Tuesday, July 13, 2010

Scientists Will Track Fish With Underwater Gliders

By Margaret Bauman

Researchers at the University of Alaska Fairbanks say they have successfully tested a form of underwater glider for use in tracking tagged fish. Now they are planning to use the gliders to gather oceanographic information in the Chukchi Sea, UAF officials said in a statement issued in early June.

The autonomous underwater vehicles were tested in May by Peter Winsor, an associate professor of physical oceanography, and Andrew Seitz, an assistant professor of fisheries.

Winsor and Seitz suspended acoustic tags, usually implanted in fish, at different depths along a buoy line near Juneau. They then deployed two gliders fitted with an acoustic listening device to “hear” the signals from the tags. These are the first gliders to be deployed in Alaska with an acoustic monitoring device to track tagged fish, they said.

Each glider is about five feet long and flies like an airplane through the water in an up-and-down motion. They are propelled using an internal bladder that works much like a fish’s swim bladder. When the bladder expands, the glider moves toward the surface. When it contracts, it moves toward the seafloor, converting changes in water depth into forward movement.

The gliders move at a speed of nearly one mile per hour, can operate for up to three months, and cover thousands of miles of ocean, Winsor said. At the surface, the glider transmits data, including its location and oceanographic readings, directly to scientists.

Using the gliders, the researchers can learn where the fish go, and measure the physical, chemical and biological environment of the ocean at the same time,” said Winsor.

Traditional methods of tracking tagged fish include using a ship equipped with an acoustic listening device, or by using what scientists call a “listening line,” which is a series of hydrophones attached to the seafloor.

“The problem with using hydrophones is that they stay in one place and the tagged fish have to move near enough to the hydrophones to be detected,” said Seitz. “This can create big geographic gaps in your data, especially in the vast oceans surrounding Alaska.”

The gliders can be programmed to follow tagged fish, Seitz and Winsor said. The technology is ideal for Alaska waters because the gliders can cover large distances and are much less expensive than using a ship or sets of hydrophones.

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