Acoustic tags are attached to a variety of juvenile and adult marine animals, either on their outer body surface, or more typically implanted inside their abdominal cavity. Each tag transmits a unique sound signal that identifies the individual tagged animal when it is within range of a receiving instrument that listens for the signals. Some tags can provide data on environmental characteristics that the tagged animals experience, such as depth and temperature. Other tags can measure how an animal moves through its environment through an integrated accelerometer. A hydrophone receiver picks up sound signals created by the tags and converts them to data that researchers can use. Researchers download that data either through a real-time satellite link, remotely from the ocean surface via a modem, or by physically bringing the receivers up off the ocean floor. For the more extensive study of large-scale fish movement, scientists use a series of receivers permanently placed on the ocean floor that record the acoustic signals sent by tagged animals of many different species making their journeys up and down the coast. Acoustic tags can provide information about when and where tagged individuals travel and where mortality occurs. The Census of Marine Life Pacific Ocean Shelf Tracking (POST) project is pioneering the placement of tracking arrays and the ocean tracking network has extended the listening arrays, species tagged, and geographic areas covered.
A steelhead salmon smolt being readied to receive an acoustic tag. (POST, David Welch)
POST scientists on site in one of the project's 7 river systems, tagging wild salmon smolts. (David Welch)
A juvenile salmon about to be released after being fitted with acoustic tags. (David Welch)
POST team members working on a large series of seabed nodes that they use to record acoustic signals from tagged fish. (David Welch)