The tagging of fish and other wildlife is one of the core tools that scientists use to get a picture of how an animal population is faring. Tags can show patterns in movement over time and how wildlife react to different obstacles or threats in their environment.
Until now, fish tags have had a limited lifetime because they've relied on batteries for power. Scientists can only see a snapshot of a fish's movements that ends when the battery dies, but researchers at Pacific Northwest National Laboratory (PNNL) have created a new fish tag that is powered by the fish's movements meaning the tag will track the fish as long as it keeps swimming.
This new tag could be a major breakthrough for fish studies. A self-powered tag can detect the movements of long-living fish like sturgeon and capture the migration cycles of fish like eel and lamprey for their entire lives. It will also show how man-made structures and technology impact their lives.
"Our self-powered acoustic tag can help us better understand how dams and ocean energy devices affect fish behavior," said PNNL chief scientist Zhiqun "Daniel" 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 team has been working on extending the life of fish tags for well over a decade. They've scaled them down and improved energy efficiency, but still only hit a tag life of 100 days. The new tag utilizes a tiny piezoelectric generator to keep the instrument charged as long as the fish is moving, which is to say its whole life.
The tag is composed of three parts: a piezoelectric strip, a circuit board and a beeping transducer, the sounds of which are recorded by underwater receivers for tracking the fish. There are two sizes of tag, 77 mm and 100 mm, for smaller and larger fish and they weigh about the same as a paper clip.
The tag was tested using a robotic fish tail to ensure that it kept its charge through typical fish movement and then the two sizes were tried on a rainbow trout and a sturgeon. The tags were inserted near the dorsal fins of the fish and they were kept in a tank outfitted with an underwater receiver for two weeks to test the tag performance. The tags worked perfectly without affecting the fish's swimming.
The tags will be used in a field study of sturgeon in the Columbia and Snake rivers of Washington next year. The researchers also want to continue testing the tag to find the best placement and size of tag for more species of fish and whether it can handle high pressure environments. If so, the tag could potentially be used to study sharks and other ocean fish.