Atlantic salmon. Credit: NOAA Fisheries.
Atlantic salmon. Credit: NOAA Fisheries.
About the Species
Atlantic salmon, also known as the “King of Fish,” are anadromous, which means they can live in both fresh and saltwater. Atlantic salmon have a relatively complex life history that begins with spawning and juvenile rearing in rivers. They then migrate to saltwater to feed, grow, and mature before returning to freshwater to spawn.
Atlantic salmon are vulnerable to many stressors and threats, including blocked access to spawning grounds, habitat degradation caused by dams and culverts, and poor marine survival. They are considered an indicator species or a “canary in the coal mine.” This means that the health of the species is directly affected by its ecosystem health. When a river ecosystem is clean and well-connected, its salmon population is typically healthy and robust. When a river ecosystem is not clean or well-connected, its salmon population will usually decline.
Atlantic salmon in the United States were once native to almost every coastal river northeast of the Hudson River in New York. But commercial fishing in Atlantic salmon fisheries reduced their population size until the fisheries closed in 1948. Commercial and recreational fishing for wild sea run Atlantic salmon is still prohibited in the United States. All Atlantic salmon in the public market is cultured and commercially grown. Currently, the last wild populations of U.S. Atlantic salmon are found in at least eight rivers in Maine. These populations comprise the Gulf of Maine distinct population segment, which is listed as endangered under the Endangered Species Act. Some populations in southern Canada and Europe are also declining significantly, creating concern about the status of this species globally. In addition, the Gulf of Maine DPS is one of nine Species in the Spotlight. This means that NOAA Fisheries has made it a priority to focus recovery efforts on research to better understand the major threats and stabilize the Gulf of Maine DPS by improving access to quality habitat and thus, preventing its extinction.
Our dedicated scientists and partners use a variety of innovative techniques to conserve Atlantic salmon and to protect and rebuild depleted endangered populations. NOAA Fisheries also works with partners to protect critical habitat for the Gulf of Maine DPS and makes every effort to engage the public in conservation efforts.
Population Status
Worldwide, Atlantic salmon populations in single rivers range from thousands to nearly a quarter million. However, some populations are small, numbering in the low hundreds or even single individuals.
The endangered Gulf of Maine DPS has declined significantly since the late 19th century. Historically, dams, overfishing, and pollution led to large declines in salmon abundance. Because of this, the commercial Atlantic salmon fishery closed in 1948. Improvements in water quality and stocking from hatcheries helped rebuild populations to nearly 5,000 adults by 1985. But more recently, scientists have discovered marine survival and populations have significantly decreased, resulting in annual returns to the United States of generally less than 1,000 adults. The rapid decline and dire status of the ESA-listed Gulf of Maine DPS makes it a priority for NOAA Fisheries and partners to prevent its extinction and promote its recovery.
Protected Status
Appearance
While in freshwater, young Atlantic salmon—known as “parr”—have brown to bronze-colored bodies with dark vertical bars and red and black spots. These markings camouflage and protect them from predators. Once young salmon are ready to migrate to the ocean, their appearance changes; their vertical barring disappears and they become silvery with nearly black backs and white bellies. When adults return to freshwater to spawn, they are very bright silver. After entering the river, they will again darken to a bronze color before spawning in the fall. After spawning, adults—now called “kelts”—can darken further and are often referred to as “black salmon.” Once adults return to the ocean, they revert to their counter-shaded coloration dominated by silver.
Typically, an Atlantic salmon returning to U.S. waters will be 4 years old, having spent 2 years in freshwater and 2 years at sea. These fish are called “two sea winter fish,” or 2SW, and are usually 28 to 30 inches long and 8 to 12 pounds. The size of adults returning to freshwater from the ocean depends on how long they lived at sea. Young salmon returning to freshwater after 1 year at sea (known as “grilse” or 1SW) are smaller than 2SW adults. Adult salmon can migrate several times to spawn—a reproductive strategy known as iteroparity—though repeat spawners are becoming increasingly rare.
