Fisheries biologists at the US Department of Energy’s Pacific Northwest National Laboratories are employing an acoustic camera originally designed for US navy to study the behaviour of fish around dams.
Scientists at the University of Washington’s (UW) Applied Physics Laboratory initially developed the camera, called the Dual-Frequency Identification Sonar or DIDSON, for the US Navy’s Space and Naval Warfare Systems Centre.
The camera system 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.
In its first fisheries application, the camera provided PNNL researchers with some of the best images yet taken of juvenile salmon movement near a dam.
The images showed an individual fish’s undulating movements at distances of up to 30 feet and evaluations were done at the US Army Corps of Engineers’ Dalles Dam.
The Corps’ biologists were so impressed with the images they purchased the UW’s latest version and funded PNNL to assess the system’s effectiveness in evaluating fish bypass measures.
‘We are the first to apply the acoustic camera to fisheries issues,’ said Russ Moursund, PNNL project leader. ‘So far, it has captured images with greater detail and at greater distances than any other methods we’ve used.’
In 1999, Moursund recognised the potential application for fisheries issues and, with the system’s designer, Ed Belcher, tested the acoustic camera at PNNL’s aquatic research centre.
Other techniques such as sonar and optical systems are said to have greater limitations than the acoustic camera.
The acoustic camera is said to be able to capture near-video-quality greyscale images from up to 30 feet away, regardless of visibility, and without the use of electronic tracking tags.
Images can also be taken of fish located in confined spaces and near bubbles, which can deflect traditional sonar methods and interfere with data collection.
Earlier this year, PNNL researchers used it to study the fish bypass system of J-occlusion plates at the Dalles Dam.
The Corps installed J-occlusion plates 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.
Additional tests will help quantify how well the acoustic camera can provide fish size and shape estimates.