Acoustic Fish Tags
22Acoustic fish tags are used to monitor and track fish movements. Small tags are surgically implanted, injected, fed (via baited fish), or externally attached to a fish. The tags transmit a high frequency “ping” which can be heard as far as half a kilometer away. Acoustic receivers are strategically placed around the area of interest to listen for these pings. The receivers can be placed on anchored buoys, cabled underwater arrays, or existing oil and gas platforms, as well as integrated into ocean gliders, or even carried by other marine animals, such as elephant seals.
As acoustic signals from tags are detected and recorded by the receiver array, travel time can be calculated, and the fish’s location pinpointed. The accuracy of this method depends on the position of the tag relative to the receiver(s), the background noise (ambient noise) level relative to the frequency of the ping, and the accuracy of the assumed speed of sound in water. Tagged individuals can be tracked for periods ranging from days to years. Study durations are determined by tag battery life, attachment method, and data resolution/complexity.
A common application of acoustic telemetry is to investigate animal behavior and survival. Atlantic salmon are anadromous fish that migrate between freshwater spawning and nursery habitats to ocean feeding grounds. Historically, they were found in North American waters from Long Island Sound in the United States to Ungava Bay in Northeastern Canada. Dams, pollution, overfishing, and other factors led to significant declines in the wild Atlantic salmon stock: by the mid-20th century, the primary distribution of Atlantic salmon in the U.S. was limited to just a few remnant populations in the eastern third of Maine’s coast. Despite conservation efforts, returns of Atlantic salmon to natal rivers remain low. Using acoustic telemetry, scientists and managers can monitor the movement of tagged Atlantic salmon juveniles (“smolts”) as they migrate from rivers, through estuaries, and into the nearshore marine environment. Data gathered allow for a better understanding of the timing and duration of migration, routes of travel, areas used for holding and rearing, and locations of high mortality. This information can then be used to estimate abundance, evaluate mitigation efforts, and improve conservation plans. Similar research and management regimes are being implemented for Pacific populations of endangered salmon and steelhead, whose migration behavior and survival rates have been significantly impacted by the installation of hydroelectric dams in their natal rivers.
It is important to note that many marine predators, including fish and marine mammals, prey upon tagged juvenile salmon, and this complicates survivorship estimates determined through acoustic telemetry. Studies have shown pinnipeds to detect and selectively target fishes carrying high frequency acoustic tags. Other research has shown the characteristics of emitted pings to change post-predation event, and scientists may be able to use this data to correct survivorship estimates.
Acoustic telemetry can also be used to assess multispecies movements. Tagging data can help managers evaluate the functionality of marine protected areas (MPAs) delineated to help rebuild depleted coral reef fish populations. Acoustic tags have also been used to track and monitor the behavior of several elasmobranch species, including tiger sharks, blue sharks, manta rays, and great white sharks. Data reveal distinct patterns of habitat use and movement of animals not previously identified. Tagged great white sharks in South Africa were detected in all months and across all years in South Bay, however, their use of the Bay varied significantly with season and the sex of the shark. In autumn and winter, animals of both sexes aggregated around a Cape fur seal colony at Seal Island. In spring and summer, females frequented inshore areas (not associated with seal colonies), while males were seldom detected acoustically. In addition to defining habitat associations for this population, the finding that female sharks aggregate in inshore regions, not associated with seal colonies, during periods of high human, recreational use (spring/summer) highlights the need for ongoing shark-human mitigation strategies in this area.
Additional Links on DOSITS
- Steig and Ehrenberg, 2002, “A Method for Estimating the “Position Accuracy” of Acoustic Fish Tags.” ICES Journal of Marine Science, 59: 140-149.
- HTI, Acoustic Tags to Track Fish.
- NOAA Fisheries, Northeast Salmon Team (NEST)
- NOAA Fisheries, Northeast Salmon Team (NEST) Telemetry Fact Sheet.
- Dalhousie University, Ocean Tracking Network.
- The Census of Marine Life, Pacific Ocean Salmon Tracking (POST)
- Steig, T.W., 1999, “The Use of Acoustics Tags to Monitor the Movement of Juvenile Salmonids Approaching a Dam on the Columbia River.”