Salmon of the Pacific Coast.
Five species of Salmon are found along the Pacific coast, as far south as Monterey Bay, California and as far east as Siberia. Chinook, or King Salmon is the largest, recorded at 127 lbs but normally between 18 & 24 lbs. Pink salmon do not migrate far up stream to spawn, but are found typically in coastal streams. All Pinks spend 18 months at sea, so all returning Pink salmon were borne in the same year and therefore do not interbreed with different year classes. Sockeye typically return after 2 years at sea. When they enter the fresh water, both male & females develop bright red bodies & green heads. Chum, the second largest salmon species, lives for up to 7 years, but normally after 4 to spawn. The males develop large canine teeth when they spawn, so are commonly referred to as Dog salmon. The Coho are powerfully built and can jump falls that other salmon cannot. Their fry spend more than a year living in streams before going to sea for 18 months, returning to their home stream as 3 year olds weighing 8-10 lbs.
Life cycle of Pacific Salmon.
After 1-7 years at sea, when conditions are right, an unknown signal triggers the migration home. Some would have traveled 2000 miles in their lifetime, somehow find their way across trackless miles of ocean, even in overcast weather, when neither sun nor stars can aid navigation. When they reach the coast, they pick up scent of the home rivers, their sensitive noses being able to detect dissolved substances as diluted as 1 in 3 000 000 000 000 000 000.
Once they enter the fresh water, they stop feeding, living on stored fats & muscle long enough to take them past the various hurdles, including building nests & fighting for dominance, on their way to the spawning grounds. They undergo many physical changes, depending on species, like developing bright colours, humped backs, hooked jaws & large canines while at the same time loosing their ability to fight disease & their digestive tract degenerates.
The females select a nesting site with the right combination of gravel, oxygen, depth & water flow, She excavates the nest by rolling on her side & pumping her tail, until the depth is perfect.
Males fight for dominance, before courting the female by quivering his body & crossing over her back. When she is ready to lay, he moves alongside her and they release eggs & milt. They will both soon die, but the female will guard the nest until she is too weak to continue.
Eggs lie on the gravel through the winter as the embryo develop. In spring yolk sac fry hatch, they do not leave the protection of the gravel for at least 12 weeks or until the yolk is used up. Now the fry swim to the surface, gulp air to fill their swim bladder & begin to feed. Chum & Pink salmon fry will immediately head out to sea, all the others will spend a year or more in the streams, living mainly on insects. Environmental cues cause physical changes; scales become larger, tails longer & deeper forked & their colour turns silvery. They allow the current to carry them down stream, where they linger in the estuaries, allowing their bodies to adjust to the salt water, feeding voraciously, before finally heading out to sea. Some will travel over 2000 miles, before returning to the exact same river, to complete the cycle.
Adults face many man made challenges; they become confused in slack water where dams have been built, expend precious energy in the turbulent water below dam walls trying to negotiate these obstacles, pollution and especially erosion when clear cutting of forests has taken place, disruption of courting when near humans & many more. Whilst in the steams their lives are made more difficult when water has been diverted, vegetation been removed along rivers allows access by livestock & changes to the river system resulting in both flooding and drought. Finally the smolts, as salmon are known when they first return to sea, have to deal with slack water where not only do they have to expend precious energy but they become easy prey to birds, larger fish, mammals & particularly introduced species like squawfish. They are also weakened by pollution and suffer due to loss of habitat where they would normally get food.
But man is doing his bit to try to improve the situation; in northwestern Washington, the Olympic National Park is gearing up for the biggest dam removal project in US history. Two dams on the Elwha River will be removed in 2011, allowing salmon to return to 70 miles of stream in a pristine area.
Each year, 54 hatcheries release more than 50 million salmon back into the rivers. In order to aid harvest management, each fish is Coded Wire Tagged; a tiny magnetized stainless steel wire with a diameter of 0.25mm and 1,1mm long is hypodermically injected into the snouts of the fish. Each tag is marked with 2 rows of numbers detailing specific batch information or individual codes. The equipment used to undertake this work is obviously expensive, so trailers costing up to a million dollars, serve the various breeding units. When the trailer arrives, fish from the runways are pumped to the sorting system.
Video imaging sorts fish into preselected size categories, the fish is then held gently by the machine, before insertion of the coded wire and then being returned to the raceway. If for what ever reason the fish cannot be processed within 5 seconds it is released.
In addition, the adipose fin of each fish is removed as a marker to allow fisherman to distinguish captive breed from wild salmon. Wild salmon have to be returned to the river, while the captive breed can be harvested. Modern facilities remove the fin in a similar fashion to the tagging, however many are still done manually. Fish brought to the trailer are rapidly anaesthetized, the fin cut off by a trained crew member, before being revived in fresh water and then returned to the raceways.
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