Super cool breaking news! Researchers at Oregon State University have shown that salmon use MAGNETISM to find their way back to freshwater rivers to spawn! This is really cool for multiple reasons, first because while we know that salmon return to the exact streambed they were originally hatched from via chemical cues (odors), we never knew how they found the general location of the river on a larger scale. When they are born they imprint on the unique smell signature of their specific little nook of the freshwater world in order to find it within short distances (which is cool enough on its own), but the recent study has found that they also imprint upon the magnetic signature of that spot as well! This basically refers to (from my understanding) the fact that each spot on Earth is uniquely situated in relation to our planet's magnetic poles. Many other animals have been shown to use the Earth's magnetic fields for general orientation (many migratory birds, sea turtles, salamanders, frogs, even bacteria!), but this is the first evidence that salmon use it, AND the first evidence that magnetic signatures can be learned, or "imprinted". This magnetic signature is how they locate one infinitesimally small rivermouth along the relatively vast expanse of ocean and coastline, and begin the journey back to their spawning grounds - where the females release thousands of eggs, the males release lots of sperm, and they all promptly kick the bucket. Literally going out with a bang!!
Here's the link to NSF's press release about the study if you want to read more. Hope you all have a wonderful weekend!