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Combating Snails To Save Oysters

NAHCOTTA — Imagine you’re an oyster laying snugly in your bed in Willapa Bay, filtering in nutrients while growing to two and a half inches in diameter. And then you feel a weight on your quarter-inch thick shell and a short time later you begin to hear a grinding sound.

Slowly, inexorably over the next few hours the drilling continues as the radula (a sandpaper-like tongue) of an Atlantic or Asian oyster drill snail takes away debris that its secretions of hydrochloric acid has created on your shell. When the snail inevitably pokes through your shell, its proboscis makes you its next meal.

“Oyster drills are definitely a problem. It depends on where you are at on the bay as to how bad they are. They like barnacles better, but they kill a lot of oysters and the only way you can get rid of them is to go hand pick them,” oysterman Brian Kemmer explains. 

“Oyster drill snails are costing oystermen millions of dollars in Washington state and we are on the fast track to see what we can do to stop the devastation,” Steve Sylvester, Ph.D. from WSU-Vancouver, said. He and a cadre of students and assistant John Anderson have been studying to find a way to eradicate the invasive oyster drill snail through a grant from state sales of oyster reserves.

Accidental invader

The Oyster Reserve Advisory Board hired Dr. Sylvester (Ilwaco High School, 1968) and his crew in hopes of finding a way to eradicate the oyster drills. The snails came to Willapa Bay many years ago when oyster seed was imported from Japan and from the East Coast.

“At first, oyster growers tried to keep the drills in one place, but now the snails are everywhere that there are oysters, both in our state and world-wide,” Sylvester says. “They consume oysters up to two and a half inches in diameter. They eat about one oyster every three days, and they are extremely efficient at what they do. The Asian drills are larger (about an inch and a half long), inhabit the north end of Willapa Bay, love to climb, and the males and females aggregate when they lay their eggs, while the Atlantics are a half inch shorter, they are found in the south end of the bay, and they do not tend to climb or aggregate.”

Eric Hall of Taylor Shellfish Co. put out a test of about 500 bags of seed that included about 50,000 spat or nickel-sized young oysters. The bags were placed on property they own in the Smoky Hollow area south of Long Island. The area had been notorious for having Atlantic oyster drill snails. “Within two weeks every oyster was dead and they all had a hole in them from the oyster drills,” Hall said.

“We own about 6,500 acres in Willapa Bay and about 500 acres of that is infested with oyster drills so that we cannot produce oysters. Another 5 percent of our costs go to trying to get rid of the drills because we have to be very careful to wash our tubs used in high concentration areas. Oyster drills are everywhere in the bay, but are worse in some places. They have a huge economic impact here and in Puget Sound.”

Biologist Bruce Kauffman at Willapa Bay Field Station in Nahcotta says, “We have loaned a live tank to Steve Sylvester. Since we haven’t had a large natural oyster set throughout the bay in (seven) years, the number of oysters is down, while the number of drills fluctuates from year to year, but is about the same. The drills are where the oysters are and that can be on some of the most productive hummocks.”

Trying all the options

Dr. Sylvester has tried an arsenal of strategies to eradicate oyster drill snails. “I am a toxicologist (professor of molecular bio-science) so I don’t use the ‘spray’ word lightly. If we do use a molluscide we want it to be something that will get rid of the invasive species, in this case the oyster drills, and not harm other organisms or human consumers,” he explains.

One problem the researchers from WSU are facing is that what works in their laboratory water tables in Nahcotta and Vancouver doesn’t work in the ever-moving waters of Willapa Bay. A group of four engineering students developed a trap for the snails that is effective in catching them, while keeping crab from eating the bait.

While using ocean mussels, various chemo-attractants, and pheromones for bait has worked well in laboratory settings, it has not attracted significant numbers of oyster drill snails to the traps in natural settings in the bay. Sylvester and his crew have developed a labor-intensive method of PIT-tagging (passive integrated transponders) or gluing a chip to each snail in their study. Using a detector, the scientists then can find and track snail movement in the bay.

“Using the chips is a whole lot easier and more efficient in finding snails to a depth of four feet, than trying to look for them,” Sylvester says.

Natural alarm system

Something that has been discovered about oyster drill snails is that when one of them is injured it gives off certain chemicals; other snails in the laboratory that are near by will then either move away or stop feeding. Unfortunately the PIT-tag method of following the snails has not shown the same positive results in the bay. “It would be nice to distress one snail and have all the others leave an area or at least stop feeding, but that hasn’t proven to be the case,” Sylvester relates.

Natural barriers such as mud flats, or in the case of Atlantic oyster drills, making the snails climb, has proven somewhat successful in containing them. Young oyster drills tend to feed on barnacles and the idea of using “marine glue” on barnacles to catch the snails is another option being tested.

Using absorbent fiber near aggregating Asian oyster drill snails during egg-laying is an attempt to control the propagation of the invasive species. Unfortunately, the fibers do not last and are expensive. Jennifer Ruesink’s work prior to 2005 showed that it was better to remove eggs than adult drills to deplete the population. Catching adults just before egg-laying accomplishes both goals, but is a very time consuming and labor intensive process.

Dungeness crab do not prey on oyster drills, but green crab gobble them up with alacrity in the laboratory tanks. “The only problem is that green crabs are even more harmful to oysters and the habitat than oyster drills,” Sylvester explains.

“Willapa Bay is an amazing, huge bio-reactor. When its waters heat up, the biology really happens. It is an ideal environment to study oyster drill snails and hopefully find a solution that can be used world-wide,” Sylvester says.

Just as the snails attack and kill an oyster, so slowly, inexorably Sylvester and others are attacking them in the lab. “It took 6,000 tries before scientists found something that could control lamprey eels in the Great Lakes. I’m not sure I’ll live long enough to find something to control oyster drills, but someone will,” Sylvester concludes.