Behavior and Diet
Atlantic salmon are migratory. They travel long distances from the mouths of rivers to the Atlantic Ocean before returning to their natal rivers. For example, U.S. salmon leave Maine rivers in the spring and reach the seas off Newfoundland and Labrador, Canada, by mid-summer. They spend their first winter at sea south of Greenland and their second growing season at sea off the coast of West Greenland and sometimes East Greenland. Maturing fish travel back to their native rivers in Maine to spawn after 1 to 3 years.
The diet of Atlantic salmon depends on their age. Young salmon eat insects, invertebrates, and plankton. The preferred diet of adult salmon is capelin. Capelin (similar in appearance to rainbow smelt) are elongated silvery baitfish that reach 8 to 10 inches in length.
Where They Live
There are three groups of Atlantic salmon: North American, European, and Baltic. These groups are found in the waters of North America, Iceland, Greenland, Europe, and Russia. Atlantic salmon spawn in the coastal rivers of northeastern North America, Iceland, Europe, and northwestern Russia. After spawning, they migrate through various portions of the North Atlantic Ocean. European and North American populations of Atlantic salmon intermix while living in the ocean, where they share summer feeding grounds off Greenland. The North American group historically ranged from northern Quebec to Newfoundland and to Long Island Sound. This group includes Canadian populations and U.S. populations. In Canada, healthy populations still exist throughout the historical range but many populations are severely depleted.
World map providing approximate representation of the Atlantic salmon's range.
Lifespan & Reproduction
Atlantic salmon have a complex life history and go through several stages that affect their behavior, appearance, and habitat needs. They are anadromous, which means that they are born in freshwater, migrate to the ocean as adults, and then return upriver to spawn.
When spawning in the fall, the female salmon uses its tail to dig nests in the gravel where the eggs are deposited. These nests are called redds. Over winter, the eggs develop into very small salmon called alevin. In the spring, the alevin swim out of the redd and are then called fry. Fry grow into parr, which are only 2 inches long and are camouflaged to protect them from predators. For 2 to 3 years, the parr grow in freshwater before transforming into smolts in the early spring. The silvery smolts’ gills and organs change, allowing them to swim to the ocean where they spend 1 to 2 years maturing into adults.
The adult Atlantic salmon, or kelt, returns to the river where it was born to lay eggs. After spawning in freshwater, the kelt can swim back to the ocean and possibly return to spawn again.
Females returning to spawn after two winters at sea lay an average of 7,500 eggs. Out of these eggs, only about 15 to 35 percent will survive to the fry stage.
Threats
Atlantic salmon populations are exposed to a variety of threats. The most significant threats to their survival include impediments—such as dams and culverts—that block their access to quality habitat, ongoing subsistence fisheries off the shores of Greenland, and changing conditions at sea. Salmon also face many other threats that affect their survival, such as poor water quality, degraded freshwater habitats from land use practices, disease, predation from introduced and invasive species, and interbreeding with escaped fish raised on farms for commercial aquaculture.
Learn more about threats facing the endangered Gulf of Maine population of Atlantic salmon
Marine Survival
Marine survival is the primary driver of population productivity for Atlantic salmon. During years with high marine survival, populations are expected to be robust and to increase, whereas during years of low marine survival, populations are expected to decline. Unfortunately, U.S. Atlantic salmon are currently in a period of persistent, poor marine survival. During the early 1990s, oceanographic changes in the Northwest Atlantic had major impacts on the dynamics of many marine species, including Atlantic salmon. These changes led to significant decreases in marine survival for Atlantic salmon across their North Atlantic range—from Labrador south to the United States. Although the exact reasons for the decrease are unknown, scientists hypothesize that the oceanographic changes altered dynamics up the food chain from primary production to prey fish and even Atlantic salmon. These changes were severe enough to similarly impact the productivity of other marine species (e.g., Atlantic cod, Bluefin tuna, seabirds, marine mammals).
