science news
Keeping Tabs on Millions of Salmon
In the Pacific Northwest, salmon migrating from fresh waters in the Columbia River Basin to the Pacific might as well be on a leash. Tucked away inside millions of salmon are tiny transponders -- each approximately the size of a grain of rice -- that allow scientists to track the salmon's movements throughout its life. Initially developed by Destron Fearing in the 1980's, Passive Integrated Transponder (PIT) technology is essentially the same as that used to electronically tag livestock, however the process of tagging fish is a bit more slippery. As many as 100,000 fish a day may receive a PIT tag, Tags are programmed with one of 275 billion unique code numbers and placed into the fish's body cavity. Once tagged, the fish are released into the wild to begin their migration to the waters of the Pacific Ocean. Along the way, the fish are tracked as they travel through more than 400 detection sites, the last of which is the Bonneville Lock and Dam just outside of Portland, Oregon. Here the world's largest radio frequency identification (RFID) antenna, which measures an imposing 17 feet tall by 17 feet wide, reads the identification numbers of tagged fish as they swim past at more than 35 mph. This information is then relayed to a computerized database where it is used to identify and track the fish one final time before they swim out to sea. How fast does this process happen? In less than 1/30 of a second -- literally the blink of an eye. When the mature salmon return to spawn five years later and once again pass through the detection sites, researchers are able to collect unprecedented variables of data that help scientists track the health of the salmon population and the world's oceans. And it all starts with a microchip the size of a grain of rice.
As many as 100,000 fish a day may receive a PIT tag. Tags -- the size of a grain of rice -- are programmed with one of 275 billion unique code numbers and placed into the fish's body cavity.
Sound Advice Need to know the speed of sound in water for a given temperature, salinity and/or depth? Several interactive calculators are available on-line from the UK's National Physical Laboratory at http://www.npl.co.uk/ acoustics/techguides/ soundseawater/index. html (Source: Brock Rosenthal) 16 MTR October 2007
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