Tools of the Trade: Telemetry

Biologist uses radio antenna to track tagged sturgeon.

Here’s a tough question. How do we know where fish go or which underwater habitats they prefer when they are out of sight? Biologists have developed some special techniques to monitor fish and track their whereabouts. One method that helps biologists monitor fish populations is telemetry, which is the process of obtaining data remotely by implanting a radio or acoustic transmitter in an animal.

Radio Tagging Muskellunge in the Potomac
The northern Potomac River is an angler’s paradise. Running through the mountains of Western Maryland, numerous freshwater species thrive here. The muskellunge, commonly called the muskie, is one of the largest freshwater game fish in North America. It is not native to Maryland but has settled into the Washington County portion of the Potomac, where it is able to naturally reproduce. This trophy fish has a reputation for eluding anglers but biologists keep tabs on the muskie’s movement and habitat preferences with radio telemetry.

Each muskie caught for tagging is surgically implanted with a small radio transponder. An incision is made on the belly of the fish, the transponder is inserted, and the incision is stitched back up. The process is quick, taking less than three minutes to complete. Each of the transponders can last upwards of five years and operates on a slightly different frequency so individual muskies can be tracked.

Using an omnidirectional antenna, biologists can track Potomac River muskie either on foot or by car. These data are being used to figure out how warm water is affecting this cold-water species. The project will help to direct habitat management and protection.

Surgically implanting acoustic tag into sturgeon

Acoustic Tagging Atlantic Sturgeon
The Atlantic sturgeon is a prehistoric fish that is estimated to have evolved millions of years ago. This species was once abundant in the Chesapeake Bay’s tribal tributaries during spawning season, but an appetite for surgeon roe caused the species to be fished to near-extinction. Now protected under the Endangered Species Act since 2012, this iconic “living fossil” is on the rebound. Several Chesapeake Bay tributaries have seen sturgeon reappear and populations grow. Scientists know more about this species thanks to telemetry.

Sturgeon migrate over a wide range of salinities in the course of their lifetimes. They hatch in freshwater rivers, head to the salty Chesapeake Bay and Atlantic Ocean as juveniles, and return to their river birthplaces to spawn annually as adults. Fisheries biologists use acoustic tagging to answer many questions about the lives of sturgeon, including determining spawning locations and habitat preferences and describing migration corridors and the timing of spawning runs into and out of the Chesapeake Bay. Acoustic tags and receivers emit and sense high frequency ultrasonic sound waves and are used for saltwater species because higher salinities impair radio signal transmission.

The acoustic tags, which have a 10-year lifespan, are implanted surgically into sturgeon and programmed to emit an individual “ping” signal every 70-150 seconds. The signal is logged by a passive receiver, which can detect signals at a range of about a kilometer. Receivers are placed on piers, dedicated buoys, and U.S. Coast Guard pilings in strategic locations. Data are retrieved periodically in the field via laptop computer and bluetooth connection.

Sturgeon researchers from Canada to Florida use the same technology and exchange tracking data freely through the Mid-Atlantic Acoustic Telemetry and Observation System, which feeds into a global monitoring network that collects detection data from the world’s five oceans.

Article appears in Vol. 23, No. 2 of the Maryland Natural Resource magazine, summer 2020.