Salmo salar

Salmo salar
source
Name	Salmo salar
Status	LC
Status system	IUCN3.1
Genus	Salmo
Species	salar
Authority	(Linnaeus, 1758)

Salmo salar. Commonly known as the Atlantic salmon, it is an anadromous fish of the family Salmonidae native to the temperate and Arctic regions of the North Atlantic Ocean. It is renowned for its complex life cycle, which involves long oceanic migrations and a dramatic return to freshwater rivers to spawn. The species holds significant ecological, cultural, and economic importance across its range, from North America to Europe.

Description and morphology

The species exhibits considerable morphological variation between its freshwater and marine phases. Juvenile fish, known as parr, display distinctive dark vertical bars along their flanks for camouflage in riverine environments. Upon transitioning to the smolt stage in preparation for ocean migration, they take on a silvery sheen with a blue-green back. Adult salmon in the ocean are streamlined and silvery, often with black spots scattered above the lateral line. Upon re-entering freshwater to spawn, males undergo a dramatic transformation, developing a hooked jaw, or kype, and vibrant red and green coloration, while females become a dull bronze. They possess an adipose fin, a characteristic feature of the family Salmonidae, and have a fusiform body shape built for sustained swimming.

Life cycle and reproduction

The life history is a classic example of anadromy, beginning when adults spawn in the cool, gravel-bottomed reaches of freshwater rivers like the River Tay in Scotland or the Miramichi River in New Brunswick. After hatching, the alevins remain in the gravel before emerging as fry and then parr, which may spend one to eight years in freshwater. These parr undergo smoltification, a physiological transformation allowing them to osmoregulate in saltwater, before migrating to the rich feeding grounds of the North Atlantic, such as the seas off Greenland and the Faroe Islands. After one to four years at sea, adults navigate back to their natal river using geomagnetic and olfactory cues, a phenomenon studied extensively at institutions like the University of Washington. Spawning is followed by senescence, with many individuals dying, though some, known as kelts, may survive to return to sea.

Distribution and habitat

Historically, its range extended from the Connecticut River northward along the coast of North America to Ungava Bay, and across the Atlantic from Portugal north to Russia, including the Baltic Sea. Key populations are associated with major river systems including the River Spey, the Seine, and the Kola Peninsula. It requires cold, well-oxygenated freshwater for spawning and juvenile rearing, and productive marine environments for the adult growth phase. The species is now extirpated from many southern parts of its historical range, such as much of the United States, due to anthropogenic pressures. Introduced populations exist in the Southern Hemisphere, notably in Patagonia.

Conservation status and threats

The International Union for Conservation of Nature lists the species as Least Concern globally, but many regional populations, particularly in southern Europe and North America, are endangered. Major threats include habitat degradation from activities like forestry and agriculture, which increase siltation and water temperature. The construction of dams, such as those on the Penobscot River, has blocked access to historic spawning grounds. Other significant pressures are overfishing in both commercial and recreational fisheries, aquaculture impacts like sea lice transmission and genetic introgression from escaped farmed fish, and the broader effects of climate change on ocean temperatures and prey availability like capelin. Conservation efforts involve habitat restoration, fish passage improvements, and international agreements under bodies like the North Atlantic Salmon Conservation Organization.

Relationship to humans

The Atlantic salmon has been a vital resource for millennia, evidenced by archaeological finds in sites like the Mesoamerican cultures and sustenance for peoples such as the Míkmaq. It is the basis of major commercial and sport fisheries in regions like Norway, Iceland, and Canada, celebrated in events like the River Test. The rise of intensive aquaculture, pioneered in countries like Chile and Scotland, has made farmed salmon a globally traded commodity, though not without controversy regarding environmental impacts. The fish holds a prominent place in art and literature, from the poetry of Ted Hughes to the paintings of Winslow Homer, and is central to culinary traditions, featured in dishes from Nova Scotia to Moscow.

Category:Ray-finned fish Category:Fish of the Atlantic Ocean Category:Commercial fish