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🐟 How does a salmon find its home river?

Follow salmon from freshwater to the open ocean and back as magnetic cues provide broad direction and learned river odors refine the final search.

3
lessons
~10 min
to learn
🔬 Science
subject
Adults
level
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What you’ll learn

  1. The journey begins in a riverExplain why salmon must separate ocean growth from freshwater homing and why the return journey consumes stored energy.Salmon grow at sea but must later return to freshwater spawning habitat, spending a finite energy budget along the way.
  2. Magnetic cues set the broad directionDescribe how geographic variation in Earth's magnetic field can support broad ocean navigation and why it cannot identify every tributary alone.Magnetic cues can guide a salmon toward its coastal home region, with uncertainty and field drift built into the system.
  3. Smell identifies the final streamExplain olfactory imprinting and how learned river chemistry helps salmon refine a broad route into a tributary-level return.A salmon samples changing water chemistry to recognize its home river, then pays the physical cost of reaching spawning habitat.

Questions this course answers

Why does the salmon's ocean phase make homing a navigation problem?

Salmon grow and feed in the ocean but later must locate their natal river and tributary.

What job can Earth's magnetic field perform during the oceanic part of a salmon's return?

Magnetic field values vary geographically and can support broad-scale orientation, while local cues refine the final search.

How can a salmon use both magnetic navigation and olfactory imprinting to find its home river?

The two cues work at different spatial scales: a broad magnetic map narrows the journey, while river odors provide local recognition. The fish must still spend energy passing upstream and spawning.

Grounded in trusted sources

  • NOAA Fisheries, Fish Olfaction and Homing Research, https://www.fisheries.noaa.gov/west-coast/science-data/fish-olfaction-and-homing-research
  • Bracis and Anderson, An investigation of the geomagnetic imprinting hypothesis for salmon, Fisheries Oceanography, https://doi.org/10.1111/j.1365-2419.2012.00617.x
  • Putman et al., Geomagnetic imprinting predicts spatio-temporal variation in homing migration of pink and sockeye salmon, Journal of the Royal Society Interface, https://doi.org/10.1098/rsif.2014.0542
  • NOAA Fisheries, Salmon Life Cycle and Seasonal Fishery Planning, https://www.fisheries.noaa.gov/west-coast/sustainable-fisheries/salmon-life-cycle-and-seasonal-fishery-planning
  • NOAA Fisheries, Run-timing Matters: Evolution, Plasticity, and Functional Extinction of Unique Pacific Salmon Populations, https://www.fisheries.noaa.gov/west-coast/climate/run-timing-matters-evolution-plasticity-and-functional-extinction-unique-pacific
  • Wikimedia Commons MediaWiki API, https://commons.wikimedia.org/w/api.php

Every Wunder lesson is built from real, reputable sources — never invented.

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