Dolphins and porpoises rely on sound to make a living in the ocean. To them, hearing is their most important sense. Dolphins and porpoises project sound, called echolocation clicks, and listen for echoes coming back from objects the sound encounters in the environment. This process, which is a form of biological sonar, is used for navigation and hunting food. But if a dolphin cannot hear, then it cannot use the echoes that return to it for these purposes. Because hearing is so critical to the livelihood of a dolphin, hearing tests have become increasingly common in the evaluation of stranded dolphins undergoing rehabilitation.
The National Marine Mammal Foundation has been working with the National Marine Fisheries Service to ensure that toothed whales undergoing rehabilitation are tested for adequate hearing prior to a determination of release. Foundation personnel travel to rehabilitation facilities, but more recently, the Foundation has been training stranding network personnel to perform the tests themselves. The stranding network personnel are provided with the equipment and know-how to perform the tests and receive yearly training from the Foundation to ensure that testing capabilities are kept at their optimum.