A small army aims to eliminate crayfish from the Santa Monica Mountains’ streams and rivers in 3 years

Source of this article: The Los Angeles Times, April 5, 2015

As the morning sun peeked over a mountain ridge on Saturday, Kyle Troy waded into a murky San Fernando Valley creek and hoisted a wire-mesh trap filled with angry crayfish aggressively waving their pincer-like claws.

“Native species don’t stand a chance against these guys,” she said, peering into the foot-long trap. “So we’re going to get rid of every one of them.”

When it comes to the nonnative 3-inch-long crayfish that has colonized and multiplied in the 109-square-mile Malibu Creek watershed over the last century, the 29-year-old biologist with the nonprofit Mountains Restoration Trust is merciless.

With a $600,000-grant from the California Department of Fish and Wildlife, Troy and a small army of volunteer students from local schools aim to eliminate crayfish from the Santa Monica Mountains’ streams and rivers — within three years.

This is an almost Sisyphean task. But it is an important part of an ongoing effort to transform the watershed’s ecological system into a more natural state, one that may eventually allow endangered steelhead to make their way back to historic spawning grounds.

The estimated 500 Southern California steelhead left on Earth are scattered across coastal waters between San Luis Obispo and the U.S./Mexico border.

“Crayfish are incredibly aggressive, and omnivorous,” Troy said. “They devour fish and insects, along with the eggs and tadpoles of frogs and toads. So they’ve got to go.”

Over the past year, the effort led by Troy and trust biologist Anders Reimer has trapped and removed roughly 44,000 crayfish, all of which were sent to the California Wildlife Center in Malibu, where they were used to feed possums and raccoons.

On Saturday, Troy and two dozen students from Pepperdine University focused on a 600-yard-long stretch of Medea Creek on the north end of the Santa Monicas.

The process involved checking the contents of 400 wire traps set a few yards apart in various locations of the creek bottom. They pulled up the traps, counted the number of crayfish in each one and emptied the catch into plastic buckets. Then they rebaited the traps with chicken-flavored dog food and returned them to the river bottom.

On a good day, Troy estimates this method can yield up to 600 crayfish.

Crayfish were introduced by anglers who used them as bait. Now they thrive where ever there is year-round running water shaded by oak trees, willows and brambles.

“I’m proud of what Kyle and her crew are up to out there,” said Lee Katz, a biologist at Pepperdine University who has studied local crayfish populations for two decades. “By removing crayfish, they are allowing precious native species from aquatic insects to newts and steelhead to rebound.”

Katherine Pease, a watershed scientist at the nonprofit Heal the Bay, was more blunt. “These crayfish, which are the same type folks like to eat at Cajun-style crayfish boils, are a huge threat to Southern California’s native aquatic species.”

“As a scientist, I find them somewhat charismatic,” she added with a laugh. “Personally, I do hate them.”

Troy would not argue with any of that.

Troy grew up in rural New York, where her love of ecological harmony began with excursions into forests near her home. In 2007, she earned a biology degree and went on to become a restoration biologist for the trust in 2014.

Removing the invaders from wilderness streams is arduous work. “But we’re making a dent,” Kyle said. “In areas cleared of crayfish, tree frogs are singing again.”

By 10 a.m. on Saturday, after a 60-minute campaign, the effort had removed 100 crayfish.

“By day’s end, we should have roughly 500 in the buckets,” she said, giving her crew an approving nod.

“That’s 500 crayfish down and several million to go,” she said, tromping back into the stream. “I honestly believe it’s doable.”