Rapidly reproducing pest wreaks havoc on native species
In Asia, they're considered delicacy.
In America, they're considered deadly.
Fortunately, only one of them has been discovered so far in the Columbia River region - and new laws are aimed at keeping any more out.
But fears still loom that the Asian mitten crab, an invasive migrating crustacean, will bury its furry claws into the Northwest's economy and precious waterways.
Named for the thick clumps of hair that cloak its pincers, the crab is the target of research and educational efforts along the West Coast.
Researchers in the Northwest are especially focused on the Columbia River, where they fear the creature - which spawns in salt water and can migrate hundreds of miles up freshwater rivers - could wreak havoc similar to damage already caused in California waters.
The unwelcome alien first arrived in the San Francisco Bay in 1992. Within a decade of its discovery, nearby rivers and fisheries have been devastated with clogged fish screens, eroding banks and levees, and marred commercial fishing nets.
Researchers have confirmed that the crabs eat steelhead eggs and suspect them of eating salmon, sturgeon and trout eggs as well.
"They're really one of the last things we want to see in the Columbia," said Toni Pennington, aquatic nuisance species research assistant at Portland State University's Center for Lakes and Reservoirs. "Salmon already have enough problems around here."
The crabs are also known to carry the oriental lung fluke, which can be passed to humans and causes symptoms similar to tuberculosis.
Pennington and others at PSU are working to ensure that if the crab makes it to the Columbia, someone notices. She's traveled much of the Oregon Coast posting "wanted" signs for the species, which urges anyone making a discovery to kill it and report it to Oregon's invasive species hot line: 866-INVADER.
With female mitten crabs carrying between 250,000 and 1 million eggs, "even seeing one crab is a serious alert," Pennington said.
California's San Joaquin Delta is a frightening example. Four crabs were discovered in the delta in 1996. By the following year, their population was estimated at about 20,000. From there, the numbers burst even further with the highest counts coming in at around 15,000 per day in 1999.
"It's true, they can produce in horrendous numbers under the right conditions," said Jim Bergeron, a retired Sea Grant extension agent from Svensen, who's helped with local monitoring efforts.
"(But) there really isn't a whole heck of a lot you can do if they do show up here," he added. "The focus is prevention and testing to give people warning."
Last year, Bergeron suspended a mitten crab trap, forged out of a milk carton and PVC tubes, off the docks behind the Columbia River Maritime Museum. But after checking the trap over a few months, he never caught more than a few crawdads, he said.
Today, four teams of nine volunteers intermittently check traps located around the lower Columbia and tributaries as they have since late 2001. Earlier last year, a PSU researcher regularly sampled 50 separate locations with baited traps, also in and around the lower river area, Pennington said.
Although the creature can be difficult to catch, all efforts so far have hinted that the crab has yet to wrap its pincers around the Columbia River.
But that's not to say anyone is letting down their guard.
Efforts are also being leveled at fishermen who likely have the best chances of accidentally snagging one or spotting one of its burrows.
"In most cases, it's the public, like a fisherman, that finds one and says 'hey, what's this?'" said Scott Smith, aquatic nuisance species coordinator with the Washington Department of Fish and Wildlife. "Those are the people we're counting on."
Fisheries groups are also readily offering their assistance.
"When an invader comes into a new territory, it reaches beyond a single species," said Stephen Phillips with the Pacific States Marine Fisheries Commission. "When people hear that these things eat salmon eggs and can migrate 600 miles upriver, that gets them pretty interested. That's what we want - people interested."
Fears rose briefly in 1997 when a lone mitten crab was caught near Sauvie Island, just west of Portland. Although the species are said to be difficult to distinguish, the crab was "Japanese," as opposed to the "Chinese" mitten crabs that have plagued California. Smith said little is known about differences, if any, in the two species and their effects on non-native fisheries.
Researchers are also uncertain how either of the crabs ended up in the U.S. in the first place. A few suspect those in San Francisco Bay were intentionally planted in the area by someone interested in sparking a mitten crab fishery. Others think they were more likely discharged with a visiting ship's ballast water.
Up until last year, transpacific ships were asked to exchange their ballast water, voluntarily, at least 200 miles from shore. But only about half of the incoming ships were reportedly complying. In June, the state Senate, following the lead of California and Washington, made the exchanges mandatory.
"That's a start," Smith said. "But (along with our educational efforts), we're mostly just keeping our fingers crossed that we don't see them here."