Home » Blog posts » Green crabs in Hood Canal raise questions about invasion; further response is coming

At Nick's Lagoon on Hood Canal, Bev Howald, right, measures a hairy shore crab, while Victoria Poage checks the sex of another, and Brian Gregory records the data. No European green crabs were caught in their traps this week, but last month this team caught the first green crab ever found in Hood Canal. Photo: Christopher Dunagan

Green crabs in Hood Canal raise questions about invasion; further response is coming

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For the past six years, a volunteer crew has been diligently visiting Nick’s Lagoon near Seabeck on Hood Canal, checking the waters for the destructive European green crab.

The three citizen scientists have caught and released lots of native crabs — including thousands of hairy shore crabs. But, until May of this year, they never saw even one invasive green crab, known for its potential disruption of shellfish beds and destruction of native habitat.

Sites in Puget Sound where monthly trapping takes place to find European green crabs. Yellow marks locations where green crabs have been found. Click on map to adjust scale. // Map: Washington Sea Grant Crab Team

The discovery of a green crab in Central Hood Canal was fairly shocking for those involved. Despite an extensive trapping effort, green crabs had never been spotted in Central or South Puget Sound, and this green crab in Hood Canal was more than 30 miles by water to the nearest confirmed sighting.

With Nick’s Lagoon located less than five miles from my house, I decided to drive over there on Tuesday to observe the monthly trapping effort and report on the latest information about green crabs in Puget Sound.

Bev Howald of Poulsbo, one of the volunteers, said it took the team a moment to realize that they were making history in May when they pulled the crab trap from Nick’s Lagoon and emptied its contents into a small tub.

“The first thing I said was that this is the biggest crab we have ever caught,” Bev told me.

Fellow volunteer Brian Gregory’s reaction: “This can’t be good.”

Bev recalled how the “feisty” crab stood out from all other crabs caught before in Nick’s Lagoon, which is owned by Kitsap County. She was hoping that the team’s identification of a green crab had been a mistake. But their training had prepared them for this finding. It was the first catch of a green crab south of Marrowstone Island, as confirmed by state biologists.

The response to the discovery was rapid, with biologists from the Washington Department of Fish and Wildlife descending on Hood Canal and placing dozens of traps at 10 locations deemed suitable for green crabs, from Guillemot Cove to Anderson Landing. Out of 376 “trap sets” — each lasting one day — 10 more green crabs were caught at Nick’s Lagoon plus one at nearby Misery Point Lagoon and another at Big Beef Creek estuary to the north.

The following week, June 1-2, 22 traps were set for a day at Nick’s Lagoon, catching one more green crab.

This week’s trapping effort by the three volunteers yielded a normal number of hairy shore crabs, but no green crabs in the six traps placed in the water.

A tub of hairy shore crabs, but no green crabs, were caught in traps this week in Nick’s Lagoon.
Photo: Christopher Dunagan

“We can hope that we trapped out the population,” Brian said, although he knows that some green crabs may still be out there.

The green crabs in Nick’s Lagoon no doubt arrived in their larval form, drifting with tidal currents, probably for many miles, after hatching at one or more unknown locations. The crabs ranged from 34 to 70 millimeters, or 1.3 to 2.5 inches, across their shells. Based on their size, none of the crabs was more than two years old.

So far, there is no sign of a breeding population in Nick’s Lagoon, according to Emily Grason, a marine ecologist who coordinates the green crab program for Washington Sea Grant. Whether the population expands or dies out may well depend on environmental conditions as well as the number of surviving crabs. To maintain or expand their population, remaining males and females must find each other and mate successfully.

Discovering a green crab in Central Hood Canal marks a potential expansion of the population within Puget Sound, where an ongoing trapping effort caught the first green crab on San Juan Island in August 2016 (Water Ways). Since then, green crabs have been found in more than a dozen bays and harbors in Northern Puget Sound.

Suitable habitat for green crabs appears to be abundant in Central and South Puget Sound as well as Hood Canal, according to Emily. She says she can’t predict where they will be found next, but she is no longer surprised by what they do.

As a method for early detection, volunteers with Washington Sea Grant’s Crab Team are deploying traps at 57 sites throughout the greater Puget Sound region, including four sites in Hood Canal: Zelatched Point on Dabob Bay, the mouth of the Duckabush River, Musqueti Point between Dewatto and Tahuya, and Nick’s Lagoon near Seabeck. (Click on the map on this page for a closer view.)

