Invasive crayfish in Oregon devastate native newts

At Crater Lake, the National Park Service is seeking solutions — but it could be too late.

 

In 1888, William Gladstone Steel, a dapper Portland mail carrier, dumped 200 fingerling trout into a tin bucket and set out to create a national park.

Steel toted his cargo 49 miles to southwest Oregon’s Crater Lake, where he released 37 surviving trout into the indigo oasis. His motives were pure: By enhancing Crater Lake’s recreational value, he hoped to strengthen the rationale for protecting it, a campaign that had become his obsession. By 1901, tourists had begun catching trout grown to the length of baseball bats. The next year, Crater Lake was designated a park.

Yet Steel’s fish-stocking, however well-intentioned, also set in motion a slow-moving ecological catastrophe that, if left unchecked, could end in the extinction of a native species. That may seem unsurprising, as introduced trout have wreaked havoc on countless alpine lakes. In Crater Lake, however, the trouble isn’t fish — it’s fish food.   

In 1914, nearly three decades after his first fishy experiments, Steel, now Crater Lake’s superintendent, came up with another ecologically dubious idea. The fish, by then, had ceased flourishing; Steel thought they might be starving. At his behest, the park imported 15,000 armored, rust-colored crustaceans — Pacifastacus leniusculus, the signal crayfish.

Though the signal crayfish is native throughout much of the Northwest, it doesn't belong in Crater Lake. Photo courtesy of Washington Department of Fish and Wildlife.

Over the past century, crayfish — aka crawfish, crawdads, or, if you study invasive species, “aquatic cockroaches” — have colonized lakes and streams from California to Taipei. In some places, as in Crater Lake, they were introduced deliberately to control weeds or feed fish; in others, they arrived accidentally as bait. They are, in many respects, the perfect invader: hardy, omnivorous, aggressive. “They have those big claws, and they’re really good at essentially brutalizing other animals,” says Jake Vander Zanden, a professor at the University of Wisconsin-Madison who has waged war against crayfish in midwestern lakes.

You don’t need to be an ecologist to guess what happened once the disastrous decapods arrived at Crater. The fish didn’t eat them, and all but two species (rainbow trout and kokanee salmon) eventually perished. The crayfish, meanwhile, persisted in the lake at low levels until the 1990s, when populations exploded — perhaps thanks to climate change, which may have warmed Crater Lake’s waters enough to stimulate rapid breeding. As the crustaceans boomed, they devastated aquatic invertebrates, like worms and midges, which plummeted by nearly 80 percent in infested areas.

Unfortunately, aquatic insects are also the preferred prey of the Mazama newt, a proposed subspecies of rough-skinned newt found only in the Crater Lake basin. Not only did the crawdads outcompete the newts, but when ecologists stuck the two critters in the same tank, the crustaceans sometimes killed and devoured their cohabitant. (As with, say, New Zealand’s flightless birds, the newt’s historic isolation from predators may have been its downfall: While rough-skinned newts elsewhere produce a powerful toxin, the Mazama newt possesses no such defense.)

When Park Service ecologists surveyed the lake in 2012, they documented a disturbing but unsurprising trend: Where the crayfish were present, the newts were absent. These days, a full 80 percent of the lake shore, and counting, is effectively off-limits to amphibians. Attempts at removing the crayfish via trapping have failed utterly: Their populations just seem to come back stronger.

“It’s depressing, to be honest,” says Mark Buktenica, a Park Service aquatic ecologist who has worked at Crater Lake since 1985. “We’ve been successful in preserving and protecting the Crater Lake that you see from the rim. But in our naiveté, we’ve created a situation that’s irreversibly altering the ecosystem within the lake itself.”

The Mazama newt, a proposed subspecies endemic to Crater Lake, is threatened with extinction. Photo courtesy of Lee Kats.

In early August, the Park Service called in the big guns, convening a cohort of newt and crayfish experts from around the country to discuss the agency's options. The mood was sober, the alternatives sparse.

“In an ecosystem of this size and complexity, it’s not likely that crayfish can ever be eradicated,” says Sudeep Chandra, a biologist at the University of Nevada-Reno who was among the workshop’s leaders. The Park Service’s only recourse, Chandra says, “is to keep the invasion front from expanding rapidly.”  

So how do you prevent crustaceans from infiltrating the final untouched stretches of Crater Lake’s shoreline? The panel’s consensus: build a wall. According to Chandra, the workshop recommended the construction of foot-high fences, likely made of aluminum, sunk into the lakebed. Crayfish, it turns out, far prefer to crawl along the bottom than to swim in the water column; therefore, even a low barrier acts as an impediment. Perhaps the walls could be used to establish a refugia, a section of lake where the Mazama newt is relatively secure from assault. (The panel also suggested installing crayfish traps along the fencelines to fortify the preserve, as well as investigating the viability of natural refugia, like springs and isolated shoreline ponds that support newt larvae.)

“Even if you can never remove crayfish completely, a barrier will slow them down and give amphibians a chance to reproduce,” says Lee Kats, a biologist at Pepperdine University who attended the workshop, and who has deployed mesh fences to block crayfish from invading stretches of California streams. “We’re going to have to think more creatively than ecologists are used to thinking.”

Crayfish have effectively excluded newts from much of Crater Lake. Map courtesy of National Park Service.

But conservation takes money, and Buktenica says funding schedules will likely prevent the Park Service from installing barriers for at least two years. Trying to list the Mazama newt as an endangered species could help galvanize action. Ultimately, though, Buktenica fears that the only way to save the amphibian may be to pluck survivors from the lake and breed them in captivity. The newt, then, has become what biologists call a “conservation-reliant” species — one that requires aggressive human management to avoid going extinct. 

All of it makes you wonder what William Steel would say, were he around to witness the impacts of his crustacean stocking. In defense of Crater Lake’s founder, Steel introduced crayfish before the dawn of invasion ecology. Still, the blunders of our forefathers cast long shadows, and Steel’s innocent error won’t be easily remedied. “I was really hoping we could identify some hopeful, positive management strategy,” Buktenica says. “But we haven’t found it yet.”

Ben Goldfarb is a correspondent at High Country News.