Habitat Impediments
Dams block Atlantic salmon migration paths between rivers and the ocean and can prevent salmon from reaching the habitats needed for spawning and juvenile rearing. Turbines used to generate electricity can kill or injure many salmon as they migrate through dams on their journeys to the ocean. Injuries caused by dams may result in delayed mortality or increase salmon vulnerability to other threats, such as predation by other fish or birds. Dams can also increase the amount of time salmon need to migrate, disrupting their life cycle in the process. These impediments impact river ecosystems by changing river flows, reducing water quality, and changing water temperature. Dams also destroy habitats important to other fish species that salmon have evolved to depend on (e.g., migrating alewives can buffer Atlantic salmon against predation from birds and other fish) and provide habitats for fish species that compete with or prey on Atlantic salmon.
Habitat Degradation
Land use practices can degrade freshwater habitats necessary for Atlantic salmon survival. For example, forestry, agriculture, and development projects damage or destroy riparian areas that protect streams from erosion. These areas also provide habitat structure, essential nutrients, and forage that salmon depend on in the form of falling trees, leaf litter, and bugs that fall from the forest canopy.
Pollution
Pollution causes poor water quality that may impact Atlantic salmon. Pollution can reduce the levels of oxygen in the water, making areas unsuitable for salmon survival, and it can deliver chemicals that are toxic to fish or that react with other chemicals to increase toxicity to fish. Pollution also adversely affects Atlantic salmon’s homing abilities and alters the water chemistry, which can impair the salmon’s ability to regulate its own body chemistry. Water quality can affect salmon differently depending on their life stage. For example, juvenile salmon may experience reduced growth, while adults may produce fewer eggs.
Fish Harvest
Atlantic salmon are threatened by gillnet fisheries, bycatch in recreational fisheries, and poaching. International commercial fishing has been highly restricted since 2002, but this issue has recently become a growing concern. In areas with recreational fishing, fishermen might accidentally or unknowingly catch Atlantic salmon. Even if salmon are released after being caught, they are particularly susceptible to post-release mortality from injury or stress.
Disease
Atlantic salmon can be affected by many pathogens (bacterial, viral, and fungal) found in the wild, which can lead to different diseases. A severe disease outbreak can potentially affect many individuals or an entire year class or life stage within an Atlantic salmon population. Atlantic salmon are also vulnerable to parasites, and there is strong evidence that commercial aquaculture facilities are a primary source of parasites for naturally occurring populations of Atlantic salmon. Best management practices and good fish husbandry have minimized the risks from disease and parasites. In addition, all commercial and federal hatcheries follow strict disease prevention practices. These practices help protect natural and hatchery environments from pathogens. If a disease does break out in a hatchery, managers also take steps to control the spread of the pathogen between hatcheries and river systems.
Aquaculture
Aquaculture, or fish farming, refers to the breeding, rearing, and harvesting of marine plants and animals for public use. Aquaculture of Atlantic salmon provides the world with a healthy food source that would not be available through other means such as a wild fishery. However, commercial aquaculture of Atlantic salmon has well-documented genetic and ecological threats on wild salmon populations. These threats include interbreeding between wild and farmed individuals as well as pathogen and parasite transfers to the wild populations that live near commercial operations. Most fish raised for aquaculture purposes are closely related to their wild counterparts; however, through artificial selection during spawning, the genetic composition of farmed fish is different and less fit than wild populations. If they escape and breed with wild fish, the offspring produced will contain genes from the farmed origin parent and would be less fit for survival in the wild. While producers go to great lengths to make sure farmed fish never enter the environment and interact with wild fish, accidents have happened in the past and may be anticipated in the future. Recent improvements in manufactured gear (net pens and mooring systems) for rearing fish in open ocean environments has decreased the likelihood of escapes. Additional marking of these fish has helped to better understand the causes and helps to minimize these risks. But even with these changes, aquaculture fish still put wild Atlantic salmon at risk.
Scientific Classification
| Animalia |
Chordata |
Osteichthyes |
Salmoniformes |
Salmonidae |
Salmo |
salar |
