They’ve tried smashing, cementing, shocking and shaking them, but now that pesticides are off the table — at least temporarily — what’s the option for ridding oyster beds of ghost shrimp?
LONG BEACH,Pacific County— Ever since the shrimp hit the fan this spring, Kim Patten’s life has been a whirlwind.
Calls and emails from politicians, business leaders and anxious shellfish growers started flooding the tiny Washington State University research station Patten runs on Willapa Bay. Endless rounds of meetings ensued. The university even summoned him to the Pullman campus to huddle with administrators and deans.
Everyone is asking the same question, Patten said. “What are you going to do about it?”
Scientific name: Neotrypaea californiensis
Habitat: Coastal estuaries
Animal type: Invertebrate
Diet: Plankton and detritus
Size: 4-5 inches
Lifespan: Up to 20 years
Range: Alaska to Baja California in the intertidal zones or mud flats. It’s native to estuaries along the West Coast.
Fatal to oysters: Ghost shrimp don’t directly kill oysters. But their burrows — up to 100 or more per meter — soften the ground and oysters sink into the mud and die.
Source: Monterey Bay Aquarium
To which he can only shrug.
Over the past 13 years, Patten has tried every method he could think of to control the crawfish-sized invertebrates called ghost shrimp that threaten the famed oyster farms of Washington’s outer coast.
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Zapping the creatures with electrified spikes didn’t work. Neither did injecting habanero-pepper extract into their burrows, crushing them with heavy machinery or blasting them with high-pressure water jets.
Patten thought he had the problem licked when the state Department of Ecology (DOE) approved a plan to spray tidelands with a neurotoxic pesticide. Called imidacloprid (ee-mid-uh-cloe-prid), the chemical paralyzes the shrimp so they suffocate in their muddy holes.
But neither Patten nor shellfish producers were prepared for the critical media coverage and public backlash that followed. Celebrity chefs in Seattle were horrified. Shellfish buyers threatened to cancel orders, and consumers took to social media to express outrage over the use of pesticides in pristine estuaries.
Taylor Shellfish, the state’s biggest producer, quickly backed out of the plan and pledged not to spray its oyster beds. The Willapa-Grays Harbor Oyster Growers Association (WGHOGA), which includes many smaller oyster growers, bowed to public pressure two days later and canceled its pesticide permit.
Now, Patten is racking his brain for what to do next.
“I’m not going to retire until I solve this problem,” said the 62-year-old agricultural extension specialist. “But I might be here until I’m 99.”
Patten has been reviewing the results of previous experiments, looking for nonchemical alternatives and new cultivation methods that might be worth another try. He and other researchers are also exploring ways to target shrimp in a more vulnerable stage of their life cycle.
But it’s not clear that the entire shellfish industry has given up on the chemical route.
Stung by the bad press, members of WGHOGA closed ranks and hired a public-relations firm. In recent meetings with DOE, they raised the possibility of modifying their plans and applying for another permit to spray.
“They haven’t made the determination yet on how to move forward,” said India Simmons, of PR Ink, who is acting as the group’s spokeswoman. “They are trying to figure out if they can stay in business.”
Tide flats turned to goo
As the tide receded on a breezy afternoon, Patten led visitors onto an expanse of mud flats on the edge of Willapa Bay. Along with Grays Harbor, to the north, this vast, shoalwater estuary accounts for a quarter of all oysters farmed in the U.S.
Wearing a red Cougs cap and jeans tucked into scuffed rubber boots, Patten pointed out the mounded burrows that dimpled the mud. “Those are ghost shrimp,” he said.
He plunged a long metal tube, called a shrimp gun, into one of the mounds and pumped a plunger to suck out its occupant: a pink female, about 4 inches long, with a cluster of eggs on her abdomen.
“She’s probably 6 to 10 years old,” Patten said. “And she can live another six to 10 years.”
For an oyster grower, the problem with ghost shrimp is that they turn tide flats into goo as they churn up sediment to feed on algae and microbes. Where shrimp populations are dense — 100 burrows per square meter aren’t uncommon — oysters sink into the mud and die. People sink, too, said Patten, who has rescued colleagues mired up to their thighs.
The shrimp aren’t interlopers in this ecosystem, though. They’re native to estuaries along the West Coast and serve as food for everything from salmon and sculpin to Dungeness crab, herring and gray whales.
The region’s original human inhabitants probably ate them, too. Patten cooked up a batch, but found the taste bland and the texture mushy.
The shrimp weren’t considered pests until over-harvesting wiped out native Olympia oysters, which formed thick reefs impervious to burrowing. Complaints started in the 1920s, soon after growers imported Pacific oysters from Japan and adopted the farming method prevalent today: scattering a single layer of oysters directly on the tide flats.
In the 1950s, shrimp populations exploded. Scientists don’t really know why, but they suspect a convergence of man-made and natural circumstances like warm ocean temperatures, siltation from logging and overfishing of predators like herring and sturgeon. Construction of dams on the Columbia also eliminated freshwater surges believed to have killed off the shrimp.
Growers responded with a 1950s-era solution: a potent pesticide called carbaryl. A neurotoxin classified as a likely human carcinogen and banned in many countries, carbaryl also kills fish and other marine creatures. Yet for decades, growers sprayed it on oyster beds with little public outcry.
“I was told it was OK, that it was the same chemical in flea powder,” said Oysterville shellfish farmer Dan Driscoll. He quit spraying when customers at his retail shop started raising concerns.
“They were appalled that anyone would spray chemicals on the tide flats of an area that is considered the most pristine estuary in the Western United States,” he said.
