Scientists want to know as well. That's why NOAA provides fishermen with tags to put on fish they catch and release, including highly migratory species like tunas, sailfish, and marlin. After tagging a fish, they send the tag number to NOAA Fisheries, along with date, location, length and weight. If the fish is recaptured, the fisherman can read the number and call it in. That allows scientists to track migration patterns and estimate growth and mortality rates for these valuable species.