Salmon Facts

Adults generally run 2 to 3.5 feet and 8 to 35 pounds, though much larger fish were common before overfishing truncated their age structure. At sea the body is sleek and silvery with a steely blue-green back and small X-shaped spots — countershaded camouflage for open water. But re-entering freshwater to spawn, adults remodel dramatically: they stop feeding, their guts shrink as energy shifts to the gonads, their color turns to dark bronze and mottled red, and males grow a hooked lower jaw (a kype) and enlarged teeth for fighting rivals. The key internal trick is osmoregulation — specialized chloride cells in the gills reverse their ion-pumping to excrete salt at sea and retain it in freshwater, letting the salmon survive a salinity swing lethal to most fish. It belongs to the family Salmonidae and, unlike Pacific salmon that die after one spawning, is iteroparous — able to survive, return to the sea, and spawn again.

Salmo salar ranges across the North Atlantic basin — in the west from northern Quebec and Newfoundland down through the northeastern U.S. (historically as far as the Connecticut River), and in the east from Arctic Norway and Russia's White Sea down through the UK and Ireland, once to Portugal and Spain. Its needs are phase-specific: juveniles require cold, clean, highly oxygenated streams with gravel beds and riffles and pools, while maturing adults roam the open North Atlantic, often to rich feeding grounds off Greenland and the Faroe Islands.

Diet shifts sharply with life stage. Newly hatched alevins live on their yolk sacs; as fry and parr in the river, they hold feeding territories in the current and dart out for aquatic insect nymphs, terrestrial insects, and tiny fish. Once they migrate to sea as smolts, they become pelagic carnivores, feeding voraciously on energy-dense forage fish like capelin, sand lance, and herring, plus krill, amphipods, and shrimp — and the carotenoid pigments in those crustaceans are what tint the salmon's flesh pink-red.

At sea salmon are largely solitary or in loose feeding shoals, but their defining trait is the homing migration: using the Earth's magnetic field, currents, and temperature to cross thousands of miles of ocean back to their natal river mouth, then switching to a fine-tuned sense of smell to identify their birth stream by its unique chemical signature. On the spawning grounds competition is fierce — females seek gravel with good subsurface flow while males ram and bite rivals with their kypes. Small "precocious parr" that never went to sea use a sneaker strategy, hiding near a spawning pair and darting in to fertilize some eggs.

The cycle begins in late autumn when a female digs a gravel depression (a redd) with her tail and lays hundreds to thousands of eggs, fertilized by a dominant male and buried in gravel. They incubate through winter and hatch in spring into alevins, then emerge as feeding fry, develop camouflage "parr marks," and live in the river 1 to 3 years. Reaching a size threshold, they undergo smoltification — parr marks fade, bodies turn silver, and osmoregulation shifts for saltwater — and migrate downstream on spring floods. After 1 to 4 years growing at sea they mature and head home; many die of exhaustion after spawning, but survivors (kelts) can return to the sea and spawn again.

Globally Salmo salar is listed as Least Concern, buoyed by huge aquaculture and some stable stocks — but wild populations have collapsed regionally, with local extirpations. Dams and impassable culverts sever migrating salmon from spawning grounds, while agricultural runoff, pollution, and deforestation smother gravel beds with silt and push water temperatures past tolerance. Historical overfishing depleted breeding stocks, and open-net-pen aquaculture now adds serious biological threats: concentrated pathogens like sea lice and infectious salmon anemia, and genetic damage when escaped farmed fish breed with wild salmon and depress their fitness.

• IUCN Red List: Atlantic Salmon
• World Wildlife Fund: Salmon
• NOAA Fisheries: Atlantic Salmon
• North Atlantic Salmon Conservation Organization (NASCO)