Perfect Invaders: How Crayfish Are Threatening Crater Lake's Smallest Creatures

Biologist Mark Buktenica scours the shoreline of Crater Lake. He scans white sun-bleached rocks, takes a step, flips a rock.

Scan, step, flip.

Downed flying ants coat the surface of the water. A lizard hunts nearby. Small grey-green toads, about the size of a quarter, hop out of his way.

Scan, step, flip.

“Good candidate, perfect rock, but no salamanders,” he mumbles under his breath.

Dozens of times he repeats. Then dozens more as the rocks shift and clank under his boots. The salamander Buktenica is looking for is rare. In fact, it only lives here, in the shallow coves of Crater Lake.

Finally, the search pays off.

“The Mazama newt. Found no place else in the world,” Buktenica says as he places a 3-inch long orange-bellied newt in the palm of his hand.

Crater Lake formed nearly 8,000 years ago, after Mount Mazama erupted and the caldera began filling with snow and rainwater.

“We don’t know when newts entered the caldera but some time thousands of years ago,” says Buktenica, who’s worked at Crater Lake National Park for nearly 30 years.

There were no fish or other predators in the newly-formed lake, and the Mazama newt expanded and thrived. It was the undisputed top of the food chain.

But not anymore.

A new champion

Out on the Crater Lake research vessel Neuston, Buktenica has his hand on the controls of a large winch. He leans over the side of his research boat, looking far down into the clear depths of Crater Lake.

“Sight!” he yells. “We’ve got the anchor and the trap coming up.”

Shore is only a few hundred yards away, but it’s really deep here – more than 800 feet of water below the boat. The winch is pulling in two cylindrical wire crayfish traps from the bottom. Astoundingly, they’re full.

“I see crayfish!” he says.

“Get outta here,” says Scott Girdner, another biologist at the Park.

“Son of a monkey’s uncle,” Buktenica swears, slowly shaking his head.

Girdner says these are the deepest known crayfish in any lake system in the world. And they’re an ominous sign of just how far the invasive species has spread.

The story of the crayfish in Crater Lake begins more than 100 years ago - back when getting to the future national park from Medford took five days by horse and wagon. To attract visitors, early conservationists began stocking the lake with game fish like trout and salmon

“In the past the national parks have done many things which people thought were good ideas at the time that turned out to be not so great ideas,” says Park Superintendent Craig Ackerman.

In 1915, park managers introduced the signal crayfish from surrounding Northwest lakes to feed those fish.

“And that turned out to be a worse decision than stocking the fish in the first place, because the crayfish have become out-of-control,” he says.

Turf war

Scientists at the park are finding that crayfish and Mazama newts don’t really get along.

“Where crayfish occur, we don’t find newts. And we only find newts where there are no crayfish,” Buktenica says.

Not only do they compete for the same food, but studies at the park show crayfish chase and harass the newts, causing them to flee. And in some cases, the crayfish prey upon the newts.

“They’re virtually the perfect invader,” Buktenica says. “They eat algae. They eat plants. They eat aquatic insects and worms and snails. They’ll eat amphibians. They’ll eat small fish, they’ll cannibalize their own. And they’ll eat dead and decaying fish as well.”

Conversely, the Mazama newt is the ideal prey. After thousands of years evolving without predators, the newt lost its best weapon: a potent neurotoxin that can kill.

“With the loss of its toxicity, it’s left virtually defenseless,” Buktenica says.

And that’s not all, says John Umek, a PhD candidate at the . He’s been studying the effects crayfish have on other animals in the lake.

“At these areas where we don’t have crayfish, we have a ton of different species of organisms,” Umek says. “We have lots of snails, lots of caddises, mayflies. And when crayfish come in, a lot of those just disappear.”

These disappearing invertebrates eat algae that can cloud what is currently one of the clearest bodies of water in the world.

“One would think at a beautiful lake like Crater Lake, with nice blue water with very little algae, you'd want to keep algae away,” says Sudeep Chandra, another researcher at UNR.

Why now?

Despite their current offensive, crayfish in Crater Lake weren’t thought to be such a problem until relatively recently. Surveying started in 2008 and scientists found newts had the advantage, occupying about half the shoreline. The crayfish occupied most of the rest.

But just six years later, in 2014, the crayfish had taken over more than 75 percent of the shallows. And once the crayfish move in, the newts vanish.

Biologists suspect that the recent rapid expansion is the result of several factors. One theory is that the population has been increasing steadily all along, but it wasn’t until the past couple decades that crayfish finally reached carrying capacity in the areas where they were originally introduced.

“It’s the tipping point,” explains Umek.

There’s only enough food and shelter for a certain number of crayfish, and once that’s reached, crayfish either move out or starve.

Girdner suspects that climate change is also playing a role. The surface temperature of the lake has increased about three degrees in the past 10-15 years. It's risen by five degrees overall in the past half-century.

