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Atlantic Salmon > EcologySalmo salar - meaning 'the leaper' - was named and described scientifically in 1758 by Carolus Linnaeus, a Swedish taxonomist and botanist, but it was not until well into the first part of the 19th century that it was proven that the adult Atlantic salmon was the same species as the striped parr found in the rivers.
Physical CharacteristicsThe body of 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.Salmon have attributes that are river-specific, which is reinforced by the fact that with only a few exceptions, they live and mate within the river system of their birth.
Life CycleThe 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.
Threats:
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.
The genetic diversity of the population is being wiped out as more and more rivers lose their wild salmon. In the Baltic, for example, of the 120 rivers that supported salmon a century ago, only 37 have naturally spawning stocks today.
Ocean fisheries in parts of the Atlantic continue to catch salmon from a mixture of river systems in an indiscriminate and unsustainable manner. This practice is undermining already endangered salmon runs in many places.
Dams and other impediments to fish passage prevent salmon from reaching historic spawning habitat in many important salmon rivers.
In some areas, irresponsible salmon fish farm (or "aquaculture") operations pose additional problems since they can act as a source of disease and parasites. Plus, escaped farmed fish threaten the genetic and ecological integrity of wild salmon populations.
