Atlantic Salmon: Characteristics, Migrations and Collapse

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Atlantic salmon

Atlantic Salmon (Scientific name: Salmo salar) have a spindle-like body shape — rounded, broad in the middle, and tapered at each end. The shape is somewhat flattened toward the sides, which is typical of salmon species. The head is relatively small, about one-fifth of the body length. The underside paired fins are prominent, especially on juveniles. [Source: NOAA]

Also known as sea run salmon, Kelts, fiddler, grilt, landlocked salmon; puananiche, Sebago salmo and black salmon, Atlantic salmon fish have a black, gray head and shiny silver body. Spawning adults darken to a bronze color after entering freshwater and darken further after they spawn. When spawning has been completed, they are often referred to as kelts or black salmon. Their silver color returns after they re-enter the sea.

Atlantic salmon are the only salmon native to the Atlantic Ocean. They have traditionally lived in the North Atlantic Ocean, basis from the Arctic Circle to Portugal in the eastern Atlantic, from Iceland and southern Greenland, and from the Ungava region of northern Quebec south to the Conneticut River. There are three groups of wild Atlantic salmon: North American, European, and Baltic. The North American group, including the Canadian and U.S. populations, was historically found from northern Quebec southeast to Newfoundland and southwest to Long Island Sound. [Source: Vanessa Renzi, Animal Diversity Web (ADW)]

Larger adult Atlantic salmon mainly prey on fish such as Atlantic herring, alewife, rainbow smelt, capelin, mummichogs, sand lances, flatfish, and small Atlantic mackerel. Birds, marine mammals, and fish prey on Atlantic salmon..

The major difference between Atlantic and Pacific salmon is that Atlantic salmon may spawn more than once while Pacific salmon die soon after one spawn. Long ago, some people made boots out of salmon skin! The Atlantic salmon's sense of smell is 1000 times greater than that of a dog.

Websites and Resources: Animal Diversity Web (ADW); National Oceanic and Atmospheric Administration (NOAA); Fishbase ; Encyclopedia of Life ; Smithsonian Oceans Portal

Atlantic Salmon Characteristics

Atlantic salmon

Atlantic salmon weigh between 2.3 to 36 kilograms (5 to 79 pounds). Sea-living Atlantic salmon usually attain a larger size than do landlocked (those living in entirely fresh water) salmon. Sea-run salmon range from 2.3 to 9.1 kilograms and commercially caught fish average 4.5 to 5.4 kilograms. The world record rod-caught Atlantic salmon weighed 36 kilograms and was caught in the Tana River of Norway.[Source: Vanessa Renzi, Animal Diversity Web (ADW)]

According to Animal Diversity Web: The adult Atlantic salmon is a graceful fish, deepening rearward from a small pointed head to the deepest point under the dorsal fin, then tapering to a slender caudal peduncle which supports a spreading and slightly emarginate caudal fin. Atlantic salmon are distinguished from the Pacific salmon because they have fewer than 13 rays in the anal fin. Their mouth is moderately large. The shape, length of head, and depth of body vary with each stage of sexual maturity.

Color varies with age of this fish. Small "parr," older young salmon, have 8 to 11 pigmented bars, or "parr marks," along each side of their body, alternating with a single row of red spots along the lateral line. These markings are lost when the "smolt" age is reached. Salmon in the sea are silvery on the sides and belly, while the back varies with shades of brown, green, and blue. Atlantic salmon also have numerous black spots, usually "X"-shaped and scattered around the body. When spawning, both sexes take on an overall bronze-purple coloration and may acquire reddish spots on the head and body. After spawning, the "kelts" are so dark in color that these fish are also called "black salmon"

Atlantic Salmon Spawning and Development

Atlantic salmon are anadromous — they leave the ocean to return to freshwater streams and rivers to breed. After hatching, young Atlantic salmon (called parr) remain in rivers or streams for the first 1 to 2 years of life, preferring shallow, cool, fast-flowing water with shade. After this period, the salmon migrate to open ocean waters where they spend about 2 to 3 years feeding, then return to their natal streams or rivers to spawn during the fall.. [Source: NOAA]

range of the Atlantic salmon

Unlike the Pacific salmon species, Atlantic salmon do not die after spawning, and adults can repeat the breeding cycle. They live for 4 to 6 years. After spawning is completed, the fish, now called "kelts," may drop downriver to a pool and rest for a few weeks, or they may return at once to the ocean. Some may also remain in the river over winter and return to sea in the spring.

