Salmon have an incredible ability to migrate hundreds or even thousands of miles from the ocean back to the exact river or stream where they were born to spawn. But how do these fish manage to find their way back home with such pinpoint accuracy?
Salmon Use Multiple Navigation Tools
Scientists believe salmon rely on a sophisticated suite of sensory capabilities and navigation mechanisms to guide them on their epic journeys. Some of the main tools salmon use include:
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Scent imprinting – When juvenile salmon reach the smolt stage and prepare to migrate to the ocean, they imprint the unique scent of their home stream. As adults, they rely on their acute sense of smell to identify chemical cues that lead back to the same waterway.
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Celestial navigation – Salmon likely use cues from the sun, moon, stars, and polarized light to determine their position and direction of travel while navigating in the open ocean.
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Magnetic senses – Salmon can detect the Earth’s magnetic field and use it as a compass to orient themselves in the right direction The magnetic signature of their home river helps guide them
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Temperature and salinity – Salmon may use temperature and salinity gradients as they transition from saltwater to freshwater to pinpoint river and stream locations.
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Instinct – Salmon have an innate drive to return to freshwater habitats to spawn that kicks in when they reach sexual maturity.
So salmon integrate information from multiple senses and navigation systems to accomplish their homing migrations. But two mechanisms, in particular, stand out as crucial – scent imprinting and magnetic senses.
The Importance of Smell Imprinting
Experiments have shown that the olfactory imprinting salmon undergo as juveniles is critical for guiding the fish back to their natal streams as adults. In one study, young salmon reared in a hatchery and then moved to a different stream before migrating imprinted on the scent of the second stream. As adults, most returned to this transplanted stream rather than their actual stream of origin.
This demonstrates that the unique chemical signature salmon learn as smolts becomes their homing target. Adult salmon rely heavily on scent cues from amino acids, bile salts, and other compounds specific to their home waterway that they remember from the smolt stage. Their olfactory system can detect the faint traces of this familiar scent even amidst all the other river smells.
Salmon may imprint on scent during multiple early life stages including hatching, emergence from gravel nests, and smolting. This helps them map out the chemically distinct identity of their local waters before migrating. Hatchery fish imprint on simpler environments and have a poorer scent map, which is why they often stray off course when returning to spawn.
Magnetoreception Guides Ocean Navigation
While smell imprinting explains how salmon follow scent breadcrumbs back to their specific river and tributary, their magnetic senses help guide long-distance travel through open water.
As they roam the ocean and prepare to return home, salmon detect subtle differences in the magnetic field strength and inclination angle around coastal regions. The particular geomagnetic signature near their home river provides a magnetic map they can follow.
Scientists think salmon have magnetite crystals in their noses or lateral lines (sensory organs running down their bodies) that give them this magnetic sense. By matching the magnetic field cues they perceive with the imprinted signature of their home territory, salmon find their way back from distant ocean feeding grounds.
Interestingly, human infrastructure like dams and powerlines that produce magnetic fields can interfere with salmon’s magnetoreception. This suggests why some hatchery-raised salmon have trouble returning – they fail to properly imprint on a natural geomagnetic map.
An Integrated Navigation System
So salmon have a toolkit of different senses, instincts, and navigation abilities they use together when migrating to their spawning grounds. Smell imprinting dials them into their home river, while magnetic senses provide coarse positioning during ocean travel. Other cues like celestial navigation and salinity gradients help too.
And salmon aren’t just relying on inherited behaviors and imprinting. They also learn and update their mental maps of home rivers each migration. It’s this flexibility combined with multiple sophisticated navigation senses that enable salmon to perform their incredible marathon migrations with high accuracy year after year.
