Do Oceanic Fish 'Migrate'?

Yes. Certain sharks migrate large distances to feed and breed, in fact that is often the purpose of shark tagging programs, to determine the interconnectivity of populations. It's difficult to provide fisheries and conservation estates with details of a population, if that population is thought to only exist in X, while it actually exists in X, Y and Z. If you fish out Z and Y you might find that your protected area, X, has no fish. Billfish (Marlin, Swordfish, Sailfish) also migrate to find waters that are warm enough to rest in, as these are fish that dive to great depths and often have to spend time on the surface warming up their bodies (their head regions are warmed endothermically, but their bodies are not) before diving again. Tuna also make long distance migrations to breed, with mediterranean Bluefin Tuna migrating into the main Atlantic Ocean to breed before migrating back. Yellowfin Tuna also migrate and while I can't remember the locations, they are often highly lucrative for local fishermen.

Most migration occurs as a result of life cycle. In South Africa, Red Steenbras are found to migrate up the East coast as they get older and stay there. Thus, there is much more recruitment into one area than another and this is important for managing the fishery. Atlantic Squid use the Gulf stream to transport their young from the Gulf of Mexico after having bred, where they will slowly develop in the current and arrive in the productive temperate waters off the coast of Canada once they are old enough to survive the cold - once this generation of squid are strong enough they swim back to the Gulf of Mexico on deepwater currents and repeat the cycle. Freshwater Eels make use of many different currents in both the Atlantic and the Pacific to ensure they make it to their breeding grounds and the young make it back to the terrestrial habitats they came from. Both Eels and Squid are semelparous (meaning they breed once, then die) though so these migrations are not yearly, they only happen once.

/r/askscience Thread