What Do Salmon Eat

Understanding the Distinction Between Atlantic and Pacific Salmon

The Atlantic salmon, a member of the Salmo genus, is one species within this group. On the other hand, there are seven different species of Pacific salmon, belonging to the Oncorhynchus genus. While Atlantic salmon can survive and spawn multiple times, they generally have a shorter lifespan after spawning. In contrast, most Pacific salmon die shortly after spawning, with the exception of steelhead.

The Habitat of Atlantic Salmon

Previously, Atlantic salmon could be found from Long Island Sound to New England rivers. However, these populations no longer exist in these areas. Currently, U.S. Atlantic salmon can only be found in a few rivers in Maine.

The Reason Salmon Journey to the Sea

Atlantic salmon go to sea mainly to facilitate their growth. The ocean provides a higher energy content and abundant food, enabling fish to grow rapidly. This is significant because larger fish are less vulnerable to predators, and the females produce more eggs. A substantial number of eggs are required to ensure the survival and growth of juveniles, allowing them to reach maturity and return to spawn, thus sustaining the population.

Migration of Atlantic Salmon to the Ocean

Every spring, young Atlantic salmon, known as “smolts,” migrate to the sea. The smolt run in the Gulf of Maine commences in mid-April and concludes by early June. Due to climate changes, the smolt run is starting earlier than before in some regions, while it begins later in northern latitudes.

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Age of Atlantic Salmon During Migration to the Ocean

In U.S. waters, Atlantic salmon smolts are typically 2-3 years old when they commence their migration. However, migrating smolts at higher latitudes tend to be older.

Atlantic Salmon’s Journey in the Ocean

North American Atlantic salmon migrate from their birth rivers to the Labrador Sea during their first summer, autumn, and winter. The following spring, they move to the coastal waters of Labrador, the Canadian Arctic, and sometimes East Greenland. After spending a second winter at sea, adult salmon from different populations grow large and mature enough to return to freshwater areas to reproduce.

Understanding Landlocked Salmon

Landlocked Atlantic salmon are a freshwater variation of sea-run Atlantic salmon. Genetically, they are considered a subspecies. These salmon reside in lakes and never undergo the marine migration. Compared to sea-run fish, they tend to be smaller, with an average length ranging from 12 to 20 inches.

Dietary Preferences of Atlantic Salmon

In freshwater, young salmon primarily consume small insects such as mayflies, stoneflies, caddisflies, blackflies, and riffle beetles. Occasionally, they also eat small amphibians and fish. Once they transition to the ocean, both young and adult salmon have a diverse diet, including:

  • Fish: Capelin, Atlantic herring, sand lance, barracudina, and lanternfish.
  • Crustaceans: Amphipods and euphausiids, commonly known as “krill.”
  • Cephalopods: Squid and octopus.
  • Polychaete worms.

Just before adults migrate to estuaries for the spawning migration, they stop eating altogether.

Predators of Atlantic Salmon

In freshwater, juvenile salmon fall prey to various fish species (like smallmouth bass, striped bass, Northern pike, slimy sculpin), birds (including kingfishers, double-crested cormorants, mergansers, and ospreys), and mammals (such as otters and minks). In the ocean, Atlantic salmon face threats from:

  • Large predatory fish: Atlantic halibut, Atlantic bluefin tuna, swordfish, and striped bass.
  • Sharks: Greenland shark, mako sharks, porbeagle sharks, and others.
  • Seabirds: Northern gannets.
  • Seals: Harp seals, grey seals, harbor seals, etc.
  • Toothed whales: Killer whales, dolphins, and porpoises.
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Additionally, humans also catch Atlantic salmon for consumption, particularly in targeted aboriginal or traditional First Nations fisheries.

The Remarkable Size of Salmon

The largest recorded Atlantic salmon weighed 105 pounds and measured 60 inches in length. However, when returning to the Gulf of Maine rivers after spending two years at sea, adults typically weigh around 7-12 lbs and measure 28-32 inches long.