To summarize key points:
- Salmon use smell imprinting of natal waters plus magnetoreception of geomagnetic fields to navigate back home to spawn
- Olfactory imprinting as juveniles gives salmon their unique homing scent target
- Magnetic sensing helps salmon determine position and direction in the open ocean
- An integrated toolkit of navigation abilities allows precise homing migrations
- Interference with natural magnetic fields may disrupt salmon navigation
The homing migration of salmon is a wonder of the animal world. Understanding how salmon accomplish these feats reveals fascinating aspects of fish sensory biology, navigation, and the innate drive to return to their birthplace to breed. While some details remain mysterious, scientists continue making progress unraveling the secrets behind the salmon’s extraordinary orientation and tracking abilities.
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.
Pacific Salmon and Steelhead Life Histories
Salmon and steelhead can return from the ocean to their freshwater habitats to spawn at any time of the year. Migration times and distance can fluctuate greatly within species. The fish “runs” may differ by species, seasons, and locations (though most of these fish return to the streams where they were born). This information is essential for fisheries managers to estimate population sizes, harvest amounts, and design fisheries management plans. When planning and managing fisheries, predictions about the different ages of returning fish, population sizes, and escapement objectives are considered. The variability in ages of returning salmon affects how many return each year and is an important consideration in estimating how many salmon will return to spawn each year, and to estimate the stock and harvest amount for the season. The analysis and evaluation of the potential number of salmon in the fishery is therefore complicated due to the various ages when salmon return.
Some fish may migrate far, some species may stay in the rivers for a long time before spawning, and other fish may be quick to return and spawn. The list below describes different salmon and steelhead species, and life cycle information used in fisheries management.
Pink salmon are one of the fastest growing Pacific salmon species. After about 18 months in the ocean, pink salmon have reached maturity, and return to freshwater to spawn. Spawning occurs from August to October, when pink salmon are adult two-year-olds. Pink salmon mature and complete their life cycle in 2 years and this consistency has created distinct odd-year and even-year populations to use in planning their fisheries.
Chum salmon. Credit: NOAA Fisheries
Chum salmon are usually the last of the Pacific salmon that return to freshwater to spawn. After 3 to 4 years in the ocean, chum salmon reach full maturity and migrate back to their spawning grounds. Chum salmon spawn from generally late October to March, with peak spawning in early winter when the higher water flows in rivers. However, in some areas they can return as early as August. Chum salmon complete their life cycle between 3 to 6 years. The variety in ages of returning chum salmon is important when estimating population sizes and harvest amounts for fishery plans.
Sockeye salmon. Credit: NOAA Fisheries
Sockeye salmon mature and return to spawning grounds after 2 – 3 years in the ocean; some may stay longer and return after 4 – 5 years. Sockeye salmon spawn from July to late October when they are mature. Their lifespan is usually about 5 years; however, in the Pacific Northwest, sockeye salmon lifespan is more commonly 4 years. By understanding the general age of returning sockeye salmon, fishery managers can predict stock sizes and develop fishery proposals.
Chinook Salmon. Credit: Michael Humling/USFWS.
Chinook salmon can spend from 1 to 6 years growing in the ocean. Chinook salmon mature between the ages of 2 to 7; however, they are usually 3-4 years old when they return to spawn. The timing of when Chinook salmon migrate from the ocean to their spawning grounds divides Chinook salmon into four distinct population “runs”. These distinct populations are named for the season when most of the fish run return from the ocean to spawn: spring, summer, fall, or winter. Some Chinook salmon enter freshwater from the ocean and are ready to spawn soon after entering freshwater. Others come from the ocean and need to spend time maturing in freshwater before they are ready to spawn.
The distance and time it takes for Chinook salmon to migrate to their spawning grounds can range from relatively short to very long depending on the population. Knowledge of the varying distinct Chinook salmon populations, ages, and migration patterns can assist fishery managers in the estimation and reconstruction of populations, and plan fisheries.
Spring-run Chinook salmon return to their spawning grounds at different ages, from 3 to 5 years of age. The migration from the ocean to their spawning grounds begins in April through July, with peak migration occurring in May. Spawning begins in August and continues through early November.
Summer-run Chinook salmon may return to their spawning grounds from 2 to 5 years of age. Traveling back to their spawning grounds occurs from June to August. Spawning begins in late August until November.