“It may just allow the crayfish to move faster. They’re just more active at warmer waters,” Girdner says. “And it may allow them to have more successful reproduction.”

Slowing the advancing army

The team at Crater Lake surveys for crayfish each summer. They set and pull traps all along the shore, and deep into lake. They count, weigh and measure their catch. And they tag and release some to find out how they travel.

It’s all part of trying to figure out how fast and where the crayfish are expanding. And where their advance can potentially be slowed or halted to give the newts a chance.

“It’s very possible that the Mazama newt would be eliminated from the lake if we didn’t do anything,” Girdner says.

But at this point no one knows exactly what to do.

Trapping, even intensive trapping, hasn’t made a dent. In one location, biologists trapped and removed more than 5,000 signal crayfish over a three-year period. Yet the overall population just kept increasing.

“Removal in a lake of this size and this complex of habitat is just not feasible,” Girdner says.

Despite this, there there are a few glimmers of hope for the Mazama newt. That’s where UNR’s Chandra comes in. He’s leading a panel of specialists in the science of crayfish, newt and invasive species. They're charting possible paths forward for the park.

“Crayfish are expanding along an invasion front, kind of a wave of army moving along the shoreline. Their movements are so quick,” Chandra says.

He says the best thing to hope for is to slow or halt their advance. One possibility is installing underwater fencing around newt-only areas to keep the crayfish out. It wouldn’t have to be high, because crayfish don’t usually swim – just a foot and a half of metal flashing running straight out from the shore.

But this option has drawbacks – like the possibility the fences would negatively impact the visual aesthetic of the lake. Another big question is just how much fence would need to be run? And how deep? Consider the crayfish being found at 800 feet.

“What are those crayfish doing down at 250 meters? Are they lost to the population? Is it a one-way street going downhill and they don’t come back up?” Buktenica asks.

If they do crawl back into the shallows, the crayfish could just go around the deep edge of any underwater fence.

To try to answer these questions, park scientists have devised a plan. In the cabin of the research boat, Scott Girdner holds a four-inch long crayfish, belly-side up. In the other hand, he holds a syringe filled with a bright blue substance. It looks like plastic.

“The idea with this polymer is to inject it underneath their abdomen,” he says. “And that polymer will harden and it’ll stay even through multiple sheds.”

The crayfish waves its claws as Girdner tags it with a small but visible line of blue. The tagged crayfish will be released back into the depths and in the years to come the scientists will see if they show up again in the shallows.

But time is running out for creatures like the Mazama newt. Without intervention, this unique creature could vanish from the lake within the next few decades. Steps to slow the crayfish down will likely need to be taken before this tagging will yield significant results.

“We may be to the point that there’s not a whole lot else we can do. It’s kind of a depressing situation because as a scientist you want to do something,” Girdner says. “You want to do something to preserve that unique species that occurs only in Crater Lake.”

Newt refuges?

Another conservation possibility could be provided by the lake itself – in isolated spring-fed pools located along the caldera shore.

Each summer, the pools emerge when rock and snow avalanches scour out depressions, pushing the displaced rocks and dirt up into berms along the shore. This creates a natural seawall separating the pools from the main lake. Because of their isolation and the fact they’re not visible from lake, very few people have ever seen these pools. But it’s this isolation that makes them perfect newt nurseries.

“They’re used pretty widely by newts and other amphibian for breeding and rearing,” says Buktenica. “They’ll come into these pools while there’s still snow on the edges of the pool.”

The conservation promise is that while newts move across land to get to the isolated pools, signal crayfish do not. It’s not a perfect solution, because some years the water level in Crater Lake rises and breaches the seawall, giving crayfish access.

“If we can maintain those small pools as refuges and crayfish free, perhaps we can have enough reproduction to keep the population going,” Buktenica says.

'Winning'

The sobering reality is crayfish will likely never be eliminated from Crater Lake.

“We're going to win on this one by looking at the details and by exploiting the side areas that are crayfish free,” says Pepperdine University biologist Lee Katz, a member of the independent scientific panel working with Crater Lake National Park.

“And by winning I mean promoting co-existence here for a long time.”

This rather dismal definition of what success would look like is a common sentiment at the park. But even this may be more aspirational than realistic.

Controlling the signal crayfish and protecting the unique ecosystem of Crater Lake will be labor intensive and expensive. But Crater Lake Superintendent Craig Ackerman says the National Park Service’s mission and mandate are to protect the entire lake system.

“So we will put the resources into this that we feel necessary,” he says.

Whether it’s underwater fences, preserving and protecting the natural pools or something else, scientists say acting quickly is key.

“We have the opportunity right now to potentially at least slow down the invasion of crayfish,” Umek says. “If we miss this opportunity, I think it’s going to be a lot of trouble for the newts.”

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