Ornate little snails hanging out in the Skokomish estuary have sneaky intentions with Pacific oysters.
Much like humans who love slurping oysters, so does the invasive Japanese oyster drill, a 1.5-inch brown snail that attaches itself to an oyster, drills a toothpick-size hole though the shell with its sharp tongue-like structure, then secretes a digestive enzyme into the oyster to liquefy and eat it.
The Skokomish Tribe is undertaking control efforts on drills, evaluating distribution and the effects on oyster populations. The tribe’s current focus is a drill hot spot around the central freshwater drainage of the Skokomish estuary.
The predatory snails came from Japan, hitching a ride on Pacific oysters that were imported in the early 20th century. Studies have shown a preference for Pacific oysters, however, drills have been observed to also be detrimental to native Olympia oysters during restoration efforts in some locations. In the Skokomish estuary area, drills are found almost entirely around Pacific oysters.
Since March, the tribe has been setting up 50-foot-long transects during daytime low tides to sort through oysters and remove any drill snails present. The tribe also removes drill snail eggs, clusters of tiny yellow capsules attached to oyster shells.
“We’re collecting data on distribution and monitoring behavior such as clustering, feeding and egg-laying,” said Max Wiecek, the tribe’s aquatic invasive species coordinator. “We’re also trying to understand habitat types that the oyster drills prefer, like freshwater drainage channels at lower tidal elevations—where we find more—or oyster clusters at slightly higher elevations—where we find less—and why these distributions vary so greatly.”
During these surveys, oyster drills were found not only on oysters but also clams, barnacle clusters and woody debris. The only feasible way known to eradicate them is by hand picking, Wiecek said. After drills are picked and counted, the shells and their eggs are weighed to get a metric for how much is being pulled off the oyster beds.
The tribe first started oyster drill control efforts in 2014, when 72 cinder blocks were placed in the estuary for the drills to latch onto with the hope of lessening impacts on existing oyster beds. The tribe spent the next two years pulling more than 100 pounds of oyster drills from the cinder blocks as well as seeded Pacific oyster clutch bags that were temporarily in the area.
Preliminary data from the new transect surveys will help the tribe determine where to focus further removal efforts and how much risk there is for the tribe’s oyster beds, Wiecek said. The tribe also will pick up the cinder block work again next year with the daytime low tides.
“We have reason to believe that oyster drills should be removed to give oysters more breathing room in the face of other stressors,” Wiecek said.
Top photo: Max Wiecek, Skokomish Tribe aquatic invasive species coordinator, pulls an oyster drill off an oyster by its ornate, spiral shell. Story and photos: Tiffany Royal
