Salmon have an incredible ability to migrate long distances and return to their natal streams to spawn. This homing behavior allows salmon to take advantage of abundant ocean resources while ensuring they reproduce in suitable freshwater habitat But how exactly do salmon navigate back to their birthplace after spending years roaming the ocean?
Salmon Use Multiple Navigation Tools
Research shows salmon rely on a sophisticated suite of senses and strategies to find their way back home. Some key navigation tools include
-
Smell Salmon imprint on the unique chemical signature of their home stream as juveniles before migrating to the ocean. As adults they use their acute sense of smell to identify their natal stream.
-
Magnetic fields: Salmon can detect subtle variations in the Earth’s magnetic field, allowing them to maintain a sense of latitude and longitude while at sea. Their lateral line system, which detects water movements, may sense magnetic fields.
-
Celestial cues: Salmon orient themselves using cues like the sun’s position and polarized light patterns, allowing them to maintain their bearing.
-
Water characteristics: Salmon likely use temperature, salinity, and other water cues to stay on track, especially as they near the coast.
-
Stream hydrology: The sounds, scents, and flows of their home stream become familiar signposts for salmon as they move upstream.
Salmon Imprint on Their Home Stream
A key first step in salmon homing is imprinting. As juvenile salmon prepare to migrate to the ocean, they become extra sensitive to the distinctive smells of their home stream. These odor cues get recorded in the salmon’s long-term memory.
Scientists have conducted experiments where young salmon were transferred to a new stream or hatchery before imprinting. These displaced fish often returned to the stream where imprinting occurred rather than their original stream. This demonstrates the importance of imprinting for homing.
Wild salmon that imprint in complex, natural streams seem to home more precisely than hatchery salmon imprinting in simple concrete raceways. The richness of imprinted cues may explain why wild fish stray less.
Salmon Use Specialized Sensory Systems
Salmon have specialized sensory systems tailored for long-distance ocean navigation:
-
An olfactory system with millions of scent receptors allows salmon to detect minute amounts of home stream odors in the ocean.
-
A sensitive lateral line along the body, which detects water movements and electrical fields, may sense magnetic fields for orientation.
-
Light-sensitive pineal glands in the brain allow salmon to orient using celestial cues like the sun.
-
A magnetic sense in the nasal region may detect field intensity and inclination.
-
Extra rod cells in the retina improve vision in the low-light ocean depths.
The Homing Journey Is Complex
A salmon’s return trip involves much more than just swimming straight home. Some key components of their marathon homing journey include:
-
Open ocean migration: Salmon travel vast distances in the ocean, likely using magnetic fields along with celestial cues to maintain their bearing. Smells become useful closer to shore.
-
Coastal approach: As salmon near the coast, odors from their home stream become detectable. Smells guide them towards the correct river mouth.
-
River entry: On entering the river, salmon switch to imprinted stream odors and hydrologic cues to identify their specific tributary.
-
Upstream migration: Salmon follow increasing odor concentrations upstream. They also use stream hydraulics, morphology, and water chemistry as guideposts.
-
Natal area: In the home stretch, precise imprinted odors pinpoint the exact pool or tributary where the salmon hatched years prior.
Unique Homing Challenges Exist
While salmon are amazingly adept navigators, some environments pose unique homing challenges:
-
Dams: Dams disorient salmon when they exit turbines or fish ladders. Straying above dams is common. Transporting salmon around dams helps improve homing.
-
Hatcheries: Hatchery salmon imprint on simplified environments unlike wild salmon. This may explain increased straying by hatchery fish.
-
Mixed stocks: When multiple salmon stocks intermingle in the ocean, finding the correct home river is more difficult. DNA analysis helps manage mixed stocks.
-
Ocean conditions: Unusual currents or temperatures may displace salmon migration routes, making homing less precise. However, salmon are adaptable within limits.
Homing Is Vital for Salmon Survival
The salmon’s legendary homing ability is ultimately what drives the persistence of distinct salmon stocks and their ability to populate the same streams for generations. Key reasons accurate homing is so vital include:
-
Salmon populations are adapted to their specific home streams. If salmon spawn in unfamiliar habitats, their offspring will be less fit.
-
Competition for resources is minimized when different stocks return reliably to separate spawning grounds.
-
Straying into occupied streams risks hybridizing locally-adapted populations.
-
Dependable returns allow efficient harvest management of distinct salmon runs.
In short, the salmon’s navigational prowess ensures they return to just the right place at just the right time to continue the cycle of their remarkable life history. Scientists continue working to fully understand how these fish achieve this extraordinary biological feat.
Life Cycle of Salmon
The life histories of different salmon stocks along the West Coast is diverse and complex. While all salmon exhibit the same general life cycle components, different types or stocks of salmon can vary widely in how those components actually occur, or for how long.
