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The crayfish invasion

Underwater barriers in Crater Lake are being floated as one idea to slow the invasion of millions of non-native crayfish that are threatening a salamander known as the Mazama newt.

“It’s still early in the invasion,” said Dr. Sudeep Chandra, a biology professor at the University of Nevada in Reno. “We’re talking about millions instead of hundreds of millions."

Crayfish were introduced to the lake by humans in 1915 to provide food for non-native fish. An explosion in the number of non-native species threatens not only the newt, but ultimately the awe-inspiring clarity of Crater Lake itself.

The metal barriers, which would be about 18 inches tall, would be installed along the lake bed at strategic spots, running perpendicular to the 21-mile-long shoreline, sort of like spokes in a wheel.

About two-thirds of the shoreline around the lake is now crowded with crayfish, so the barriers would be positioned to separate crayfish from the remaining newt habitats.

Chandra was chairman of a scientific panel that is working with Crater Lake National Park officials to find ways to slow down the crayfish invasion.

He said Lake Tahoe in California has an even worse infestation of crayfish. One of the strategies was to work with local companies to harvest the crayfish for sale as food, Chandra said.

By next summer, Chandra said the urgency of the problem at Crater Lake requires action be taken quickly. In the winter, the crayfish descend into deep waters but return to near the shoreline in the summer, Chandra said.

His panel suggested finding a way to sequester newt breeding areas just outside the lake. Installing the metal barriers, which likely would be made of aluminium, is another option but would require extensive environmental analysis.

Another conservation suggestion is to do a DNA analysis of the newts to preserve the information in case they don’t survive. “That shows how dire this is,” said Chandra.

Unfortunately, getting rid of the crayfish completely is almost impossible with current techniques, Chandra said.

Traps have lured in only limited numbers of crayfish.

The crayfish breathe through gills, and scuttle along the bottom of the lake.

Newts, which are about 8 inches long, were the top predators in the lake for thousands of years, gorging themselves on insects and snails. Now crayfish compete for the same food sources, and also intimidate and sometimes devour the delicate newt.

“You can hardly turn a rock over without finding a juvenile or adult crayfish,” said Mark Buktenica, the park's aquatic biologist. “We’re looking at barriers to slow down the invasion.”

Visitors wouldn’t see the barrier above the water line, Buktenica said. Scuba divers likely would install them but are limited to a depth of 30 meters, or about 100 feet. Crayfish have been found at 250 meters, or more than 800 feet, however.

Wizard Island is the location where crayfish were first introduced, and the barriers would be placed on either side of it.

“It’s probably the most viable option for slowing down the expansion of crayfish,” Buktenica said.

Crater Lake’s reputation for its crystal clear waters is also threatened, and it started a century ago by those working hard to keep the lake as a tourist destination.

“It’s ironic,” Buktenica said. “People who dedicated themselves to the preservation of Crater Lake were under the impression at the time that the introduction of these fish would make it a more desirable place for people to come.”

As the number of crayfish and fish increases, the delicate biology of the lake could be overwhelmed. Already scientists have seen an alarming jump in crayfish since 1980.

Buktenica said he hasn’t seen any signs of murky waters yet, but last year he noticed an increase in algae along the shoreline. As time passes and the biology of the lake changes, it could arrive at a tipping point that would be a disappointment to visitors, Buktenica said.

“We could see clarity issues along the lake,” he said.

Reach reporter Damian Mann at 541-776-4476 or dmann@mailtribune.com. Follow him on Twitter at @reporterdm.

The tiny Mazama newts are eaten by crayfish and compete for the same sources of food. Photo courtesy of National Park Service
Non-native crayfish at Crater Lake are spreading rapidly and threatening the Mazama newt. Photo courtesy of National Park Service