Self-powering technology is showing up in a lot of places from clothing to tires, but fish seem to have been left out – until now. Scientists at the US Department of Energy's Pacific Northwest National Laboratory (PNNL) in Richland, Washington have developed a piezoelectric self-charging tracking tag that generates electricity from the fish's own movements, allowing researchers to keep tabs on them more accurately for longer periods of time.

Fish tags have come a long way in recent years. For decades, such tags were metal or plastic discs attached to a fish's body that depended on the help of conscientious fisherman to track their movements. Then along came tags that used miniature radio or audio transponders that could keep constant tabs on the comings and goings of fish.

Unfortunately, these radio tags had one severe limitation: the battery. Despite years of work on things like PNNL's Juvenile Salmon Acoustic Telemetry System, these tags were only good for about a hundred days. This might be good enough for tracking trout near hydroelectric dams, but it isn't much use with migratory eels that travel thousands of miles, or sturgeons that can live for up to 150 years.

To overcome these limitations, PNNL turned to a self-powering system that chief scientist Zhiqun "Daniel" Deng believes to be a first in fish tags. The PNNL tags consists of a flexible composite strip containing a length of piezoelectric material, a circuit board, and a beeping transducer. These piscine piezoelectrics come in two sizes. The first is 100 mm long and weighs 1.05 grams, and the other is 77 mm long and weighs 0.80 grams.

The tags are attached surgically to the dorsal fin of the fish to be tracked, and as it swims the strip generates power for the electronics. PNNL says that so long as the fish moves and is within range of underwater receivers, it can be tracked.

So far, Deng's team has tested the device on a robotic fish tail, a white sturgeon, and a rainbow trout. During tank tests, the fish emitted signals for two weeks without any hindrance to their swimming ability.

According to PNNL, the new tags will undergo lab testing for the next year followed by tagging of sturgeon in the Columbia and Snake rivers in Washington state. If successful, the technology will be adapted for different species with special emphasis on deeper diving varieties.

"Our self-powered acoustic tag can help us better understand how dams and ocean energy devices affect fish behavior," says Deng. "Sturgeon are ancient fish and have been on this planet for millions of years. This tag can help us mitigate the impacts of human activities, and help these fish survive many more years."

The research was published in Scientific Reports.

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