Crayfish in Crater Lake threaten native newt

CRATER LAKE, Ore. — Mark Buktenica, who’s worked as Crater Lake National Park’s aquatic biologist for 30 years, remembers times not so long ago when Mazama Newts, a species found only at Crater Lake, were common sights along the lake’s shorelines.

He says things changed in the 1990s, when sightings of the 8-inch long salamander, formally christened the Mazama Newt but affectionately called “mud puppies,” became less common. Instead, he and others found spiraling populations of nonnative crayfish, which had been introduced to the lake in 1915, ironically, to be food for the lake’s non-native fish.

“We kept seeing more and more crayfish,” Buktenica says. “And now you can hardly pick up a rock without finding one.”

Concerned about the shift, studies led by park aquatic biologist Scott Girdner, Buktenica and biologists from the University of Nevada, Reno, began in 2008. They’ve learned crayfish now occupy nearly 80 percent of the lakeshore. Newt populations, in contrast, have declined and face possible extinction.

“It’s not a compelling story until you see the impact on the newt species. It was the top aquatic predator in this lake for probably thousands of years,” says Girdner of why the population shift matters. “It’s alarming, especially when you consider that national parks are meant to protect the natural system. Unfortunately, the action of introducing crayfish a century ago makes protecting the native newt extremely difficult.”

Speaking up

Girdner, Buktenica and others are voicing their concerns in the scientific community. They’ve taken a PowerPoint presentation on the road and co-authored a study, “The Impact of Non-Native Crayfish on a Unique Population of Salamander in Crater Lake,” the Mazama newts.

It’s not known how newts found their way to the lake. Over hundreds, perhaps thousands of years, the isolated Crater Lake populations have become genetically distinct from other newts. Buktenica says the Mazama Newt is a type of rough-skinned newt, which feature brighter colors and are highly toxic. The Mazama variety are darker in color and less toxic, possibly because they have fewer predators because of their isolated habitat.

“Evidence supports the Mazama Newt as a sub-species,” says Buktenica, noting an official designation is pending. Whether that designation will matter is uncertain. The report offers little hope for Mazama Newts because of crayfish, which prey on newts.

Food chain

As a YouTube video shows, in a scene reminiscent of a horror movie, crayfish are voracious, efficient killers that eat newts. To survive, newt behavior is changing, sometimes resulting in being found in underwater areas where they are food for the lake’s non-native rainbow trout. The study includes a photograph of five dead newts taken from a gutted rainbow trout.

Not surprisingly, the reports notes:

“Newts remain in areas that crayfish have yet to invade but are almost entirely absent in areas occupied by crayfish … experiments conducted with newts and crayfish revealed that crayfish prey on newts, displace newts from under cover, and generally alter newt behavior when the two species co-occur. This evidence taken together suggests further crayfish expansion likely will cause additional declines in new abundance and distribution, and perhaps lead to extinction of the unique Mazama Newt.”

Crayfish distribution studies likewise give evidence of the spread of crayfish. A 2008 study found crayfish at 47 percent of the 39 study stations around the lake, with newts at 60 percent of the locations without crayfish. Only one site had both newts and crayfish. By 2013, crayfish had spread to 80 percent of the stations while newt numbers had drastically declined. In addition, snorkel surveys and baited traps at various depths found newts abundant in areas where crayfish were not seen. Recent studies, however, have found crayfish 820 feet below the lake surface.

Researcher worries

Biologists like Girdner and Buktenica have other reasons to be anxious; crayfish control efforts done at the Phantom Ship, a small lake island, proved ineffective. Teams used 35 traps to collect and remove crayfish during the past three summers. In 2012, 1,840 were collected. In 2013, 2,087 were caught. And this past summer 1,643 were taken.

“It had no impact at all,” Girdner says of removal efforts.

He’s also pessimistic because crayfish are located deep in the lake, which further complicates control efforts.

Girdner and Buktenica plan to hold workshops with others who have and are battling spiraling crayfish populations to see if they’ve been successful in control efforts. Both are hopeful, but not optimistic.

“That’s what we’re asking ourselves, what can we do?” Girdner admits. “We don’t know if anything would be successful. Will newts persist or be driven to extinction?”