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man holding large salmonAtlantic salmon
Click to enlargediagram showing salmon life historySalmon life history

Atlantic salmon have several freshwater and marine phases during their life. In freshwater, their lives begin as eggs deposited and fertilized in “nests” called redds. Newly hatched salmon are called alevin, yet once the yolk sack has been absorbed they are termed fry. The fry stage only lasts a few weeks until noticeable vertical bars referred to as parr markings appear on their sides where they are then referred to as parr. Parr will spend one to three years in freshwater before they begin their physiological transition to smolts whereby they become adapted to live in salt water. Smolts rapidly migrate from their freshwater homes to the sea in the early spring when river flows are high and the water temperatures of the rivers are close to the water temperatures of the estuary and the bays. Upon making the transition to seawater in the nearshore waters of the Gulf of Maine, the post-smolt phase begins and lasts through the winter. At this point Atlantic salmon are termed one-sea-winter adults. Some of these adults return to spawn after one year at sea and are termed grilse. Others remain at sea for an additional year or two before returning to spawn and are termed multi-sea-winter adults. The kelt phase begins after a salmon has spawned and is returning to sea.

The Atlantic salmon (Salmo salar) is actually one species within the genus Salmo. Pacific salmon are represented by seven different species and belong to the genus Oncorhynchus.

Atlantic salmon have high post spawning mortality but are capable of surviving and spawning again while most Pacific salmon die shortly after spawning - the exception being Steelhead (Oncorhynchus mykiss).

Atlantic salmon used to be found in Long Island Sound and Central New England, but those populations have been extirpated (i.e., they ceased to exist in these rivers). Currently US Atlantic salmon are only found in a handful of rivers in Maine. The broad range of anadromous Atlantic salmon extends from the rivers of the Gulf of Maine (USA) and Portugal in the south to Ungava Bay (Canada), Norway and Russia in the north. The marine range includes almost the entire North Atlantic Ocean from 40° North latitude northward to the Arctic regions of Canada, Greenland, Svalbard, and Russia.

a landlocked salmonLandlocked salmon

A landlocked Atlantic salmon is a freshwater form of the sea-run Atlantic salmon. They are genetically considered a subspecies of the sea-run Atlantic salmon, but reside in lakes, never making the marine migration. They generally do not grow as large as sea-run fish, averaging between 12 and 20 inches long.

An anadromous fish is born in freshwater, migrates to the ocean, and returns to freshwater to spawn.

Atlantic salmon in the US, for example, hatch from eggs laid by females in freshwater. After emerging from their gravel nests (or redds) in cool streams, juveniles spend the next 1-3 years living among tributaries of main-stem Gulf of Maine rivers. When the time is right, they migrate to the oceans for 1-3 years before returning to freshwater to spawn as adults in their natal rivers, effectively completing their life cycle. Time spent in freshwater (years) before the smolt migration increases for more northerly populations.

Atlantic salmon smolts migrate to sea every year in the spring. The “smolt run” in the Gulf of Maine begins in the middle of April and is over by the beginning of June. Due to regional climate impacts, the smolt run is starting earlier than in the past. The run begins later at northern latitudes.

a salmon smoltSalmon smolt

Atlantic salmon smolt, the juvenile salmon that are ready to go to sea, are usually 2-3 years old when they begin their migration in US waters, but the smolt age often increases at higher latitudes.

Atlantic salmon go to sea to grow. The energy content and abundance of food in the ocean is much higher than in freshwater, so fish are able to grow very big, very quickly. This is important because larger fish are less susceptible to predation and the females contain more eggs. A lot of eggs are needed to produce enough juveniles that will grow to maturity and return to spawn and sustain the population.

North American Atlantic salmon migrate from their natal rivers in the spring and move into the Labrador Sea for their first summer, autumn, and winter. The following spring they move to the coastal waters of Labrador and the Canadian Arctic, West Greenland, and sometimes to the waters of East Greenland. After a second winter at sea, adults from many populations are large and mature enough to spawn, and they migrate back to freshwater areas to reproduce.

During the freshwater phase, juvenile fry and parr forage primarily on small invertebrates (e.g., mayflies, stoneflies, caddisflies, blackflies, and riffle beetles, etc.) and occasionally small amphibians and fish.

During the marine phase, immature (post-smolt) and adult salmon forage on a diverse suite of prey including fish (i.e., capelin, Atlantic herring, sand lance, barracudina and lanternfish) crustaceans (i.e., amphipods and euphausiids or ‘krill’), cephalopods (i.e., squid and octopus), and sometime polychaete worms. Right before adults enter the estuaries to begin the spawning migration, they cease feeding altogether.

a salmon smolt taken from a striped sea bass's stomachSmolt (bottom) eaten by striped bass (top)

In freshwater, juveniles are eaten by a variety of fish (smallmouth bass, striped bass, Northern pike, slimy sculpin, etc.), birds (kingfisher, double-crested cormorant, mergansers, osprey, blue heron, snowy egret, etc.), and mammals (otter, mink, etc.).