Females lay an average of 7,500 eggs in gravel nests, called redds. Eggs incubate slowly due to cold winter water temperatures. About nine to 20 percent of the eggs survive to the fry stage. Fry remain buried in the gravel for about 6 weeks and emerge in mid-May. They quickly disperse from the redds and develop camouflaging stripes along their sides, entering the parr stage.

Parr eventually undergo a physiological transformation called smoltification that prepares them for life in a marine habitat. During smoltification, fish imprint on the chemical nature of the stream or river to enable them to find their way back to where they were born. After smoltfication is complete in the spring, smolts migrate to the ocean to grow, feed, and mature.

Relatively large cool rivers with extensive gravelly bottom headwaters are essential during their early life. According to Animal Diversity Web (ADW): Tagging has shown that while some salmon wander, the great majority return to the river in which they were spawned. When at sea, salmon seem to prefer temperatures of 4̊ to 12̊ C (39̊ to 55̊F). They may withstand exposure to temperatures in their lower lethal limit (-.7̊C, 31̊F) and their upper lethal limit (27.8̊ C, 82̊F), but only for a short period of time. [Source: Vanessa Renzi, Animal Diversity Web (ADW)]

The rate of which Atlantic salmon hatchling grows varies a great deal. In the cold rivers of Scandinavia, where food is scarce, they can take as long as seven years to reach four inches in length. In England they can take as little as a year to reach the same size. Once they have reached that size they begin their journey downstream. Atlantic salmon growth rates are variable and depend on several factors including season, habitat quality, age, sex, and population density. They grow much faster in saltwater than in freshwater. After 2 years at sea, adult salmon can grow to an average length of 71 to 76 centimeters (28 to 30 inches( and weight of 3.6 to 5.5 kilograms (8 to 12 pounds). Juvenile Atlantic salmon mostly prey on invertebrates and terrestrial insects while in freshwater and on amphipods (small, shrimp-like crustaceans), krill, and fishes while at sea.

Collapse of Atlantic Salmon

In the United States, Atlantic salmon were once native to almost every river north of the Hudson River. Stocks of the fish began to decline in the mid-1800s due to a number of factors including habitat destruction, historic overfishing, industrial and agricultural development and dams. Most populations native to New England were eradicated. Now, the only native populations of Atlantic salmon in the United States are found in Maine. [Source: NOAA]

Atlantic salmon were a highly prized game and food fish. They were caught by Native Americans before the first settlers arrived, and commercial fisheries for Atlantic salmon started in Maine during the 1600s. Around the time of the American Revolution, weirs (an enclosure of stakes set in a stream as a trap for fish) became the gear of choice in U.S. Atlantic salmon commercial fisheries and were modified as more effective materials and designs became available. Recreational fishermen have reportedly been catching Atlantic salmon since 1832, when the first Atlantic salmon caught on rod-and-reel gear was captured in the Dennys River in Maine.

Before the industrial revolution, an estimated 10 million Atlantic salmon migrated annually to the rivers of North America and Russia and as far south as Portugal in Europe. The Thames, Rhone, Connecticut and Hudson rivers all welcomed large numbers of the fish. In colonial America they were so common in New England that servant begged their masters to be fed it no more than twice a week. Rivers blocked by dams and fouled by pollutants impeded the ability of salmon to migrate. Places where salmon were so plentiful that people got sick of eating salmon and used them for fertilizer now have no fish.

