Under the Ice: Studying Yosemite's Frogs in WinterLatest update July 21, 2019 Started on October 29, 2018
The objective of this expedition is to use a small remotely-operated vehicle (OpenROV Trident) to explore the underwater world of the endangered mountain yellow-legged frog during winter, when frogs are in lakes and beneath several meters of snow and ice. To describe frog distribution and habitat use, we will conduct several under-ice deployments in lakes in Yosemite National Park that contain large mountain yellow-legged frog populations. The resulting information will provide important insights to guide ongoing frog recovery efforts.
We've made several under-ice dives during the past year and have learned some amazing things about mountain yellow-legged frogs. During winter, adult frogs are rare in the habitats accessible to the Trident ROV, suggesting that most may spend the winter in deep crevices under the lake banks. In contrast to the scarcity of adult frogs, we have encountered large groups of tadpoles on every dive, and observations made have raised numerous additional questions. How are they able to remain active at temperatures near 0 degrees C? Why do they aggregate in large groups? Due to the thick ice on the surface of the lake, the under-ice environment is characterized by complete darkness. How do tadpoles find each other in the dark?
Our study lake is still ice-covered, and likely will remain so until mid-July. The ice is substantially thinner now than it was during mid-winter, and that allows more light to penetrate into the under-ice environment. We want to take advantage of that increased visibility, and our next deployment will take place shortly. We'll be accompanied by David Lang from OpenROV, and we're all looking forward to it.
To gain experience piloting the Trident, today we deployed a borrowed unit in a roadside lake. It took awhile to gain the eye-thumb coordination necessary to maneuver the Trident, and it will be a few more deployments before I feel proficient enough to pilot it in a lake with mountain yellow-legged frogs. Our deployment ended when we sucked some abandoned monofilament fishing line into two of the motors. We hadn't thought to bring the necessary tools with us to remove the line in the field (knife, screwdriver, allen wrench) but were able to remove it back at the laboratory. That was a good reminder of what me might need during our future deployments in our more remote study lakes.
We are a group of scientists who study lakes in California's Sierra Nevada mountains. One of the native inhabitants of those lakes is the mountain yellow-legged frog, once the most common amphibian in the Sierra Nevada but now listed as "endangered" under the U.S. Endangered Species Act due to dramatic declines during the past century. A decades-long effort to prevent the extinction of this frog has made it one of the best-studied frogs on Earth, but this is based almost entirely on observations made during the summer active season. During winter, frogs are deep underwater and beneath several meters of snow and ice, making observations difficult at best. However, the recent availability of small underwater drones has made exploration of these habitats possible. To describe frog distribution and habitat use during winter, we'll conduct several deployments of an ROV (OpenROV Trident) under the ice in lakes in Yosemite National Park.
To prepare, with the assistance of several OpenROV engineers, during the 2017-2018 winter we tested a Trident and were amazed at its capabilities under these challenging conditions. We've also created high resolution bathymetric maps of the study lakes to guide our deployments. The lakes will be freezing over soon and we are anxious to start our exploration!
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