Environmental groups eventually sued, and growers agreed in 2002 to phase out carbaryl over the next decade. That’s when Patten was recruited to help find an alternative.
Though critics call him “Chemical Kim,” Patten’s original goal was to control shrimp without conventional pesticides.
He tried applying a thin layer of concrete to the tide flats, but the shrimp burrowed through before it hardened. He tried blowing them up by injecting a propane mixture into their burrows. It wouldn’t ignite.
Patten and his colleagues tagged shrimp to track their movements and spied on them with underwater cameras. But the adults rarely venture out of burrows up to 3 feet deep. Electroshocking, which drives earthworms to the surface, spurred the shrimp to dig in.
When dozens of “green” chemicals, like the chili extract, ground mustard seed and clove oil, also failed, Patten reluctantly turned to conventional pesticides. “The last thing I wanted to do was go down this road we’re on now,” he said.
But he and the growers thought imidacloprid would be welcomed as a more benign alternative to carbaryl. It’s less toxic to fish, dissipates quickly and is applied at less than one-tenth the concentration.
Some environmental agencies were not pleased, though, pointing out that the pesticide had never before been approved for aquatic use and warning of possible collateral damage to crab and other wildlife.
DOE issued the permit in April. Spraying was set to begin in May.
Now, for the first time in nearly 60 years, oyster growers find themselves with no chemical weapon to deploy in their battle against ghost shrimp.
Pesticides generally aren’t allowed on shellfish beds in Puget Sound. Some growers on the Pacific Coast have never used them, either.
“You can have aquatic diversity and still farm your crops,” said Erika Buck, on a recent visit to the 140 acres of Grays Harbor tidelands where she harvests about a million oysters a year.
Splashing through calf-high water, Buck pointed out undulating eel grass, sand dollars, cockles, crabs, young oysters — and ghost shrimp — thriving side by side. “You wouldn’t have been able to walk on this when we first leased it,” she said. “There were so many shrimp you would just sink in the mud.”
To keep the shrimp in check, Buck uses a technique called harrowing — dragging an oversized rake behind a boat. The tines dislodge the shrimp and fish pounce.
“When the shrimp are exposed, the fish are eating them like crazy,” she said. “You can see the scales flashing in the water behind the harrow.”
But the process is costly, time consuming and must be repeated frequently. “It’s not a quick fix,” Buck said.
Pesticides are, which is why Buck thinks many growers use them.
“It’s just a mindset, and they aren’t looking past it,” she said.
But Patten bristles at that claim.
Many growers in Willapa Bay face denser shrimp populations than in Grays Harbor. And many have been experimenting with alternative approaches, he said.
On the Willapa tidelands, Patten pointed out several methods to elevate oysters above the sediments, including mesh bags hung from stakes. The tide flips the bags and tumbles the oysters inside, resulting in uniform specimens for the half-shell market. Other growers suspend their oysters on long lines.
But those methods only work in sheltered areas of the bay, where winter storms won’t rip them to shreds. And if the ground is riddled with too many shrimp burrows, anything suspended will simply topple over. Off-bottom culture is also unsightly, with PVC pipes, ropes and stakes.
Since Driscoll stopped using pesticides, he’s been able to rotate his crops and keep shrimp to manageable levels by driving an ATV across the tidelands to compact sediments and crush the burrows.
For growers with less land and more shrimp, that approach wouldn’t work.
“The shellfish farmers are not exaggerating when they say their beds are threatened by ghost shrimp,” Driscoll said.
Lots of “solutions”
The ultimate solution will probably lie in new culture methods, Patten believes. He and other scientists also plan to revisit some of their earlier ideas, such as testing whether fresh water is, indeed, fatal to shrimp or if boosting natural predators might help. There’s even a small effort under way to see if native Olympia oysters could be reestablished.
Patten has been fielding lots of calls from folks who think they have the answer. One entrepreneur said he could create an army of tiny robots to attack the shrimp. A more promising suggestion came from a pair of University of Washington researchers, who say low-frequency sound might drive the shrimp to the surface.
Brett Dumbauld, a U.S. Department of Agriculture (USDA) researcher who has spent a lot of time unraveling the shrimp’s life cycle, thinks it might be possible to target juveniles when they’re tiny and haven’t yet built large burrows. He’s also been tracking shrimp densities for two decades, and points out that growers have been relatively lucky in recent years.
After a boom in the 1990s, shrimp numbers dropped steeply because few offspring survived a larval stage in the ocean. A parasite has nearly wiped out a related species called mud shrimp. But over the past two years, more young ghost shrimp have returned and densities are starting to climb.
Big companies like Taylor Shellfish can shift production from beds with heavy shrimp levels and invest in new culture methods, Patten said. Small, family operations lack that flexibility. As long as shrimp densities remain moderate, most should be able to limp along, he predicted. But if the population spikes, many will be in trouble.
“Will 50 percent go out of business?” he asked. “Ninety percent? We don’t know.”
Because their livelihoods depend on clean water, oyster growers have long led the battle to protect coastal estuaries from pollution and development. But a recent editorial in Long Beach’s Chinook Observer pointed out the contradiction between that philosophy and the use of toxic chemicals. “This conflict between lofty aspirations and pragmatic necessity has now blown up into an existential crisis for the mainstream oystermen of Willapa Bay,” the paper said.
The chances that a new imidacloprid plan, or use of another pesticide, will be acceptable to the public is slim, the editorial continued. That means the industry is facing a fundamental shift.
In order to make that transition, growers will need support from the state and those who value a clean environment and local seafood — or the region’s small shellfish farms could vanish, the paper warned.
“Without its scrappy, hardworking and diverse army of oyster growers … the bay may be saved from pesticides but lost to everything else.”