Oregon spotted frog habitat is improving in some areas and seasons while degrading in others under a legal settlement in the Deschutes Basin.
Published October 4, 2017
A legal settlement intended to upgrade conditions for the Oregon spotted frog is having uneven impacts on the threatened species’ habitat, according to federal biologists.
The agreement was struck last year to resolve a lawsuit between environmental groups, irrigation districts and the federal government over the operation of several dams in the region.
While conditions for the spotted frog improved in portions of the basin during certain seasons, they were degraded in other locations and times under the deal, according to a recent “biological opinion” from the U.S. Fish and Wildlife Service.
“We call this the push-down, pop-up system,” said Bridget Moran, field supervisor of the agency’s office in Bend, Ore.
In other words, when problems are suppressed in some areas they are aggravated in others due to the complexity of the irrigation system, which relies on water from the Crane Prairie, Wickiup and Crescent Lake reservoirs.
Under the settlement, the amount of water is reduced for growers in five irrigation districts to make more available to the frog, which is protected under the Endangered Species Act.
As reservoirs are drawn down, the water level falls below vegetation that spotted frogs rely upon for breeding and shelter from predators, said Moran.
“It’s really about whether the level of flow allows the frogs to access their habitat,” she said.
However, retaining water in one part of the system means that it’s reduced somewhere else, she said. For example, filling a reservoir requires reducing downstream river flows.
Nonetheless, the Fish and Wildlife Service concluded in its biological opinion that the water regime mandated by the settlement won’t jeopardize the frog’s continued existence or destroy its habitat.
“On the balance, there is slight improvement, most notably at the Crane Prairie reservoir,” which is important because it contains a healthy population of frogs, Moran said.
Moran characterized the legal settlement as the “bridge” to a more comprehensive “habitat conservation plan,” or HCP, for the spotted frog that’s due in 2019. At that point, the current deal is expected to expire.
“It will be many different features but they all build around increasing winter flows over time,” which provides frogs with the opportunity to reach overwinter habitat, she said.
Increased flows will be supplemented with habitat restoration work aimed at returning the system’s rivers to a more natural state.
Over the 70 years of reservoir operations, heavy water flows released from reservoirs during summer have “scarred” river beds, making channels deeper, said Moran. As a result, water doesn’t reach adjacent wetland vegetation, cutting off spotted frogs from habitat.
Meanwhile, what vegetation does grow along river banks is flooded, she said. “It comes up so high, everything gets inundated.”
Habitat restoration work aims to reconnect the river flows with nearby habitat. The HCP will also include control of bull frogs, which predate on spotted frogs and compete for habitat, and treatment of reed canary grass, an invasive species.
Due to a healthy snowpack last winter, the settlement wasn’t seriously damaging to irrigators in 2017, said Ken Rieck, general manager of the Tumalo Irrigation District, a defendant in the case.
On average, the district stands to lose about half the stored water that would usually be available for irrigation due to the agreement, he said. This year, it only lost about 20 percent, but in a “bad year,” the loss could reach 80 percent.
“We really didn’t get the full effect we could have,” Rieck said.
Under the settlement, water that would normally be stored in Crescent Lake for the district’s irrigation system is being redirected into winter stream flows for the spotted frog.
Traditionally, the district lost roughly half of available irrigation water to seepage in unlined canals, Rieck said. Now, it’s installing piping to stop the leakage, allowing more water to be devoted to frog habitat without reducing irrigation supplies as sharply.
“The more pipe we put in the ground, the more of that water we’ll be able to recover,” he said. “Our goal is to be as close to 100 percent efficient in our delivery system as possible and that will be our defense.”