Batteries not included: Swimming charges innovative fish tags from PNNL

Swimming fish could soon power their own tracking tags with technology developed by scientists at the Pacific Northwest National Laboratory in Richland.

The tags combine a tiny transmitter that beeps regularly with a strip of what’s known as piezoelectric material designed to generate electricity from the motion of a swishing tail, according to a study published this week.

The entire system is less than 4 inches long and weighs about as much as a paper clip.

“We wanted it to be powerful enough to generate enough power, but it also needs to be small so you can study smaller fish,” said lead scientist Zhiqun “Daniel” Deng, who said this self-powered tag builds on years of work to make the transmitters smaller and more efficient.

Deng credits a diverse team of scientists — electronics engineers developing the beeping transmitter, materials scientists who understand how physical movement can create electricity in certain ceramic and crystalline materials, and fish biologists — with the breakthrough to this self-powered system.

Tracking tags are crucial for scientists studying where and when fish feed, spawn and get delayed by dams. But batteries are either heavy or short-lived, which creates challenges for tagging small, juvenile fish.

Many salmon in the region are tagged with rice-sized passive tags that provide an identification code to a nearby detection device, often used in fish ladders and hatcheries. But these common tags can’t be used for tracking studies that want to measure movement in real time. Those studies have usually been done with battery-powered tags that beep location signals for a few weeks or months.

Deng’s lab had developed transmitters that can beep for about 100 days, but this one will work for as long as the fish keeps swimming.

If the fish stop and rest, though, the tags stop sending out signals. Deng said his lab is also developing a version with a rechargeable battery to address that potential problem.

“With (a) rechargeable battery, they can recharge when they swim, but you can control the transmission more regularly,” Deng said. “But if they don’t swim, you still know where they are, so this version is still very useful.”

The prototype was tested first on a robotic fish tail, then on juvenile sturgeon and rainbow trout in the lab, Deng said. Field trials on sturgeon are planned for next summer.

There’s lots of optimization work ahead for the technology to be used by fish biologists, Deng said, including fine-tuning it to individual species and figuring out what it would cost if produced commercially.

Deng said he expects his lab to continue improving and shrinking the technology so it can be used on even smaller fish in the future.

“Our goal to make a tag as small as possible and our other goal is to make the tags last as long as possible,” he said. “For us to use this for other fish, definitely a lot more research needs to be done.”

This story was originally published October 1, 2016 at 4:54 PM with the headline "Batteries not included: Swimming charges innovative fish tags from PNNL."