How do spawning fish navigate back to the very same stream where they were born?
Megan McPhee, research assistant professor at the University of Montana’s Flathead Lake Biological Station, steers us to an answer: 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. 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. It appears they use some form of “map and compass” navigation based on information about position and direction of travel. This information most likely comes from a suite of environmental cues, including day length, the sun’s position and the polarization of light that results from its angle in the sky, the earth’s magnetic field, and water salinity and temperature gradients. Whatever th
