One of the most revolutionary technologies designed to track aquatic species is acoustic telemetry. This method of tracking allows scientists to monitor the movement of organisms beneath the water surface. At the Smithsonian Institution, scientists use acoustic telemetry to study marine organisms like sharks and rays. This groundbreaking technology uses acoustic transmitters and receivers to follow tagged individuals as they move throughout the Chesapeake Bay and along annual migrations around the world.

Once a target species has been selected, Smithsonian scientists find a suitable individual and tag it with an acoustic transmitter. This transmitter sends out unique high frequency pulses, which are recorded when a tagged individual passes within range of a receiver. Sound travels four times faster in water than air, which make it possible for receivers to detect the unique codes. The receivers convert the sound into data that Smithsonian scientists use to determine the organisms location and identity. More receivers means more data and a better estimate of how organisms move. As a result, receivers are often established in arrays to provide fine-scale data about the movements of organisms.

Graphic of marine tracking sharks


What makes this technology so revolutionary is its ability to track fish that were previously difficult to study. Another method of tracking marine organisms is to use GPS tags. GPS tags, however, rely on the organism coming to the surface for a certain amount of time in order to transmit its location to a satellite. This is an effective method for studying marine mammals that have to come to the surface to breathe, but less consistent for fish, that don’t have to come to the surface at all. Acoustic telemetry functions entirely underwater, allowing scientists to track species that rarely or never come to the surface.

The dependence on receiver presence throughout the entire study area of the species is perhaps the biggest limitation of this method of tracking. Acoustic telemetry not only requires some existing knowledge of the tagged individual’s movement range, but also requires an effective array of receivers in that area. Smithsonian scientists ran into this problem when studying Blacktip Sharks. An individual was tagged in the Chesapeake Bay, but as it moved down the coastline the individual didn’t register on another acoustic array until it reached Charleston, SC. Because of the lack of receivers along the individuals path, the exact pathway that the individual took is unknown. Luckily, as acoustic telemetry becomes a more widely practiced method of research, more receiver arrays will be deployed to provide more complete data on the movements of individual organisms.

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