The first green crab found in Hood Canal was caught in a trap May 17 at Nick’s Lagoon. // Photo: Washington Sea Grant

The standard procedure used by volunteers is to set out the traps each month from April to September. The Nick’s Lagoon Squadron, as the three call themselves, has not missed a month of sampling since its inception in 2016. Victoria Poage of Bremerton is the third member, in addition to Bev Howald and Brian Gregory.

All the trappers use mackerel as bait to attract the crabs, allowing for a consistent protocol. Every creature caught in the traps gets counted, including every type of crab, fish, snail and other species. Each crab in the trap is turned upside-down to check on its sex. When there are lots of crabs of one species, such as hairy shore crabs, a sample of 10 males and 10 females are measured for size.

The spread of green crabs in Hood Canal comes at a time when Fish and Wildlife officials are developing a new statewide plan of action for these invasive species, thanks to increased funding from the Washington Legislature. Planning involves multiple agencies with various expertise, including tribal biologists. Washington Sea Grant manages the Crab Team with its early-detection network while providing scientific and technical advice.

In January, Gov. Jay Inslee issued an emergency proclamation to address the exponential increase in the green crab population in light of the Lummi sea pond, where about 70,000 green crabs were caught last year, and along Washington’s Pacific Coast, where nearly 16,000 green crabs were caught during the year.

Allen Pleus, aquatic invasive species coordinator for WDFW, said further work in Hood Canal will be planned as the agency works out statewide priorities for green crab. “There are good reasons to go back into Hood Canal and do more trapping,” he told me, adding that the actual work could be coordinated with local entities interested in conducting the trapping.

New funding from the Legislature allowed for the green crab budget to be increased from $2.3 million to $3.6 million during the fiscal year that ended yesterday, and a new allocation of $7.25 million will cover the next year of work starting today.

“Washington’s European green crab management efforts have really ramped up this year with Governor Inslee issuing a statewide emergency proclamation and the Legislature authorizing new emergency funding resources,” Pleus said in a news release. “This detection in Hood Canal by community scientists and the rapid response of numerous traps and other equipment by WDFW exemplifies the collaborative approach we are taking to control these invasive crabs and prevent them from harming environmental, economic, and cultural resources.”

Besides increasing trapping efforts at locations where the crab populations have exploded, the extra money can be used to support a “strike team” to look at sites other than those monitored monthly by Crab Team volunteers, Allen said. The strike team had been working in Puget Sound last year until team members were called on to boost response efforts at the Lummi sea pond. New staffers are being hired and trained to cover these and other priorities, he said, and all hands should be on deck by the end of July.

“I feel great about this amount of money,” Allen noted, even though supply-chain issues have slowed down the acquisition of new equipment. “We will find out if the money is sufficient by the end of the fiscal year.”

Funding also has been increased for public outreach to help people understand the emergency situation involving the green crab and other aquatic invasive species, such as those that may get released from home aquariums, said Allen, who serves as incident commander for the green crab emergency.

Because of the difficulty of identifying crabs by species, untrained individuals are asked to take pictures of any suspected green crab and report it to authorities rather than removing the crab, which may turn out to be a native species.

Anyone who would like to volunteer with Sea Grant’s Crab Team can sign up to receive the group’s newsletter and learn to identify the crabs with flashcards and other tools on the website. Formal training sessions for volunteer trappers who would like to work in the field will be scheduled during the coming winter and next spring.

Meanwhile, researchers are continuing genetic investigations, including studies of DNA taken from captured crabs. One goal is to identify the origins and dispersal patterns of green crabs as their population shifts throughout the Northwest.

Other genetic studies are focused on environmental DNA, or eDNA, used to determine if green crabs or their larvae may be present in an area. The process involves testing water samples for trace amounts of genetic material released by the organisms. The eDNA tests can be used in conjunction with trapping to help with the early detection of green crabs and calculate a relative abundance at a given location.

In Nick’s Lagoon and other areas in Hood Canal, researchers collected water samples for eDNA testing at sites where trapping was done. Abby Keller with the University of Washington’s School of Marine and Environmental Affairs has been leading studies to understand the uses and benefits of eDNA techniques, which may be especially valuable in locations with low densities of crabs and where deploying traps would be difficult. Check out the technical article published Feb. 6 in the journal Ecological Applications or read Michelle Ma’s story about the work in UW News.

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