Every year since 2015, the Eel River Recovery Project (ERRP) has joined Dr. Sarah Kupferberg to help count yellow-legged frog eggs on the South Fork Eel River at Benbow. Another count will take place on Saturday, May 18 at 10 AM with participants meeting at the entrance to Benbow State Park. This year’s count will indicate whether the frog egg rescue in 2016 to avoid impacts from Benbow Dam were successful.
Egg masses are laid in quiet water near the stream margin where it is too shallow for fish to forage. The eggs look like a golf ball sized mass of caviar when newly laid and then the mass expands to about the size of a tennis ball just before hatching and is more tan colored as the mass gets covered in flocculent material. Yellow legged frogs in various life-history phases are important food for avian predators and garter snakes.
Dr. Sarah Kupferberg is one of the foremost authorities on yellow-legged frogs in California. She has collected more than 25 years of data on upper South Fork Eel River populations on the University of California Angelo Reserve. “It is great to do surveys in the Eel River because there is an abundance of yellow-legged frogs, but the species is showing declining trends in other parts of the State and are extinct in 2/3 of their former range” said Sarah. She counts frogs in the egg stage because enumerating tadpoles or finding adults to count would be much more difficult. Sarah has developed an index of egg masses per kilometer to track populations.
Sarah’s long term upper South Fork database has shown a range of 80-175 egg masses per mile, with the highest count coming in 2016 and lowest during the prolonged drought of 2013-2015. Filling of Benbow Lake ceased in 2008 due to concerns about endangered salmon and steelhead, but it took a while for frog numbers to increase as the former lake reverted to river habitat. Yellow-legged frog egg counts by Sarah from 2012-2015 indicated only 35-75 clusters per kilometer, but that number increased to 269 in 2016 and remained high in 2017 and 2018 with scores of 188 and 210, respectively.
In 2016, ERRP volunteers assisted Dr. Kupferberg with relocating yellow-legged frog egg masses that would be harmed by the removal of Benbow Dam. Kayaks and large plastic tubs were used to move eggs and the rocks to which they were attached to adjacent reaches away from demolition activity. Sarah chose the location for where eggs were placed making sure that depth and cover were similar to the species natural preferences. The 2019 count will be an indicator of the success of the 2016 egg mass relocation as females mature at three years of age.
I you’d like to assist in this year’s survey, meet Sarah near the entrance of Benbow State Park at 10 AM on Saturday, May 18. Wear river shoes and be prepared to wade the edge of the stream. Polarized sunglasses are ideal for cutting glare when counting frog eggs. Call Walker Wise at (707) 502-8170 for more information or see www.eelriverrecovery.org and ERRP Facebook.