MSU researchers seek the shadow of a fish

By JEAN ARTHUR MSU News Service

Montana State University professor Joe Shaw redefined the term "fly fishing" when he and a student researcher flew over Yellowstone Lake this fall looking for fish shadows.

Shaw had taken laser radar -- or lidar -- technology, which resembles a telescope, and bolted it on an airplane. The plane was flown over the lake while he and graduate student Nathan Seldomridge beamed laser rays into the water.

They hoped to locate groups of spawning, non-native lake trout that threaten the native cutthroat trout population.

The study's results could help Yellowstone National Park fisheries biologists with a plan to eradicate the piscivorous predator from the pristine headwaters of the Yellowstone River.

"We send a lidar pulse down -- it looks like a green beam of light -- and it scatters off the objects suspended in the water," said Shaw, an electrical and computer engineering professor. "We record the depth of the objects and images of shadows of the objects using an electronic camera."

Lake trout are invasive species and an effective predator to Yellowstone cutthroat trout. After they were found in the lake in 1994, park fisheries biologists launched an aggressive lake-trout control effort.

The park's "no-harvest limits" on the fish removed thousands of them from Yellowstone Lake. Catch-and-release-only fishing rules have applied to most of the park's native fish since the early 1970s.

This fall, Shaw and Seldomridge flew 500 feet above the lake's West Thumb area, where fisheries biologists had indicated they would find schools of spawning fish, said Seldomridge, a graduate student in electrical engineering from Colorado.

Lake trout usually spend their days 30 meters deep where lidar cannot penetrate because of murky water, he said. But during September's spawning season, the fish swim in about 10 meters of water.

"We can't be sure that we saw any lake trout until the data analysis is complete this spring," said Seldomridge. "But lidar has been proven to see silhouettes of fish. So from relative size, we can tell if what we see is lake trout, which are generally three to four times the size of cutthroat."

Adult lake trout reach four to 25 pounds while Yellowstone cutthroat mature to about one-and-a-half pounds.

After logging seven hours of data, the task remains to read the shadows cast from fish in the lidar beam and recorded on video.

Rianon Tiensvold, a junior in electrical and computer engineering from Frenchtown who works in Shaw's Optical Remote Sensor Lab on the MSU campus, is examining each video frame for fish shadows.

"I use existing software to process the depth profiles, but I will also investigate alternate processing methods for identifying lake trout and cutthroat trout in the laser images," she said. "We are hoping these image-processing tools will enable the fisheries biologists to be able to distinguish between the lake trout and cutthroat trout species."

She expects to complete the analysis by May.

"The project offered a lot of challenges for the technology and took a couple of years to organize," said Shaw. "In the end, we hope to demonstrate the utility of this technique and develop even smaller systems that could be flown often on small airplanes to help monitor the Yellowstone Lake environment."

The project is funded through a $45,000 Montana Space Grant Consortium grant and was a collaborative effort with the National Oceanic and Atmospheric Administration. Results are expected in May.

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