Acoustic Tagging is often referred to as telemetry, which simply means measuring from a distance. Acoustic telemetry allows scientists to repeatedly locate and track tagged fish in remote or inaccessible settings, thus providing a more detailed look at fish movement patterns, habitat usage and behavior related to seasonal and environmental changes.
Acoustic tags are based on the principles of SONAR (sound navigation and ranging), originally developed to detect submarines in WWI. The earliest study using acoustic telemetry in fish was in 1956 to observe the behavior of salmon passing through a dam on the Columbia River in Oregon. Acoustic telemetry technology has advanced over time to reduce the size and improve the effectiveness of all the various components.
Acoustic tags, or transmitters, are considered active tags, meaning they contain their own energy source. Once activated, the battery-powered tag emits a signal at short, random intervals in the acoustic frequency range (specific wavelengths) . Tags are surgically implanted into the body cavity of fish and can emit an acoustic signal for up to two years. Acoustic signals can travel a long distance underwater (up to half a mile away) and can be detected by listening stations called hydrophones. The detections can either be picked up remotely through active tracking or by passively tracking using stationary receivers that constantly listen for a tagged fish to swim by. The receivers collect and store the detections which are routinely downloaded by biologists using Bluetooth technology. The downloaded detections include information about the date, time, unique fish ID and for some larger tags even depth and temperature.
From whale sharks in the Gulf of Mexico to speckled trout in Lake Pontchartrain, follow these species and more using our Fish Tracker.
Past Telemetry Projects
Calcasieu Lake
In 2007, the Department undertook a cooperative study with Louisiana State University to investigate speckled trout in Calcasieu Lake. Located in western Louisiana, the lake is approximately 300 square kilometers with limited points of entry and exit. Sixty receivers were deployed to passively listen for the 172 acoustically tagged speckled trout. This information was supplemented with active tracking and analysis of conventional tagging data from the area. Researchers analyzed the data after two years and found that the trout preferred deep channels during cold fronts and storm events. Female trout avoided areas that were low salinity, and did not leave the lake as often as males.
Bayou St. John
Also in 2007, the Department began a cooperative study with the University of New Orleans on redfish. Bayou St. John is located in New Orleans and was historically connected to Lake Pontchartrain. Until recently, the bayou had a dam that blocked fish from passing from the lake into the bayou. For the study, redfish were captured elsewhere and acoustically tagged and released into the bayou. Four receivers were deployed in the 4-mile bayou to detect the 29 tagged redfish. Data was collected for approximately 5 years and analyzed to determine how the fish behaved and if they could survive in the bayou. Researchers found that these redfish preferred the northern area of the bayou and were able to survive in this waterbody.
Ongoing Telemetry Projects
Lake Pontchartrain
Beginning in 2012, the Department chose to focus specifically on Lake Pontchartrain in an effort to test the capabilities of acoustic telemetry in a large system. Lake Pontchartrain is located north of New Orleans and encompasses 630 square miles, more than double the size of Calcasieu Lake. Building on what was learned in the Calcasieu Lake study, a total of 90 receivers were deployed in an array to cover many different habitats and points of entry and exit in the lake. The collaborative study uses the telemetry array to cooperatively monitor species acoustically tagged by different researchers.
The initial efforts focused on a total of 211 speckled trout tagged by researchers from LSU. The array has recorded over 1.5 million detections, which is an extremely large amount of data to process. Final results are still being analyzed, but preliminary indications are that approximately 25 percent of the fish have left the lake, with some returning in later seasons. Data also shows a movement shift of trout toward the eastern, saltier portion of the lake when there is a drop in salinity. Stay tuned for the final results from this study.
Building on the redfish study in Bayou St. John, UNO also tagged and released 18 bullsharks from Lake Pontchartrain in 2013. All of the bullsharks captured were fairly young, and two were estimated to be approximately a month old due to visible umbilical scars. Initial data analysis showed that these sharks leave the lake when the temperature drops below 68°F in the fall or winter, and the sharks return when the temperature rises above that threshold in the spring. These sharks are still being tracked, and we look forward to seeing how many return this spring.
Currently, the Department is tagging redfish and speckled trout in the lake. In the fall of 2014, 28 redfish and 3 trout were tagged and added to the telemetry network in Lake Pontchartrain. Tracks and data from all tagged fish will be available on the website soon.
In addition to the fish that have been tagged within the lake, LDWF receivers frequently hear fish on the receivers that have been tagged by other institutions outside of Lake Pontchartrain, such as Gulf sturgeon tagged by the US Army Corps of Engineers, U.S. Fish and Wildlife Service and the University of Southern Mississippi’s Gulf Coast Research Lab. These institutions have also detected our fish moving near their receivers. Data is cooperatively exchanged between institutions, and researchers are able to receive valuable information about their tagged fish locations that they otherwise would not have known.
Three additional receivers were deployed in the Lake Pontchartrain Basin in 2015. The Department plans to continue to improve upon the Lake Pontchartrain array by extending receivers further out into the basin to give an expanded view of acoustically tagged fish movements.
