Until now, no one has been able to track what happens to salmon during their final migration to sea once they pass Bonneville dam, 240km upriver.
The federal government spends more than US$700 million a year on the Columbia river basin to sustain and rebuild salmon runs. The spending, however, has not turned things around for many stocks, particularly those bound to the farthest upriver reaches of the Snake river, past eight large hydro power projects.
The US Army Corps of Engineers, which runs the Columbia's extensive system of hydroelectric dams, spent close to US$2 million to develop the new tracking system.
To track the fish, biologists suspended two rows of automated electronic sensors, called hydrophones, to listen for baby salmon passing by. The sensors float below the surface of the river tethered to a heavy steel anchor. The sensors pick up recorded pinging signals sent from transmitters implanted in a thousand smolts.
National Marine Fisheries Service biologists say the tracking system will enable them to quantify salmon mortality due to travel through the hydro power system, as well as improve the system to reduce the causes of this mortality.
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