Sonar is helping the Lower Elwha Klallam Tribe get an accurate estimate of some species of salmon returning to the Elwha River.
The Tribe has been counting the number of returning adult chinook salmon and steelhead using a sonar camera since 2008 with positive results.
The camera is placed just below the water’s surface, sending out sound beams that “hit” a fish and reflect back to the camera. The camera is connected to a computer that translates the sound beams into pixels that are counted as fish.
This is part of the overall effort to see how many fish return to the river following the recent removal of the Elwha and Glines Canyon dams. The Elwha was removed completely by March 2013 and the Glines Canyon is expected to be fully removed by end of 2014.
“Elwha dam has only been out for two years and Glines Canyon dam hasn’t been completely removed, so these fish are in the early stages of responding to dam removal,” said Keith Denton, a tribal consultant overseeing the sonar program. “We’re trying to count how many steelhead and chinook are coming back over time.”
Chinook are easy to count because the bulk of the run enters the river over a three week period in the summer and the only issues are snowmelt and a decreasing river level, Denton said. The steelhead run is harder to manage, as the run goes for six months, from January through June, during which the river flow and levels fluctuate.
“You can get real time data this way as an alternative to surveying the river for nests,” Denton said. “Traditional visual surveys of nests or redds have been difficult during dam removal because of the increased sediment in the water, making seeing them difficult.”
Sonar is commonly used in British Columbia, Canada and Alaska as a population assessment tool.
“The Elwha is different than other places where this type of work is taking place though because we have relatively small salmon and steelhead runs compared to rivers in Alaska and British Columbia and because of the constantly changing river conditions during dam removal,” Denton said.