A single green crab invader has been found, the first in Puget Sound

A European green crab, one of the most dreaded invasive species in the world, has finally arrived in Puget Sound.

Caught in a crab trap on San Juan Island were these animals — including the first European green crab ever found in Puget Sound. Photo: Photo Craig Staude, courtesy of Washington Sea Grant
Caught in a crab trap on San Juan Island were these fish, along with the first European green crab ever found in Puget Sound.
Photo: Craig Staude, courtesy of Washington Sea Grant

A single adult green crab was caught in a trap deployed on San Juan Island by a team of volunteers involved in a regionwide effort to locate the invasive crabs before they become an established population.

Until now, green crabs have never been found in Puget Sound, although they have managed to establish breeding populations along the West Coast — including Willapa Bay and Grays Harbor in Washington and the western side of Vancouver Island in British Columbia.

Coincidentally, I recently completed a writing project on invasive species for the Encyclopedia of Puget Sound, including a story about green crabs and the volunteer monitoring program.

Here’s what I wrote: “Puget Sound has so far avoided an invasion of European green crabs — at least none have been found — but the threat could be just around the corner….

“Green crabs are but one of the invasive species threatening Washington state, but they are getting special attention because of fears they could seriously affect the economy and ecosystem of Puget Sound. Besides devouring young native crabs and shellfish, they compete for food with a variety of species, including fish and birds.”

Along the beach, careful observers can often find crab molts. The green crab, upper left, can be distinguished by the points on its carapace. Photo: Jeff Adams, Washington Sea Grant
Along the beach, careful observers may find weathered crab molts of all sizes. The green crab, upper left, can be distinguished by the five points on each side of the carapace. (Click to enlarge.)
Photo: Jeff Adams, Washington Sea Grant

In Canada, one breeding population has been identified in Sooke Inlet near the southernmost tip of Vancouver Island. That’s about 40 miles away from Westcott Bay, where Puget Sound’s first green crab was found on Tuesday.

It is likely that the crab traveled to San Juan Island in its early free-swimming larval form by drifting with the currents, said Jeff Adams, a marine ecologist for Washington Sea Grant who manages the Crab Team of volunteers. This crab likely settled down in suitable habitat and located enough food to grow into an adult. Based on the crab’s size, it probably arrived last year, Jeff told me.

European green crab Photo: Gregory C. Jensen, UW
European green crab // Photo: Gregory Jensen, UW

Finding a green crab in Puget Sound is alarming, Jeff said, but it is a good sign that the first crab was found by the volunteer monitors. That suggests that the trapping program is working. If this first crab turns out to be a single individual without a mate, then the threat would die out, at least for now.

The concern is that if one crab can survive in Puget Sound, then others may also be lurking around, increasing the chance of male-female pairing. The next step is to conduct a more extensive trapping effort in the area where the first green crab was found, then branch out to other suitable habitats in the San Juan Islands, Jeff said. The expanded effort is planned for the week of Sept. 11 and will include a search for molts — the shells left behind when crabs outgrow their exoskeletons and enter a new stage of growth.

Green crab
Green crab

Researchers and others who work with invasive species quickly recovered from their initial surprise at finding a green crab in Puget Sound, then got down to business in planning how to survey for crabs and manage their potential impacts.

Allen Pleus, coordinator of the Aquatic Invasive Species Program at the Washington Department of Fish and Wildlife, told me several weeks ago that if green crabs show up in Puget Sound, one idea would be to conduct an extensive trapping program to eradicate or at least reduce their population. First, however, the extent of the infestation must be identified. I expect that more extensive trapping will be planned next spring and summer to look for offspring from any successful mating in the San Juan Islands.

This video shows a green crab found in Willapa Bay on the Washington Coast.

Typically, green crabs are found in marshy areas, which are habitats extensively used by our native hairy shore crab. But Jeff tells me that some populations of green crabs seem to be expanding their habitat into more exposed rocky areas.

With roughly 400 suitable sites for the crabs in Puget Sound, invasive species experts are calling for everyone who visits a beach to look for green crabs and their molts. One can learn to identify green crabs from the Washington Sea Grant website. The volunteer trapping program is funded by the Environmental Protection Agency with a grant to Fish and Wildlife.

