Tracking Diadromous Fishes at Sea: The Electronic Future Using Hybrid Acoustic and Archival Tags
Michael J. W. Stokesbury, Michael J. Dadswell, Kim N. Holland, George D. Jackson, W. Don Bowen, and Ronald K. O’Dor
Abstract.—Tagging fish with electronic tags can provide information on movement, migration, behavior, and stock structure while diadromous species are at sea. The state of the art technology for tracking fishes in the marine environment includes two families of tags. Archival tags store data and either relay them to satellites or require recapture for interrogation. Low return rates for diadromous species make these tags very expensive to use. A second type, acoustic tags, sends signals to passive receivers. Information is collected from the fish only when it is within range of a receiver. Technology is now being developed to mesh these tags into a fully integrated tag that will permit archived data to be transmitted acoustically over multiple frequencies to receivers allowing data retrieval without recapturing the animal. The new technology includes a “business card” tag that is a miniaturized receiver coupled with a coded pulse transmitter. These tags will exchange and record individual-specific codes when two animals carrying them come within acoustic range of each other, which will allow data from many animals to be moved ashore through few animals. These devices would be ideal for quantifying the degree of school fidelity (or, conversely, mixing) or the degree of at sea interaction of fishes from different river systems and provide ecological information to enhance management in an ecosystem approach to fisheries.