Concerns grow over invasive crab species in Drayton Harbor

Evidence is growing that there is now an established population of invasive European green crabs in Drayton Harbor.

In August and early September, shells of European green crabs were discovered in Drayton Harbor for the first time. Reacting to this development, the Washington Department of Fish and Wildlife (WDFW) conducted a “rapid response” in Drayton Harbor in late September, quickly setting traps in areas of the harbor that could potentially be inhabited by green crabs.

The results were shocking. Seventeen live European green crabs were trapped by WDFW in just a few days, representing the highest number of green crabs trapped in such a short period of time from any one area along Washington’s inland shoreline.

“Finding this many invasive green crabs so quickly in one area raises a serious concern that there may be an established and reproducing population in Drayton Harbor,” said Allen Pleus, WDFW’s aquatic invasive species manager, in an October 8 news release.

The European green crab is a shore crab whose native distribution is in the northeast Atlantic Ocean and Baltic Sea, ranging along coasts from northern Africa to Norway and Iceland. The arrival of the green crab on America’s west coast by 1989 worried experts, because the species has the potential to significantly alter any ecosystem it invades.

The green crab could threaten Dungeness crab, oyster and clam fisheries in the Pacific Northwest. This is because the green crab feeds on many organisms, including clams, oysters, mussels, marine worms and small crustaceans. It can also prey on native juvenile crabs and shellfish. “It will eat anything that it can get its claws around,” said Emily Grason, a marine ecologist with Washington Sea Grant at the University of Washington.

According to Grason, the 17 live European green crabs were discovered by WDFW in areas of Drayton Harbor including California Creek and Dakota Creek, where the muddy habitat is ideal for the invasive species.

She said that the 17 crabs were relatively young and small in size. It is unclear whether the 17 crabs were washed into Drayton Harbor as larvae, or whether they were born in Drayton Harbor to adult crabs reproducing here. “Both scenarios are possible, and it’s hard to tell the difference between them,” said Grason. “The best we can do is make an educated guess based on what we know about the crab life cycle and the oceanography of Drayton Harbor itself.”

The initial response trapping by WDFW was conducted from September 25 through 27. On October 8 through 10, another three days and two nights of trapping took place in Drayton Harbor, representing a collaborative effort by WDFW and Washington Sea Grant. There are only a few weeks left in the trapping season, and during this time, the researchers will be working to determine the geographic extent of the European green crab population in the area.

“We’ve been collaborating with WDFW to set traps over a wider area, to establish the extent of the range of green crabs before the end of the trapping season,” said Grason. “As the weather turns, it becomes impractical to trap over the winter for green crabs. We have only a couple of weeks left where we’re likely to be able to trap efficiently.”

Over the winter, Grason said that discussions will need to take place regarding how best to direct limited resources towards managing the European green crab population. “The only current tool in the toolkit is trapping them,” she said. “It is a labor- and time-intensive tool but it’s the best we have at the moment. We need to figure out how to do that in an intelligent, informed way.”

Starting next spring, Grason said that “locally vested interests” such as shellfish growers, tribes, municipalities and citizen groups will also be needed to play a role in trapping efforts, if Drayton Harbor’s green crab population is to be successfully contained. “Our role is to provide information and interpret what’s going on to help strategize, but we don’t have manpower,” she said.

To get involved with Washington Sea Grant’s green crab monitoring program, visit wsg.washington.edu/crabteam for more information. Their “crab team” uses citizen science to achieve a much greater scale of monitoring than would otherwise be possible.