Research shakes up oyster farming: UW professor strives to combat ghost shrimp using vibration, compaction

New research from a University of Washington scientist could give oyster farmers in Willapa Bay a fighting chance at battling burrowing ghost shrimp, little crustaceans that cause big problems. Biology professor Jennifer Ruesink published her findings last week.

Since 2023, Ruesink has been using a combination of subsurface vibration and surface pressure in designated areas in the Willapa Bay tidal flats to reduce burrowing ghost shrimp numbers.

“We realized we’re not chasing them away. We’re not vibrating them to death. What we’re doing is trapping them,” Ruesink said. “We have turned what was an adaptive value for them into a vulnerability.”

As ghost shrimp burrow they loosen the sediment, turning what was firm sand into soft mud. Oysters living in these sandy areas sink into the mud and suffocate. The proliferation of ghost shrimp has been devastating for oyster farms.

“I’ve lost a huge portion of my farm. Our carrying capacity for harvest-ready oysters used to be 235,000 bushels. My current carrying capacity is 75,000 bushels and that is 100 percent due to burrowing shrimp,” said Ken Wiegardt, a fifth-generation oyster farmer and head of Jolly Roger Oysters in Ocean Park.

A species native to Washington and more closely related to crabs than true shrimp, ghost shrimp became a problem in the 1950s because Columbia River dams keep fresh water from storm runoff and snowmelt from entering the bay, Wiegardt said.

“Now, there is not as much fresh water coming into Willapa Bay, which was kind of a natural control tool,” Wiegardt said.

For many years, farmers used pesticides — first carbaryl and then imidacloprid — to kill the shrimp. But in 2018, Washington’s Department of Ecology denied the permit for use of imidacloprid and other pesticides.

That same year, the state Department of Natural Resources staff began using special heavy amphibious tanklike buggies called Marsh Masters to repeatedly drive over the tidal flats to compact the sediment. The goal was to trap or kill the ghost shrimp in their burrows.

“They would just run back and forth across the ground and basically compact it. Yes, it would force the shrimp out of the burrows, but it completely destroyed the ground,” Wiegardt said.

Ruesink said compaction wasn’t as effective as pesticides. She said the efficacy was around 50 percent, far below the 90 percent and higher efficacy of imidacloprid.

Wiegardt said a family member tried a compaction approach using surplus Army track vehicles in the 1970s, resulting in a similar lack of success.

“You keep running over and running over the ground. Once (the shrimp) pops out, then you run them over and squish them. Or at least that was their line of thought,” he said. “Yes, it got rid of the shrimp, but the ground was unusable.”

Ruesink was attending a workshop when ghost shrimp and methods of eradication came up, and she realized it would be a good time to give vehicle compaction on a larger scale a try.

In the first year of her research, Ruesink worked with local oyster farmers to further test vehicle compaction but had little success. Realizing compaction wasn’t going to be a solution, she started looking for other nonchemical solutions. It was her husband, UW biology research scientist Alan Trimble, who gave her the idea to also try vibration.

“He said, ‘If you want to affect something that’s living a meter down, you can’t just scratch the surface.’ Which is what the vehicle was doing,” she said.

Ruesink began looking into the physics of how much water was being displaced — and the amount of surface pressure on the sediment — by the Marsh Masters, which are designed to create low surface pressure so they don’t get stuck in the mud.

“That amount of pressure liquefies the saturated settlement,” she said. “And a liquefied saturated settlement cannot crush a creature that’s living in there. It just allows that creature to sort of swim through the sediment.”

Ruesink and Trimble decided to try to re-create the vibration created by the Marsh Masters to see what impact that would have on the ghost shrimp. They decided to try professional vibrating tools used in construction to remove air pockets from cement. With the help of Trimble and their daughter Katie, Ruesink placed the concrete vibrators 1 meter down into the sediment.

But Ruesink soon discovered that vibration alone wasn’t having a lasting impact. She said the shrimp fled their burrows only to return a short time later. Then, she decided to combine vibration with compaction.

Ruesink and Trimble used a custom floating platform with an open center area designed to deploy six concrete vibrators into the sediment while applying the same amount of pressure of a person standing.

“We come back the next day, and there’s essentially no holes there. A few days later, we were checking it out, and the shrimp were mostly gone. At this point, we absolutely have no idea. Did we chase them away? Did we touch them and that vibrated them to death?” Ruesink said.

Core samples taken after two days found the shrimp had been trapped in their burrows and died. Testing completed at four sites reduced ghost shrimp densities by 72 to 98 percent, which is comparable to pesticide use, according to the research data.

Despite the seemingly positive results, Ruesink said it will take time and money before local farmers will be able to treat their oyster beds using this method. She said treating 100 to 200 acres a year would be enough to help keep Willapa Bay beds in production.

She and Trimble estimate it would take $2 million to design and build a farm-scale apparatus that could treat a couple of acres at high tide.

Ruesink said she is looking for grant funding to make the transition from research to production.

“I am on the lookout, especially for (U.S. Department of Agriculture) sources that might invest in this because of our value to commerce and food security in the U.S. given that Willapa Bay is such a huge contributor to U.S. oyster production,” she said.