The Mazama newt in Crater Lake is fighting for its survival from a predatory crayfish introduced in 1915

The Crater Lake newt, also known as the Mazama newt, is facing a challenge for survival due to predation from the signal crayfish. The U.S. Fish and Wildlife Service is now reviewing the situation and considering as it considers listing the newt as endangered.

Park managers put the signal crayfish into the lake in 1915 as a food source for the previously introduced non-native rainbow trout and kokanee – a landlocked salmon. The Mazama Newt is a distinct dark-colored subspecies of the rough-skinned newt and is found only in Crater Lake National Park.

Listing the newt involves an initial evaluation process called a 90-day finding, followed by a full status review, which could take a year and a half. The Klamath Tribes News contacted Cat Darst, the Nevada and California Classification Coordinator for the U.S. Fish and Wildlife Service. She said the newt is not yet listed as endangered but is under consideration due to a petition from the Center for Biological Diversity. The petition suggests that the newt may be threatened by non-native signal crayfish, which were introduced to the lake in 1915 as a food source for non-native fish. The petition stated that the newt’s restricted range and predation pressure from crayfish are significant concerns.

A complete, in-depth evaluation process will follow the 90-day finding. This includes a comprehensive review of the species’ history and threats and a biological risk assessment to determine if listing under the Endangered Species Act is warranted due to potential threats, particularly predation by non-native signal crayfish.

The Center for Biological Diversity is based in Tucson, Arizona, with offices nationwide. Darst said it files many petitions for listing species under the Endangered Species Act and that the species would be prioritized based on the national listing work plan, which could take a few years.

“We got the petition in November of 2023, and the first thing we do at the U.S. Fish and Wildlife Service when we receive a petition, which is a request from the public for us to evaluate a CC, is we just do a cursory evaluation of what’s in the petition, and that’s called a 90-day finding,” Darst explained. “And all we’ve done so far is a 90-day finding on the petition that we received last November, and we found that, yes, the petition suggests that we should do a further in-depth status review to see if the species should go on the list.”

The full in-depth evaluation, she explained, is when the U.S. Forest Service looks at all of the factors that could be influencing the species, including the entire history of the species, threats, and how they may be projected into the future to do a species status assessment, which is a biological risk assessment of the species. “And that usually takes us about a year-and-a-half,” she said, “and it’s that we take into our decision-makers, and they overlay policy definitions on that scientific document to determine whether or not the species warrants listing under the Endangered Species Act.”

As for the likelihood of the Mazama newt being listed, Darst said that the petition presents credible information that predation by non-native signal crayfish that have been introduced to the Crater Lake may be a problem for the species and was substantial, and that’s what was found when they did the 90-day finding. “That seems to be the biggest threat to the species,” she said. “But we found that there may be other threats that need further evaluation, which we would do in our CC status assessment, and that’s things like evaluating habitat and food web alteration by the signal crayfish; effects of climate change; effects of reduced population size from predation by the signal crayfish, and then the range restriction.”

David Herring is an aquatic ecologist at Crater Lake National Park. He also spoke to the Klamath Tribes News in a phone interview. He said that the Mazama newts were once found where crayfish were absent, but now crayfish occupy nearly the entire lakeshore. Herring’s team studies newt and crayfish interactions, noting crayfish’s impact on newt behavior and habitat. Despite efforts to remove crayfish, their deep, extensive distribution in the lake makes eradication challenging, Herring said. “The park is exploring captivity for newts and genetic manipulation for crayfish control while maintaining hope for conservation,” he said.

He stated that the newt’s restricted range and intense predation pressure from non-native crayfish could limit their habitat if the crayfish dominate the lake. As for the estimated population of the newt, he said this would be evaluated during a full-scale status assessment. Herring expressed disbelief at the historical management decisions that led to introducing non-native species to the lake.

“I actually spent some time over a decade ago now, combing through scrapbooks that the park had of newspaper clippings from the park’s history,” Herring said, “and we found some headlines from 1915 that said that signal crayfish were being intentionally introduced by the Park Service to provide food for the introduced trout that are in the lake. So, first, people came and put trout in the lake, which did not naturally exist there, and then had a great idea, later, or not so great idea, to introduce the second species, these crayfish, so that the trout would have more to eat.”

During the park’s history, he said several other species of salmon and trout were introduced, but the rainbow and kokanee persisted and naturally reproduced in the lake. Crater Lake was naturally fishless before the non-native fish were introduced. One note about fishing in the lake: a fishing license is not required, and there is no daily limit on the amount of fish you can catch.

The newt’s struggle for survival against the crayfish is a heavyweight against the lightweight in this battle. “It seems like that’s the case,” Herring said. “We did some experiments several years ago in the lake to try to describe this interaction or to understand it more. And in those experiments, we actually put both crayfish and newts together in simulated habitats called mesocosms. They were basically big cattle troughs, and we found that when the crayfish were present in those enclosures with newts, the newts’ behavior totally changed, and they weren’t able to find suitable resting places under rocks and things like that because the crayfish just displaced them from those areas.”

The Mazama newt’s diet consists of smaller prey, such as snails and aquatic insects that live on the lake bottom, and the crayfish has also impacted these important food sources of the newt. “In places where we’ve studied this, we’ve studied places where we have crayfish in the lake and places where we still don’t have crayfish, and we’ve found that there’s a dramatic reduction in the abundance of those aquatic insects in places where the crayfish are, and that’s because the crayfish eat those things,” Herring explained.

As for a solution to eradicating the crayfish, Herring said it’s an ongoing challenge and not easily solved. He said they are found as deep as 600 feet below the lake surface, and due to their extensive distribution in the lake in extensively rocky substrate, eliminating them is a daunting task. “Extensive distribution, the really rocky substrate in the lake, which gives the greater slots places to hide, and just the sheer size of greater Lake, eradicating them now, using current methods doesn’t appear to be feasible, but we’re still working on exploring approaches to figure out how we might be able to do that in the future,” he said.   

As work continues on a possible solution to eradicating the signal crayfish from Crater Lake, Herring said conservation efforts are underway to protect future generations. “As we try to figure out how we can address the crayfish problem, we’re at the same time exploring approaches to conserve the newt until we know what to do about the crayfish,” he said. “That may require holding the newts somewhere outside the lake, like in captivity, until we have the technology to eliminate the crayfish. This summer, we started a pilot project with partners at the High Desert Museum in Bend to sort of evaluate this approach, and, so, we actually translocated about 20 Mazama newts up to the museum there to see if they could be raised and kept healthy in captivity. And the museum, I believe, is planning to put those on display as soon as they’ve figured out how best to keep them in their enclosures.”