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 A salmon goes through many changes as it grows and becomes an adult. These changes are part of its life cycle. Each stage is different from the others. Early eash spring, thousands of tiny Atlantic salmon alevin emerge from pea-sized orange eggs deposited in riverbeds the previous autumn. The alevin, about 2cm long, feeds on the yolk of the egg from which it hatched while it is still in the gravel. The yolk is contained in a seac attached to the belly of the fish. When the yolk sac is nearly gone, the tiny salmon wriggles its way up through the gravel out into the stream. Now it will feed on microscopic life in the water. It is finally on its own. Until the young fish is five to 8 cm long, it is called a fry. These fry soon aquire the markings on either flank that identify them as parr. A parr has a dark back with nine to eleven bars, called parr marks, along its sides. a single red dot occurs between each pair of parr marks. These markings help camouflage the parr while it lives amoung the rocks and weeds of the river. Parr remain in the river for 2-6 years (determined by water temperatures and the availability of aquatic insects, crustations ans small fish), until it is time to go to sea. From egg to parr stage, young salmon are hunted by larger fish, birds and mammals; they are also affected by changes of survival over this period are less than one in a thousand. At a length of 12-24 cm, parr undergo a springtime transformation into a smolt. Parr marks are replaced by a silvery coat for camoflauge. It would be dangerous for the fish t oenter the sea with brightly-colored stripes and spots! Their internal systems adapt for saltwater life and the fish leave their freshwater nursery, the odors of the smolt's native river are imprinted in its memory, to be recalled when it returns t ospawn. Salmon from both sides of the Atlantic rendezvous in the waters off southwestern Greenland; others travel to lesser-known oceanic or coastal feeding areas. They grow rapidly on a small diet of small crustation and fish while eluding capture by larger fish and sea going-mamals. After one or more years at sea, following a hereditary route and timetable, Atlantic salmon return to their home rivers in an extrodinary journey that may span more than 4,000 Km of open ocean. Entering the river between April nad November, they navigate up stream, leaping obstructions up to 3 m high, to spawn in shallow tributaries in late fall. Fish that return after one year at sea are termed grilse; these ususally weigh 1-2 Kg and are more often male. Those returning after two or more years at sea are called salmon and weigh 4-20 Kg. Once in fresh water, Atlantic salmon stop feeding until they re-enter the oceean a few weeks later or as long as 12 months later. During this period, the male salmon's head will develope a Kype, or hooked lower jaw, and certain internal systems of both sexes will degenerate in favor of egg or sperm (Milt) production. In late fall, the female uses strong thrusts of her tail to dig a 10-30 cm deep nest or redd, in the riverbed. Her eggs and the milt are released into the redd, the gravel is replaced with additional tail thrusts and the process is repeated until all the eggs are deposited. A female salmon may lay 1,500 - 1,600 eggs for each Kg of her own weight. Repeat spawners may produce u pto 50% mor eggs than maiden fish. While the eggs await spring hatch, the surviving adults (now termed kelt or black salmon) return to ocean feeding grounds immediately or after over-wintering in the river. As they feed, the physical and phycological degeneration that has occured in fresh water is reserved. One in ten kelt may survive the hazards of another ocean migration and spawn a second time, and a few will complete 3-6 cycles. This extrodinary behavior distinguaishes the Atlantic from the Pacific salmon, all of which die after their first and only spawning. Some Atlantic salmon populations have becomes 'landlocked', inhabiting lake systems in areas bordering the North Atlantic. These landlocked or 'ouananiche' salmon follow a cycle similar to sea run salmon, mirgrating deep lake feeding areas and spawning grounds along shorelines or in tributaries. They average 20-60 cm in length and less than 4 Kg in weight. Every Scale Tells A Story  The most widespread method of aging salmon parr and adults involves collecting scales collected from the large number forming the protective outer coating of each fish. When clean and undamaged, scales show progrssive growth rings similar to the rings of trees. As the salmon grows, new groth rings are laid down in the scales. The scales, with their growth rings, can be magnified to accurately reveal the life history of individual salmon. |
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Main The Atlantic Salmon The Salmon Life Cycle The Fisheries Managing The Resource Aquaculture Brook Trout Hatchery Process Image Gallery | ||
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