In “Four Fish: The Future of the Last Wild Food” Paul Greenberg estimates that somewhere in the range of a hundred million salmon larvae used to hatch in the Connecticut River each year. Now the number’s a lot easier to pin down: it’s zero. “The broad, complex genetic potential of the Connecticut River salmon,” Greenberg writes, has “vanished from the face of the earth.” Catches in Maine exceeded 90 metric tons in the late 1800s and 45 metric tons in some years during the early 1900s. [Source: Elizabeth Kolbert, The New Yorker, August 2, 2010]

The Atlantic salmon population was dealt a serious blow when their man feeding grounds were discovered off of Greenland in the 1960s and they were heavily fished. They have also suffered from acid rain, shrinking ocean habitat and the netting of young salmon by herring and mackerel trawlers. In Scotland, a moth repellant, used in making tweed, that entered the water system killed salmon by causing deformities in young fish. Salmon raised in healthy rivers are dying mysteriously at sea.

Today the population of Atlantic salmon is significantly below target population levels. Rebuilding plans are in place. The U.S. Atlantic Salmon Assessment Committee, a team of state and federal biologists, collects data on Atlantic salmon throughout New England and assesses the species’ population status. According to the 2020 stock assessment Atlantic salmon are overfished and returns remain at historically low levels. Scientists determine the population status by counting the number of adults that return to spawn, either directly at traps and weirs or indirectly using nest surveys and modeling.

Atlantic Salmon Fishing Ban and Recovery

Commercial and recreational fishing for Atlantic salmon in the United States is prohibited. In addition, some populations are protected under the Endangered Species Act. Only farm-raised Atlantic salmon are found in U.S. seafood markets. Recreational fisheries are closed in the United States, with the exception of some landlocked fisheries for Atlantic salmon in New Hampshire, where fish retired from hatchery broodstock are released for angling. [Source: NOAA]

Atlantic salmon

Atlantic salmon are managed under the Fishery Management Plan for Atlantic Salmon by NOAA Fisheries, the U.S. Fish and Wildlife Service, the New England Fishery Management Council, and the State of Maine. Possession of wild Atlantic salmon and any directed or incidental Atlantic salmon catch in federal waters is prohibited. All Atlantic salmon caught incidentally in other fisheries must be released in a manner that ensures maximum probability of survival. This protects Atlantic salmon in U.S. marine waters and complements management in state-managed riverine and coastal waters.

In 2000, NOAA Fisheries and the U.S. Fish and Wildlife Service listed the Gulf of Maine distinct population segment of Atlantic salmon as endangered under the Endangered Species Act. The two agencies are jointly responsible for the recovery of this endangered population of Atlantic salmon. In December 2005, the agencies, in coordination with the State of Maine, finalized the Recovery Plan for the Gulf of Maine distinct population segment. This plan identifies recovery actions needed to halt the decline of the species and lays out a process to minimize threats.

Because Atlantic salmon migrate all along the North American coast, the United States joined with other North Atlantic nations in 1984 to form the North Atlantic Salmon Conservation Organization (NASCO) to cooperatively manage Atlantic salmon stocks through conservation, restoration, and enhancement programs.

Substantial efforts are ongoing to restore wild Atlantic salmon and their habitat. These include improving fish passage by removing or modifying dams so salmon can reach freshwater spawning and rearing areas critical to their survival, understanding and improving historically low salmon survival in the ocean, and supplementing wild populations with hatchery-raised Atlantic salmon.

Collapse of the Atlantic salmon

Image Sources: Wikimedia Commons, NOAA

Text Sources: Animal Diversity Web (ADW); National Oceanic and Atmospheric Administration (NOAA); Wikipedia, National Geographic, Live Science, BBC, Smithsonian, New York Times, Washington Post, Los Angeles Times, The New Yorker, Reuters, Associated Press, Lonely Planet Guides and various books and other publications.

Last Updated April 2023

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