Salmon

Common Name:
Salmon
Scientific Name:
Salmo salar and Oncorhynchus
Diet:
Omnivore
Group Name:
School
Average Life Span:
Three years to seven years
Size:
1.5 feet to just under four feet

What is a salmon?

Salmons include seven species of Pacific salmon and one species of Atlantic salmon. They’re found in tributaries of the Pacific and Atlantic Oceans, and most species are anadromous: They are born in streams and rivers, migrate out to the open sea, and then return to freshwater again to reproduce. 

Salmons have sleek, streamlined bodies that typically change color throughout their lifetimes. While in freshwater, Atlantic salmon are brown and spotted. When they migrate to the ocean, they turn silvery. Atlantic salmon are the largest salmon species, typically growing to just under four feet in length. 

Pacific salmon undergo significant transformations when returning to freshwater from the ocean: Some species go from silver to a deep maroon; others turn a deep black. Male sockeye salmon develop humps on their backs. The seven species of Pacific salmon typically range in length from a foot and a half to two and a half feet.

Wild salmon is fished extensively for food, both recreationally and commercially. The Atlantic salmon was nearly fished to extinction—the commercial market is now almost exclusively farm-raised fish. (Here are some tips to make sure you’re buying sustainable salmon.)

Many species of salmon are considered keystone species—vital to the health of their ecosystem.

Habitat

Atlantic salmon were once abundant throughout the North Atlantic coast off the U.S. and Canada, but overfishing and habitat destruction following European settlement dramatically reduced their numbers. In the U.S. today, Atlantic salmon are found only in a handful of rivers in Maine. In addition to the small North American population, groups of Atlantic salmon are also found in coastal rivers of northeastern Europe, including Iceland and northwestern Russia. 

Pacific salmon species are found throughout the western U.S. and Canadian Pacific Northwest, as well as in Japan.

Migration

Salmon are known for their grueling migrations. All species are born in freshwater streams and migrate to the ocean as juveniles. Sockeye salmon stay for up to three years in their natal habitat—longer than any other salmon. 

Adult salmon typically spend one to five years in the ocean, where they feed mainly on zooplankton, before returning to freshwater streams to spawn. This perilous, exhausting journey, sometimes hundreds of miles long against the current, is called a “salmon run.” Salmon use smell to navigate back to their original spawning grounds.

Pacific salmon die within a few weeks of spawning, as do most male Atlantic salmon. Ten to 40 percent of female Atlantic salmon, however, survive and return to the sea

Importance in ecosystem

Some species of salmon are considered keystone species—vital to sustaining their ecosystems. The sockeye salmon, for example, is a keystone species in Alaska’s Bristol Bay, which is part of Katmai National Park. As the salmon spawn and begin to die, their carcasses decompose and fertilize the soil of the river banks and boreal forests of the park. The plants then pass along the nutrients to the many animals that live and thrive in the region.

The Atlantic salmon, vulnerable to many stressors and threats including habitat degradation, is considered an indicator species—its health reflects the health of its ecosystem. 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 tributaries are blocked by dams or land development, for instance—its salmon population will usually decline.

Salmon as food

Salmon is the most popular fish in the U.S.—Americans collectively consume nearly 450,000 tons each year. Many Pacific salmon species in the U.S. are wild-caught, with fisheries managed in partnership between local and federal authorities.

Commercial fishing of wild Atlantic salmon, however, has been banned in the U.S. since the late 1940s. Today, all Atlantic salmon consumed in the U.S. is farmed, often imported from as far away as Chile, Scotland, and Norway.

It might seem that eating farmed salmon would be good for the environment—farming reduces pressures on wild populations and protects other wildlife, including threatened and endangered species, from being caught as bycatch in fishing nets. But environmental groups have compared salmon aquaculture facilities to floating pig farms for their high rates of pollution, disease outbreaks, antibiotic use, and infestations of sea lice, marine parasites that feed on the flesh and blood of their fish hosts, causing injury and stress.

Threats

Crucial to the survival of wild salmon is the preservation of suitable habitat for them to spawn and their offspring to grow. Historically, artificial dams, overfishing, and pollution have led to large declines in Atlantic salmon. In the U.S., Atlantic salmon are listed as endangered and are federally protected. The International Union for Conservation of Nature (IUCN) has listed the species as vulnerable to extinction. 

Many Pacific salmon, too, have faced rapid declines. The overall population of chinook salmon, for example, has declined by 60 percent since 1984. Local populations of four Pacific salmon species—chinook, coho, chum, and sockeye—are protected under the Endangered Species Act. 

Beaver dams have proved helpful to salmon recovery in some cases. In the Elwha River, a key tributary for chinook salmon in northwest Washington, chinook populations have almost doubled since major, human-made dams were removed in 2014. A key element of that has been the arrival of beavers in the river. Their dams have helped increase the volume of water, slow its flow, and trap sediment, allowing for more habitat for a variety of species, including salmon. The beaver dam-created tidal pools in the river support three times as many juvenile chinook and other salmon species as areas without beavers.

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