The Lifespan of Atlantic Salmon

The oldest known Atlantic salmon lived to be 13 years old, although most individuals that survive to reproduce have a lifespan of 5 to 8 years. Within this timeframe, they spend 1-7 years in freshwater and 1-6 years in the marine environment.

The Homing Instinct of Atlantic Salmon

Almost always, spawning salmon return to the river where they were born. In some cases, they even navigate back to the exact stream of their birth.

Egg Production of Atlantic Salmon

Female Atlantic salmon typically produce between 2,500 and 7,000 eggs, depending on their size. On average, there are approximately 600-800 eggs per pound of body weight.

The Role of the Endangered Species Act (ESA) in Salmon Conservation

The Endangered Species Act (ESA), enacted in 1973, safeguards species that face a high risk of extinction. Gulf of Maine Atlantic salmon populations are classified as endangered under this act, indicating that they are in danger of extinction throughout their range. Prior to the construction of dams in the early 1830s, over 100,000 Atlantic salmon returned to U.S. rivers annually. Currently, the adult return is usually less than 1,000.

Exploring the Decline of Atlantic Salmon in New England Rivers

The low abundance of U.S. Atlantic salmon populations can be attributed to various causes. The three primary factors are as follows:

  1. Habitat degradation: Centuries of industrialization along New England rivers, including activities such as paper and textile mills, deforestation of riparian areas, and log drives, have degraded the spawning and rearing habitats. Consequently, this has reduced the overall productivity of the rivers.

  2. Barriers to migration: Dams, hydroelectric power plants, and poorly designed culverts at road crossings hinder or prevent juvenile salmon from swimming downstream and adults from swimming upstream. As a result, salmon struggle to reach the habitats crucial for their survival.

  3. Marine survival: In recent times, fewer Atlantic salmon have been able to survive their journey to the Northwest Atlantic. Potential factors contributing to this decline include harvest, starvation due to changes in thermal habitat and the food web, predation, and disease.

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The Purpose of Salmon Hatcheries

Hatcheries raise salmon to supplement natural production in rivers. Atlantic salmon populations are endangered, and they are currently unable to produce enough juveniles under natural conditions to sustain their populations. Therefore, young salmon are raised in hatcheries to various stages of development (fry, fingerling, parr, and smolt) to enhance their survival during early life stages. These individuals are then stocked in rivers, allowing them to migrate to the sea and return to spawn after a few years. Stocking helps maintain and prevent the extinction of endangered populations. This approach provides scientists and managers with additional time to devise strategies for restoring thriving Atlantic salmon populations in Gulf of Maine rivers.

Adult Returns from Hatchery Releases

From 2010 to 2015, the release of hatchery-raised Atlantic salmon smolt to supplement natural production in Gulf of Maine streams resulted in spawning returns of approximately 0.08% to 0.71%. The low return rate is influenced by several factors, including high mortality in the river due to downstream passage barriers and low marine survival.

Constructing Fish Ladders for Salmon Migration

Fish passage is crucial for adult salmon to travel upriver for spawning and for smolts to reach the sea. Fish ladders, or fishways, are often built to help salmon swim around dams or other obstacles that impede their progress to the spawning grounds. To aid in downstream passage, bypass structures are sometimes constructed, or water is allowed to spill over dams.

The Legacy of the Presidential Salmon

Prior to the decline of Atlantic salmon, anglers participated in an annual competition to catch the largest spring salmon. The Presidential Salmon Tradition emerged from a Penobscot River contest when, in 1912, Karl Anderson sent his 22-pound winning salmon to President Taft. This tradition ceased in 1992 due to the decline in salmon abundance, and President George H. W. Bush received the last Presidential salmon.

Thank you to Ruth Haas-Castro of the Atlantic Salmon Ecosystems Research Team for her contribution to this page.

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