Saltwater Salmon (SALMO SALAR)
The body of the Saltwater Salmon (SALMO SALAR)also known as the Atlantic salmon is elongated and hydrodynamic - laterally compressed, with a slender tail base. Its mouth is at the front of its head and it has sharp teeth. Atlantic salmon have a total of 15 to 20 gill rakers, and four sets of gills. Its fins include dorsal, adipose (posterior dorsal), caudal with a distinct fork, anal fins, pelvic fins, pectoral fins. The Atlantic salmon has 58 to 61 vertebrae.
The wild Atlantic salmon undergoes many changes during its life. Pea-sized orange eggs are deposited in riverbeds in autumn. Early the following spring thousands of tiny newly hatched salmon, or alevin, emerge. These alevin are about three-quarters of an inch long and feed off of an attached yolk sac, hiding from predators in the gravel of the streambed. When the yolk sac is nearly gone the young fish wriggle up into the water, and are called fry until they are about 2 to 3 inches long.
Later, at the parr stage, these salmon acquire vertical markings on their flank. Parr have dark backs, with 9 to 11 bars, called parr marks, along their sides, which act as camouflage. Parr remain in the river for two to six years, depending on temperatures and food supply.
At a length of 4 to 9 1/2 inches, parr undergo a springtime transformation into smolt. Parr marks are replaced by a silvery coat for better camouflage at sea; internal systems adapt for saltwater life; and the fish leave their streams, travelling to ocean feeding grounds. Salmon from both sides of the Atlantic rendezvous in the waters off southwestern Greenland. Others travel to lesser-known oceanic or coastal feeding areas, where they grow rapidly on a diet of small crustaceans and fish and must elude predators including larger fish and marine mammals.
After one or more years at sea, following a hereditary route and timetable, Atlantic salmon return to their home rivers in an extraordinary journey that may span more than 2,500 miles of open ocean. If they return after one winter at sea, they are called grilse.
Entering the river between April and November, they navigate upstream, leaping obstructions up to 10 feet high to spawn in shallow tributaries in late fall.
Some Atlantic salmon populations never go to sea, inhabiting lake and river systems in areas bordering the North Atlantic. These fish follow a cycle similar to sea-run salmon, except that they migrate between deep-lake feeding areas and spawning grounds along shorelines or in tributaries. They average 8-24 inches in length as adults, and weigh less than 9 pounds.
The Atlantic salmon's sensitivity to environmental change and its dependence upon both fresh and saltwater habitats have made it sensitive to environmental pressures and high-seas overfishing. Numbers have dropped greatly in the past 50 years, and between 1994 and 1999 the number of adult fish available to return to North American rivers is estimated to have dropped from approximately 200,000 to 80,000. The Atlantic salmon is in peril on both sides of the Atlantic: Populations are at their lowest point in recorded history, and catches have declined precipitously.
Information supplied by http://www.worldwildlife.org
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