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New acoustic camera captures picture of fish passage

Scientists at the University of Washington's Applied Physics Laboratory in Seattle developed a camera that can capture high resolution images through murky water



An acoustic camera originally developed for the Navy now may provide a new method of viewing fish behavior at structures on hydropower dams. This image captured by the camera shows fish moving near a structure at The Dalles Dam on the Columbia River between Washington and Oregon. Using the acoustic camera, PNNL fisheries biologists in June tracked the movement of juvenile salmon as they approached a sluiceway entrance at the dam.

August 13—If a picture is worth a thousand words, then how valuable is a high-resolution image of fish seen through murky water? Very valuable, according to scientists seeking to understand fish movement near hydropower dams. Recently, fisheries biologists at Pacific Northwest National Laboratory deployed an acoustic camera originally designed for the Navy at a dam in the Northwest to study and illuminate their understanding of fish behavior.

In its first fisheries application, the camera provided researchers at PNNL with some of the best images yet taken of juvenile salmon movement near a dam. The images showed an individual fish's undulating movements, and its head and tail were visible, even at distances of 30 feet. Evaluations were done at the U.S. Army Corps of Engineers' The Dalles Dam, a 2,089-foot-wide structure straddling the Columbia River between Washington and Oregon.

Scientists at the University of Washington's Applied Physics Laboratory in Seattle initially developed the camera for the Navy's Space and Naval Warfare Systems Center. The Corps' biologists agreed with the value of such detailed images, purchased the UW's latest version and funded PNNL to assess the system's effectiveness in evaluating fish bypass measures. PNNL and the Corps worked together to develop the camera's use for fisheries-related work and the first application currently under way at the dam.

"We recognized the potential of this instrument and are stretching the limits of what it was designed for," says Russ Moursund, Environmental Technology Division and PNNL project leader. "We are the first to apply the acoustic camera to fisheries issues. So far, it has captured images with greater detail and at greater distances than any other methods we've used. We'll continue to conduct tests to further evaluate its effectiveness in studying fish behavior."

Other techniques have greater limitations than the acoustic camera. Traditional sonar techniques have sufficient range for fish studies but can't determine the size or shape of fish. Optical systems, such as video cameras, provide clear pictures of fish yet are hampered by low light or turbid water, seldom capturing images more than 3 feet away. The acoustic camera, however, can capture near-video-quality grayscale images from up to 30 feet away, regardless of visibility, and without the use of electronic tracking tags. Images also can be taken of fish located in confined spaces and near bubbles, which can deflect traditional sonar methods and interfere with data collection.

The UW began developing the technology in the mid-1990s for Navy divers to use in underwater surveillance to detect limpet mines attached to hulls of ships. In 1999, Moursund recognized the potential application for fisheries issues and, with the system's designer, Ed Belcher, tested the acoustic camera at PNNL's aquatic research center in Richland.

Earlier this spring, researchers at PNNL used it to study the fish bypass system of J-occlusion plates at The Dalles Dam, operated by the Corps' Portland District. The Corps installed J-occlusion plates, which are so named because of their similarity in shape to the letter J, in front of seven turbine units to help guide fish away from turbines. Using the acoustic camera, PNNL researchers collected data on fish activity in these areas when the plates were and weren't present. The Corps will consider this and other information to determine whether significant numbers of smolts are lost to gaps between adjacent plates.

This fall, PNNL fisheries biologists expect to deploy the camera at The Dalles and Bonneville dams. Additional tests will help quantify how well the acoustic camera can provide fish size and shape estimates.

"With this system, we'll be able to observe how juvenile fish respond to structures added to dams, such as trash racks or turbine intake screens," says Gene Ploskey, ETD and PNNL project co-lead. "We also could study adult fish responses to conditions in fish ladders. Each of these studies would help expand our understanding of how fish are reacting to these structures and provide new information that could be used to mitigate the impact of dam operations on fish survival."

The camera system, called the Dual-Frequency Identification Sonar or DIDSON, uses an acoustic lens and can operate on two frequencies. By using up to 96 different sonar beams, the system flushes out more background noise and allows better image processing.—by Staci Maloof

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