During the marine phase, Atlantic salmon are consumed by large predatory fish (Atlantic halibut, Atlantic bluefin tuna, swordfish, striped bass, etc.) sharks (Greenland shark, mako and porbeagle sharks, etc.), seabirds (Northern gannett), seals (harp, grey, harbor, etc.), and toothed whales (killer whales, dolphin, porpoise, etc.). Atlantic salmon are also caught for consumption by humans in targeted aboriginal or traditional First Nations fisheries.

The largest Atlantic salmon was 105 pounds and 60 inches. However, depending on how long they are at sea, adults returning to the Gulf of Maine rivers typically weigh approximately 7-12 lbs and are 28-32 inches long after 2 years at sea.

The maximum recorded age was 13 years old, but most Atlantic salmon that survive to reproduce, live 5 to 8 years (1-7 years in fresh water, 1-6 years in the marine environment).

Almost always. While some straying has been documented, most spawning salmon return to the river in which they were born and sometimes they even home to the very stream of their birth.

Generally from 2,500 to 7,000 depending on the size of the female (larger females have more eggs), or about 600-800 eggs per pound of body weight.

The Endangered Species Act (ESA) is a law passed in 1973 that provides for the protection and conservation of species that are at very high risk of going extinct. Atlantic salmon populations in the Gulf of Maine are listed as endangered under the ESA, meaning that they are in danger of extinction throughout all or a significant portion of their range. Before construction of dams in the early 1830’s, Atlantic salmon abundance exceeded 100,000 annual returns to US rivers; now adult returns are usually less than 1000.

There are many reasons why US Atlantic salmon population abundances are so low, but three primary causes have been suggested:

Habitat Degradation. Centuries of industrialization on New England rivers (e.g., paper and textile mills, deforestation of riparian areas and log drives) has resulted in the degradation of a lot of the fishes’ spawning and rearing habitat, effectively reducing the productive capacity of our rivers.

Passage Barriers. Barriers to passage, such as dams and hydroelectric power plants, and poorly designed culverts at road crossings can delay or prevent passage of juvenile salmon swimming downstream and adults swimming upstream, preventing or impeding them from accessing the habitats they need to survive.

Marine Survival. Recently, low marine survival has hampered the rebuilding of many Atlantic salmon populations in the Northwest Atlantic. Potential drivers that influence marine phase survival include harvest, starvation (via thermal habitat and food food-web changes), predation, and disease.

the Presidential salmon of 19511951 Presidential salmon (click to enlarge)

Salmon are raised in hatcheries to supplement natural production in rivers. US Atlantic salmon are endangered and are currently unable to produce enough juveniles under natural conditions in the rivers to support their populations. Therefore, juveniles are raised in hatcheries to various stages (i.e., fry, fingerling, parr, and smolt) to enhance survival at early life stages. Then they are stocked in the rivers at various locations with the goal that they migrate to sea then return to spawn after a few years. Stocking helps maintain Endangered populations so they don’t go extinct, giving scientists and managers more time to figure out how to restore thriving populations to Gulf of Maine rivers again.

From 2010-2015, releases of hatchery-raised Atlantic salmon smolt to supplement natural production in the streams of the Gulf of Maine resulted in adult spawning returns of approximately 0.08-0.71%. This low return rate is the result of numerous factors including high mortality in the river from downstream passage barriers (i.e., hydroelectric dams) and low marine survival due to numerous factors (e.g., disease, starvation, predation, removal/fisheries).

a fish ladderFish ladder

Fish passage is essential for adult salmon to be able to travel upriver to spawn and for salmon smolts to be able to travel down river to reach the sea. A fish ladder, or fishway, is often constructed to provide for upstream passage of fish around a dam or a natural barrier that might prevent or impede progress to spawning grounds. Downstream passage of migrating smolts and some post-spawned adults past barriers is sometimes provided by constructing a bypass structure or by allowing sufficient amounts of water to spill over a dam.

Before the decline of Atlantic salmon, anglers competed annually to land the largest spring salmon. The Presidential Salmon Tradition was born out of a Penobscot River competition when, in 1912, Karl Anderson sent his winning 22-pound salmon to President Taft. The tradition was suspended due to low salmon abundance in 1992. President George H. W. Bush was the last President to receive a Presidential salmon.

Thanks to Ruth Haas-Castro of the Atlantic Salmon Ecosystems Research Team for updating this page.

Contact and credits

Contact: NEFSC Webmaster

Taken in part from “Being a bouillabaisse of fascinating facts about fish: the most-asked questions,” NOAA Magazine, April and July of 1973.

Unless otherwise noted all color artwork is © Ray Troll 2002, © Terry Pyles, colorization 2002. These images may not be utilized in whole or in part by any entity other than NMFS without the express permission of NMFS' Office of Constituent Services and the copyright artist, Ray Troll.