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October 25, 2001

Sensitive Sharks

Do radio transmitting tags effect a sharks senses?

Q: I watched, on the Discovery Channel, a research group in Australia tagging whale sharks with transmitters and following them. I was wondering if anyone had any information on the possibility of sound waves from the tag affecting the fish's sense of feeling or sound detection, since sharks have ampullae of Lorenzini, which have been reported to sense electricity, temperature and pressure. - Mike Picano Jr., Fort Pierce, Florida

A: Fishes' senses are very complicated, since they possess several sense organs humans lack. One organ particular to sharks is the ampullae of Lorenzini - tiny pits on the head and snout which are sensitive to weak electrical and magnetic fields. Fish easily detect small changes in temperature and pressure as well, but neither of these senses nor the sense of sound are particularly associated with the ampullae of Lorenzini.
Sound, to humans, is simply a range of vibrations passing through air or water in frequencies detected by the human ear. Lower frequencies or vibrations are detected by touch. Fish detect higher frequencies through their labyrinthine system, consisting of semicircular canals and otoliths, comparable in function to our inner ears. In low frequencies, fish are even more sensitive than humans, having an entire specialized sensory system known as the lateral line just for that purpose.
Getting back to acoustic transmitters attached to whale sharks and other fish - these devices transmit signals in a limited frequency range audible to the human ear and require a person using headphones listening to an underwater microphone. The signal may be audible to the fish as well, but shouldn't adversely affect the lateral line or labyrinthine systems.
However, in the specialized case of sharks, their ampullae of Lorenzini should detect the electrical current powering the transmitter itself, which may indeed have some effect on that sense.
In any case, the batteries used in these particular transmitters generally have a limit of a few days, and the transmitters themselves are usually programmed to detach themselves from their hosts after a set time period.