Recoverable sensors solve the mystery of what kills fish travelling through man-made river obstacles. By David Ferris
Every spring in the Pacific Northwest, tens of millions of smolt (young salmon) swim through the Columbia River’s hydroelectric dams on their way to the ocean, and every year as many as 10 per cent emerge wounded or dead. The exact cause of the damage was a long-standing mystery.
So Tom Carlson, a senior scientist at Pacific Northwest National Laboratory, invented a device that could pass through the dams while recording data: the Sensor Fish. After hundreds of tests, Carlson has the answer. As a salmon wriggles through the turbine blades, it suffers an abrupt drop in pressure. Its swim bladder suddenly expands or bursts, damaging other internal organs. The pressure change can also create air bubbles in the fish’s blood, causing a piscine version of divers’ bends.
While Carlson covered the Sensor Fish in a polycarbonate plastic shell, Paul Heisey, a fisheries scientist with Normandeau Associates, attached the device’s sensors to live fish for a more complete picture.
“The condition of the recaptured fish, along with the hydraulic conditions obtained by the Sensor Fish, provide information on the type, severity and cause of injuries,” Heisey says. Using that data, he plans to propose modifications to power stations and spillways to make passage through them more benign for fish.
Carlson’s team, meanwhile, is adapting the sensor – that is, shrinking it to a 2,5 cm sphere – to create surrogates for many types of fish encountering various infrastructures.
What it is
Scientists developed the Sensor Fish to collect forensic data on what kills fish when they pass through dams and other aquatic infrastructure.
The device has accelerometers that detect impacts, a water-pressure gauge, and gyroscopes to measure the spin of fish caught in turbine wash.
How data is recovered
Time-delay balloons inflate, bringing the sensor bobbing to the surface. Researchers recover the device and download the information.