- Pacific Northwest National Laboratory researchers have developed the first self-charging tracking tag, an implanted acoustic transmitter that harnesses energy from the swimming animal bearing it, for studying fish behavior throughout the organisms’ lives.
- The scientists hope the tag will help us better understand long-lived and migratory species of concern, as well as comprehend and mitigate the ramifications of dams and marine energy on fish movement and survival.
- The team will field-test the tag on white sturgeon in the Columbia and Snake rivers next year.
Piezoelectricity has nothing do with pie. In fact, it’s a pioneering avenue of research into producing energy from physical movement, which could revolutionize the way we track fish.
By harnessing this source of power, the Department of Energy (DOE)’s Pacific Northwest National Laboratory (PNNL) has developed the first self-charging tag for studying the movement of fish throughout their lives. Because it works as long as the fish swims, its developers believe the technology could be especially useful for the long-term monitoring of the behavior of long-lived species like sturgeon and migratory species of concern like eels and lamprey.
“It could help us better understand how dams and ocean energy devices affect fish behavior by tracking them long-term and develop mitigation measures accordingly,” said corresponding author Daniel Deng, Chief Scientist in the Hydrology Group of Energy & Environment Directorate at PNNL.
The device consists of a supple strip of piezoelectric composite beam, a circuit board and a beeping transducer that converts energy from one form to another. Underwater receivers record these sounds to keep track of the fish. The tag has been designed in 10 cm and 7.7 cm lengths to fit fish of various sizes; it weighs about 1 g and 0.8 g, respectively. The transmitter emits a signal that provides more than 65,000 unique tag codes and is strong enough to be detected up to 100 meters away.
According to the researchers, behavioral studies of aquatic fauna usually track them through acoustic telemetry, but limited transmitter battery capacities restrict the length of time that the scientists can follow tagged animals. After determining the feasibility of using fish’s swimming motion to powder the transmitter, Huidong Li and his PNNL team replaced the battery with a flexible piezoelectric beam to channel energy from fish movement.
This innovation evolved from the Juvenile Salmon Acoustic Telemetry System (JSATS), which PNNL has been developing since 2001 to assess fish movement around dams and other constructions. Since that first iteration, the tool has become smaller, higher capacity and more energy efficient; however, the previous model required a tiny battery and lasted about 100 days. On the other hand, this relatively larger updated version, charged by a capacitator as the fish moves, could perform for decades. Funding for the self-powered tag came from the PNNL and the DOE’s Office of Energy Efficiency & Renewable Energy.
A lot of research has surrounded piezoelectricity over the last two decades because it offers high energy density and flexibility compared to other technologies. Past studies have used piezoelectric materials to channel mechanical energy from insects, larger animals like pigs, and humans. Prior piezoelectric models, consisting of stacks of piezoelectric ceramic elements needed to adequately convert power, have been bulky and heavy. Tags on fish, however, should be small and light to minimize related mortality and interference with behavior. This new transmitter features a thin, light piezoelectric material that reduces the burden of the tag on the animal.
Deng and colleagues first lab-tested the self-powered tag on a mechanical fish tail that they built based on a recording of fish swimming. Then they surgically implanted the device under the skin by the rear dorsal fins of two live fish, a white sturgeon and rainbow trout, and observed individual animals as they swam in circular tanks with underwater microphones. The system effectively picked up the tags’ beeping throughout the two-week experiment. The technology didn’t seem to interfere with the fishes’ movement. The researchers believe water temperature won’t significantly impact the transmitter’s performance because the piezoelectric and mechanical properties of the composite beam remain largely constant between 0 and 30 °C.
Next year, after further developing the transmitter for natural environments, PNNL will test the tag on juvenile white sturgeon along Washington’s Columbia and Snake rivers, where the device will have to overcome uncertainties posed by the challenges of catching fish, fish health and weather. The DOE’s Office of Technology Transitions and industry partners will fund this field research. If testing proves successful, the transmitter will become available to biologists and other researchers in 2017. The device could incorporate more composite beams or a rechargeable battery to harness greater power and operate even when the implanted fish isn’t moving enough.
Further studies could identify optimal design and placement of tags in different fish species for maximum energy production and minimal behavioral interference and investigate which sizes of fish can carry the device. Follow-up research could also look into the beam’s reliability and understand how it functions under high pressure. According to Deng, the technology could even be modified and tested on other animals with similar movement patterns.
“The ability to actively monitor fish over several years could entirely change the way that fish research is conducted,” concluded the researchers.