Fall-run Chinook salmon are the most common group of Chinook salmon on the West Coast. Most fall-run Chinook salmon can spend 3-4 years in the ocean before migrating to their spawning grounds, however some can return at 2 or 5 years old. The journey to spawning grounds begins in late July, peaking in September, and ends in December. Spawning happens from October through December. The most common age of returning and spawning adults is 4 years old.
Winter-run Chinook salmon may return to their spawning grounds after 1 to 3 years in the ocean. The migration to their spawning grounds occurs from December through May, with peak migration in March. Spawning occurs from mid-April to early August.
Coho salmon. Credit: NOAA Fisheries
Coho salmon remain in the ocean for about 18 months to 2 years, and begin their migration back to spawning grounds from September through December. Coho salmon spawn in November and December, and the lifespan of coho salmon is usually 3 to 4 years. However, some male coho reach maturity early and migrate back to freshwater streams as 2-year-old “jacks.” The “jack” returns may provide an estimate of adult abundance for the following year and assist in fishery plans.
Male and female steelhead. Credit: NOAA Fisheries
Steelhead can spend from 1 to 4 years in the ocean before traveling to their spawning grounds. There are two general types of steelhead runs, named for the season when most of the fish run return from the ocean: winter and summer.
Winter-run Steelhead return from the ocean at age 4 or 5 years, and travel to their spawning grounds from November to April. Winter-run steelhead are very mature fish and begin spawning soon after they arrive.
Summer-run Steelhead usually return from the ocean at age 3 and migrate to their spawning grounds from April to September. The summer-run steelhead are typically immature fish and need several months of maturing in the freshwater before spawning.
Both steelhead stocks spawn from winter to early spring (January to April). The lifespan of steelhead varies from 5 up to 11 years.
Steelhead are different from Pacific salmon because steelhead do not all die once they spawn. Steelhead can survive after spawning and can migrate to the ocean and back to their spawning grounds again in the future, laying eggs more than once in their lifespan. The seasonal differences in steelhead migrations and multiple trips to spawning grounds are considered when predictions are made about the number of returning steelhead for the season and their fisheries management.
Learn more about Pacific salmon on the West Coast:
How do salmon travel between rivers and the sea? | AI | Full Documentary
FAQ
FAQ
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.
How do fish know where they are going?
Scientists believe that salmon navigate by using the earth’s magnetic field like a compass. When they find the river they came from, they start using smell to find their way back to their home stream. They build their ‘smell memory-bank’ when they start migrating to the ocean as young fish.
What triggers salmon to run?
One theory is that there are geomagnetic and chemical cues which the salmon use to guide them back to their birthplace. The fish may be sensitive to the Earth’s magnetic field, which could allow the fish to orient itself in the ocean, so it can navigate back to the estuary of its natal stream.
How do salmon detect magnetic fields?
A new study into the life cycle of salmon, involving magnetic pulses, reinforces one hypothesis: The fish use microscopic crystals of magnetite in their tissue as both a map and compass and navigate via the Earth’s magnetic field. Findings were published in the Journal of Experimental Biology .
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.
How do salmon find their way?
This behavior is best exemplified by salmon, which combine conventional open-water navigation and a keen sense of smell to find their way. 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.
How do salmon navigate?
Scientists believe that salmon navigate by using the earth’s magnetic field like a compass. When they find the river they came from, they start using smell to find their way back to their home stream. They build their ‘smell memory-bank’ when they start migrating to the ocean as young fish.
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 live?
To be a salmon is to live an adventurous life: They hatch in freshwater streams, travel miles downstream to the ocean, and live years dodging predators in the open sea. But in order to reproduce, they must return back to that mountain stream, however far away. How do they find their way?
What happens if a salmon can’t find a stream?
They build their ‘smell memory-bank’ when they start migrating to the ocean as young fish. If a salmon can’t find its stream, some continue to search for the right stream until they use up all their energy and die, but most simply try to find other salmon with which to spawn.