A public discussion about green crabs and how people can help protect Puget Sound from an invasion is scheduled for Sept. 13 at Friday Harbor Laboratories on San Juan Island. See Crab Team Public Presentation.

10 thoughts on “A single green crab invader has been found, the first in Puget Sound

  1. Are they edible ? If so, why not place a year-round open season with no size or quantity limits on them. Otherwise if non-edible place a bounty on them.

      1. Thanks Laura, great read & great ideas. I invite ALL concerned readers and ‘crab enthusiasts’ to read Laura’s offering.

  2. are they edible? if so, let everyone know ( and make sure no game wardens will hassle anyone for taking every one they find . . . . . )

  3. Before we get carried away with hunting green crabs and eating them, let’s remember that one — just one — green crab has been found so far in Puget Sound. The Washington Department of Fish and Wildlife has a plan to search for more. Officials would like people to be on the lookout for them. If you find a molt (discarded shell) of a green crab, take it for identification. If you find what you think is a live green crab, take its picture, note the location and contact authorities. I wouldn’t assume the risk of taking a live crab out of season.

  4. On the TV news they said not to touch them. Why? If nothing else, why wouldn’t a person smash it with a rock? Are they doing anything with them in Willapa Bay?

    1. Great questions…
      – don’t touch = just means take pictures and leave the crab. If it actually is a green crab, WDFW and the WSG Crab Team will respond with a period of intensive trapping at the site to capture the crab you found and get an idea of how many are there. … They also pinch!
      – smash it on a rock = If it were truly a green crab, but it’s better to let an expert make that call. So far, 100% of the photo reports we’ve received have been native species (thankfully).
      – Willapa = There are not currently control efforts in Willapa Bay and Grays Harbor, though there is some monitoring annually. Crab Team staff recently trapped heavily in a couple ares of Willapa and caught only 4 green crabs. There have been a few crabs there each year, but the numbers appear low. Conversely, on Vancouver Island, the crabs are very successfully reproducing and number are growing at different populations. Willapa and Grays may receive more attention in the future.

  5. Excellent questions about harvesting. Though edible, they aren’t any bigger than your fist, and when we’re spoiled with Dungeness, it’s not the most appealing crab meal. More importantly, there are very very few in the Salish Sea right now, and the goal is to keep the populations from ever getting large enough to harvest and to prevent the ecological/economical impacts that could come with that many omnivorous crabs.

    Some invasive or potentially invasive species are classified as “prohibited” and are illegal to possess. Part of the reason is to prevent the accidental (or intentional) spread of a species to new habitats. There are examples of species that have gotten out of control and for which harvest is now allowed. Crayfish is one. Harvest of invasive crayfish is now allowed, but harvesters must be able to tell the difference between native and invasive crayfish and must kill the invasive crayfish when they catch them (before leaving the water body where they were collected). Again, the goal of an early detection program like WSG’s Crab Team is to prevent getting to that point and to avoid the impacts that the species can have on our native shellfish, other species, and shoreline habitats.

    A few other points…
    – The only crabs that are legal to collect in the state of Washington (without a scientific collection permit) are Dungeness and red rock, and Dungeness and red rock can only be taken with the appropriate recreational harvest permits, during the specified season and within size and number limits.
    – European green crab are a prohibited species which sort of makes them doubly illegal to possess.
    – Volunteers in the Crab Team program
    received specific training on identification and have a special permit to take green crab should they trap or find them.
    – Molts (shed skins that can be found on the beach) can be safely and legally collected. Please do and and send a picture to crabteam@uw.edu
    – A picture is enough for experts to confirm something is a green crab. If confirmed, the precise location would be identified, then intensively trapped to catch that crab and others may be in the area.
    – Crab Team and WDFW appreciates and really wants to encourage reports of crabs that fit the description of a green crab. Because the chances of finding a green crab are very small, releasing a crab after a photograph will allow us to avoid possible harm to native species. To date, the reports we’ve received have all been of native species. Please keep them coming though! crabteam@uw.edu

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