb water and become sticky. The female moves upstream to lay more eggs. Gravel from the next nest is pushed downstream and covers the first nest. The eggs grow and develop for a few months before hatching.

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
Although Pacific salmon do not survive to care for their young, their deaths are an important factor in the survival of young salmon and the health of the ecosystem. The decaying bodies of salmon that have spawned release nutrients that support plant and insect life that in turn nourish salmon parr or fry Some 22 species of mammals or birds directly feed on living or dead salmon, including: raccoons, otters, humans, bears, flying squirrels, jays, moles and shrews. Altogether, 98 species have a direct or indirect link to salmon through the food web. Salmon are a valuable source of nutrients. Adult salmonids gain more than 95% of their final weight while they are in the ocean. When they return to spawn and die, they transfer those nutrients including nitrogen, phosphorous and carbon to freshwater systems. The nutrients from salmon are a key link in the overall productivity of our aquatic and terrestrial ecosystems.

from Orca Network (http://www.orcanetwork.org/habitat/salmoncycle.html)

 

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