VOA常速英语:New Technology Tracks Salmon in 3-D

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Salmon is important to the Pacific Northwest, both economically and culturally. But the fish's natural migratory behavior - traveling from inland rivers to the sea and back - has been interrupted in many places by dams.

Getting around those barriers is especially hard for juvenile salmon on their way to the Pacific Ocean. All that rushing water and noise makes them confused. While they swim back and forth, trying to get past the dam, they become easy targets for predators like birds and larger fish.
 
A delicate operation to tag a fish

Biologists are trying to solve that problem here at the fish tagging lab at John Day Dam, on Oregon's Columbia River. A dozen people scurry around with shallow containers holding young salmon. The fish don't flop out because they've been drugged.

James Hughes, with the Pacific Northwest National Lab, points to the one he's carrying and explains, "Once the fish loses equilibrium and is basically at the stage that this one is in, we take him from here to our data station and take all the metrics on him."
 
After some measurements, the tiny fish is quickly shuttled in the container to the operating table. Matt Wilberding is one of the scientists doing the intricate surgeries.

"I just try to take my time and do a careful surgery and put them back into the holding tank where they will stay for 24 hours and hopefully return to normal state."

He says it's important not to drink too much coffee so your hands remain steady.

A tiny incision, two stitches and the whole surgery takes about a minute.

Now, there are two transmitters inside the belly of this little 10-centimeter-long salmon. One of them is a long-lasting radio tag. It emits a signal whenever the fish swims near a special antenna along the river. The other puts out a coded ping, like an airplane's "black box." This sonic tag has a much longer range and provides much more detail about the fish's location.
 
But, as senior scientist Jeff McMichael notes, this tiny ping has to be detected over the roar of the dams. There is a lot of noise from the turbines, the thousands of popping bubbles, water cascading from the spillway and electrical generators.

So, he explains, "We chose a place in that noise environment where there wasn't very much noise."

It's a frequency that can blast through that underwater din.
 
3-D animations follow fish's movements

Now, a tagged fish can be heard by an underwater receiver as far as three football fields away. Researchers have placed hundreds of those receivers up and down the Columbia. Computers translate the tracking data they receive into an animation. That cartoon shows the movements of hundreds of tagged fish. Scientists already know that some go directly through the turbines. Others go over the spillway. Still others make their way down the waterslide built to help young fish around the dam. But the new sonic tags draw a more detailed image of what's happening with the tiny fish, showing exactly where they get mixed up or delayed on their downriver journey.
 
McMichael says most salmon make it around John Day just fine. But he wants to know why some don't, and eventually the data he's collecting could be used to modify the dam and change the facility's operations.

"All the easy questions have been answered," he says, "and it's the hard ones that remain. They're challenging, so when you are able to produce information that is necessary to make decisions, it's rewarding."

On a boat three kilometers upriver from the John Day Dam, the baby salmon are let go, five at a time. A scientist lowers a big bucket into the Columbia and the fish silently slip out and glide down into the greenish depths.
 
They still have the John Day Dam to contend with and 350 more kilometers of river to the Pacific Ocean. Along the way, thanks to their pinging bellies, scientists will be watching their every move.