European green crab are growing in numbers in Grays Harbor, and volunteers, state agencies, tribes and shellfish growers are working together to control the destructive invaders.
Twin Harbors Waterkeeper Lee First is one of those volunteers. In April, a trap was set on the south side of Grays Harbor, near the old Saginaw Mill site, to see if any green crab could be found.
European green crab are on the state Department of Fish and Wildlife’s list of “aquatic invasive species of greatest concern.”
“The green crab is often called one of the most damaging invasive species worldwide,” said Emily Grason, Washington Sea Grant crab team lead. “As we’re seeing numbers on the rise in Washington there is concern because of the damage that’s been caused where it’s been established outside its range.”
The crab are so destructive because “everything is on the table for green crab in terms of diet,” said Grason. They will feed on small fish, including salmon smolt, juvenile razor clams, juvenile oysters, native crab species, “anything they can sort of break apart, including vegetarian diet of seaweed or eel grass.”
Eel grass is “a foundation species ecologically,” said Grason. “Salmon rely on it, juvenile Dungeness crab and a host of other organisms are really reliant on eel grass at least in certain times of their development.” It also has importance for carbon storage.
First got into the program when she was speaking to a shellfish grower; shellfish growers are among those with the most to lose if the green crab population continues to grow.
“If green crab become really abundant and that’s an item they have access to, absolutely commercial and wild bivalve shellfish could be endangered,” said Grason. “Recreational and tribal fishermen really rely on them for sustenance and enjoyment.”
Monitoring
The crab team partners with the state Department of Fish and Wildlife, the Quinault and Shoalwater Bay tribes, shellfish producers and volunteers to set traps. They also can use the public’s help in identifying areas where green crab are found.
Over the last year, a few sites have been monitored locally, including the new one in Grays Harbor, several in Ocean Shores and some in the South Bay area. Alex Stote, coastal specialist with the crab team, has started up a handful of new sites in the area.
In its 2020 update, the crab team said five new sentinel sites — where trapping occurs once a month in the same location April-September — were established, and the team completed multi-day assessments at 21 locations throughout Willapa Bay and Grays Harbor in partnership with Fish and Wildlife.
The payoff was a total of 915 trap sets and 1,762 green crabs removed in Willapa Bay, Grays Harbor and Makah Bay from August through October 2020. Additional trapping by the Makah Tribe and Pacific County Weed Management had removed nearly 1,500 crabs during the year.
“Based on what we’ve seen over the past three or four years they are more abundant in Grays Harbor than they have been since they were first detected in the late 1990s, but that said they are not as abundant as we think they can get,” said Grason. “We haven’t seen the worst of it yet. We’re really never going to have a better time to intervene than right now.”
According to the crab team 2020 report, the average catch rate was greatest at Ocean Shores — an average of roughly 562 crabs caught for every 100 traps set. Among Willapa Bay sites, Stackpole and Tokeland had the most crabs — an average of 294 and 244 crabs per 100 traps, respectively.
Setting the trap
Stote said sentinel traps are set in tidally influenced salt marsh channels with little fresh water input. More intensive trapping efforts, called assessment trapping, are where trapping is done over the course of several days in one area, but that area isn’t monitored monthly like the sentinel sites. Traps cover a wider range of habitats in the assessment trapping.
Traps are baited with mackerel, pinned to the channel floor, and the timing is set around the tides.
“We’ll set the trap right, essentially, when the tide is coming in,” said Stote. The channel is flooded by the tide, then checked as soon as the trap is exposed by the falling tide. “We’re trying to limit bycatch mortality,” she said, as other native species can also find their way into the traps.
“We only found fish, we didn’t have any green crab or any other kind of crab in our trap,” in her first trap-set in April, said First. The traps will be set for another test again May 18.
How to help
First spends a lot of time kayaking around Grays Harbor and keeps her eyes open for green crab molts, the crabs’ discarded shells.
“I was out in Elk River a couple days ago and found two European green crab molts,” said First.
As part of its monitoring efforts, the crab team has a spot on its website, wsg.washington.edu/crabteam, to report sightings of live green crab and molts. This is the best way for the public to help with the effort to track and eventually remove green crab.
“People just need to take a photograph and leave the crab where it is, which sounds a bit weird, but currently we want to make sure we’re not accidentally disposing of native crab, which can help in the management of green crab,” said Grason. Directions for reporting are on the crab team’s website.
That website also has photographs and detailed physical descriptions of the green crab. Unfortunately, despite its name, its color is not a distinguishing feature as the shell color can vary widely. There are native crab species that are green as well. The key distinguishing feature of this species are the five spines found to the outside of the eye on the shell. This number of spines is different from any other crab you are likely to see on the beach in our area.
Removal
There’s no easy way to get green crab out of the environment.
“The desire is to develop a cohesive and collaborative plan that will rely on the efforts of a lot of groups,” said Grason. “The best method we have now is trapping.” There is a lot of effort to hone in on the perfect gear, the perfect trap and bait, but “unfortunately there is no silver bullet when it comes to trapping green crab. It takes a lot of work and a lot of traps to repeatedly pull more and more out. Consistent, repeated effort is needed to drawn down the population.”
