High-tech machine helping salmon survive

May 15, 2009 6:55:28 PM PDT
State water officials have come up with a creative way to save the shrinking Chinook salmon population. They showed off something called a bubble curtain at a critical juncture along the San Joaquin River.

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A high-tech bubble machine is proving to be a life-saver for young Chinook salmon migrating from the San Joaquin River to the San Francisco Bay.

Chinook numbers have rapidly declined in recent years.

The 112-meter bubble curtain combines bright strobe lights, loud noises and bubbles to create an underwater wall that diverts the fish toward the main stem of the San Joaquin River, the safest route to the bay.

"We literally have high intensity speakers under water that utilize sound and the bubbles absorb that sound and that creates a deterrent for the fish to deflect them away from a particular destination," said Trent Gathright from EIMCO Water Technologies.

Using an underwater sonar and tagged hatchery Chinook, scientists found the barrier to be highly effective.

"Seventy-nine percent of the fish that come down the San Joaquin stay in the San Joaquin when the barrier is on," said biologist Mark Bowen.

Without any deterrent, about half would head down a channel called old river, which leads straight to the giant pumps near Tracy.

In past years, the Department of Water Resources would just install a rock wall here to keep the Chinook salmon on the main stem of the San Joaquin River.

The rock deterred the Chinook, but proved detrimental to other species, like threatened Delta smelt.

The bubble barrier seems to work well for both species.

"It not only protects salmon, which is really what we're trying to do here, but it also provides the flows to move through, which helps protect Delta smelt," said Jerry Johns from the California Department of Water Resources.

Scientists plan to insert and remove the bubble mechanism each spring to ensure the Chinook have a safe passage to the sea.

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