Adult salmon spawn in freshwater, where female salmon lay thousands of eggs that are fertilized by male salmon. Spawning can occur in spring, summer, fall, or winter and depends on the salmon species. After spawning, adult salmon die and their bodies provide nutrients for the freshwater ecosystem. Eggs are buried in gravel nests, called “redds,” and salmon can stay in their eggs for several weeks to months until they hatch. Once eggs hatch, the juvenile fish, called “fry,” can stay in the gravel nest to feed for 3-4 months. As juvenile salmon grow, they may remain in the freshwater rivers anywhere from a few hours to several years, depending on the species and other environmental factors. As juvenile salmon swim towards the ocean, they begin the process called smoltification–transitioning from living in freshwater to living in saltwater. The “smolts” may stay in estuaries from a few days to several weeks to feed, adapt, and prepare to enter the ocean.
Species of salmon can spend from 1 up to 6 years in the ocean as they mature and grow into adults. While in the ocean growing, salmon feed on small fish, squid, eels, and shrimp. When salmon are ready to reproduce, they migrate from the ocean back into freshwater rivers and streams to their spawning grounds. On their journey, they may encounter rapids, waterfalls, predators, and hydroelectric dams. Once salmon reach their freshwater spawning grounds, females dig a gravel nest, and the life cycle begins again.
Considerations in Fishery Plans Image
Juvenile Coho Salmon. Credit: David Stafford/NOAA
Learning about the life cycles of salmon and steelhead, the different ages of when they return, times of year and migration patterns, can help fishery managers target specific stocks and forecast the abundance of fish available in each fishery. Different salmon and steelhead life histories require different methods to estimate their abundance. The estimated abundance is used to regulate salmon fisheries and accurately plan the management of fisheries to ensure salmon stocks are managed sustainably.
The variety of movement and ages of salmon and steelhead can make them more vulnerable to environmental changes and stressors at different times of year, impacting their survival. Salmon and steelhead species with diverse life histories, with multiple ages returning to spawn, may be more resilient to climate and habitat changes because the generations of their species are spread over several years. In contrast, salmon species, such as coho and pink salmon, that return at consistent ages, may be more susceptible and impacted by catastrophic events, leading to the loss of whole generations of fish. With an understanding of salmon and steelhead reaction to stressors, management plans can be created that consider the size of fisheries, and aim to balance ecological and economic objectives.
How Do Salmon Find Their Way?
FAQ
How do salmon find their way back to spawn?
As salmon migrate and feed in the dark blue ocean, they sense minute variations in the magnetic field to determine their location. As if salmon weren’t fascinating enough, recent studies have shown slight natural movement (drift) of the earth’s magnetic field causes slight shifts in migration route of returning salmon!
Do salmon always return to where they were born?
Do salmon return to spawn in freshwater areas where they were born? 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.
What triggers salmon to spawn?
“Pheromones at the spawning grounds [trigger] a second shift to further enhance reproductive loading.” The salmon also undergo radical morphological changes as they prepare for the spawning event ahead.
How do salmon know where to lay eggs?
It is unknown how exactly salmon detect their natal streams, though it is suspected that scents and chemical cues, as well as the sun, play an important role in the homeward migration. Once the salmon reach freshwater, they stop feeding. During the course of the journey, their bodies instinctively prepare for spawning.
Why do salmon come back to the stream where they were born?
Salmon come back to the stream where they were ‘born’because they ‘know’ it is a good place to spawn ; they won’t waste time looking for a stream with good habitat and other salmon. Scientists believe that salmon navigate by using the earth’s magnetic field like a compass.
How do salmon know where their home is when they return?
How do salmon know where their home is when they return from the ocean? Salmon come back to the stream where they were ‘born’ because they ‘know’ it is a good place to spawn; they won’t waste time looking for a stream with good habitat and other salmon. Scientists believe that salmon navigate by using the earth’s magnetic field like a compass.
Why do salmon come back to the same stream?
Salmon come back to the same stream they were “born” in because they “know” it is a good place to spawn and they won’t waste time looking for another stream with good habitat and other fish to spawn with. Why are there so few salmon left?
Why do salmon spawn back to spawn?
Years later, when the salmon head back home to spawn, they home in on that pattern. In a study published Thursday in Current Biology, the scientists behind that theory now say they have evidence that’s exactly how the fish are navigating.
How do salmon spawn in the same stream?
Salmon can migrate out to sea to feed for several years before returning to spawn in the same stream, sometimes even the same section of stream, in which they were born. Other homing species probably use similar mechanisms, but few can match such precision. How salmon return to the correct shoreline region is not completely understood.
When do salmon spawn?
Once they have completed their migration to the ocean, the salmon grow rapidly and mature into adults. Adult salmon spend several years in the ocean, feeding on small fish and other marine organisms, before returning to their natal stream or river to spawn. When the adult salmon return to their natal stream or river, they are called spawners.