Tracking a voracious invasive predator

Posted 12/8/15

Washington Sea Grant (WSG) is responding to a possible threat from an invasive crustacean, with monitoring sites across Puget Sound, including in Jefferson County.

The European green crab, a small …

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Tracking a voracious invasive predator


Washington Sea Grant (WSG) is responding to a possible threat from an invasive crustacean, with monitoring sites across Puget Sound, including in Jefferson County.

The European green crab, a small but highly efficient and adaptable predator, has colonized waters and threatened native shellfish from South Africa to Australia to the Pacific and Atlantic coasts. First found on the West Coast in San Francisco Bay in 1989, the green crab has been blamed for the collapse of the softshell clam industry in Maine, according to a press release. The European green crab has appeared in other West Coast bays, including Coos Bay in Oregon, and Willapa Bay in Washington, and in 2012, the first known colony in the inland Salish Sea was discovered near Victoria, British Columbia.

This discovery sounded an alarm for Puget Sound’s shellfish beds, and Washington Sea Grant responded with a new, carefully targeted monitoring effort to catch infestations before they become problems.

“Our goal is to find a green crab population as early as possible to increase our chances of controlling its spread,” said Jeff Adams, WSG marine water quality specialist and project manager.

This summer, working with the Washington Department of Fish and Wildlife and other partners, WSG deployed the first trained volunteers in its proactive European Green Crab Volunteer Monitoring Program.

One of the monitoring sites is Kala Lagoon, near Kala Point along Port Townsend Bay, said Annie Hillier of WSG. Many beaches around Port Townsend, Port Hadlock and Dabob Bay also have been identified as high suitability sites for the invasive species, Hillier said, so the hope is to recruit volunteers to monitor these areas.

University of Washington scientists identify the beaches and bays where green crabs would most likely thrive, and volunteers set traps provided by the monitoring program along these shores at regular intervals. The volunteers then collect the traps and assess the catches. They also systematically search the shoreline for molted green crab shells.

This summer, WSG trained 49 volunteers in the protocols for the new program and gave them hands-on experience in citizen-science data collection. The volunteers deployed the first test traps in July, and have continued monitoring since then. Whether or not the volunteer monitors find invasive crabs, they tally the other animals that are drawn to their traps.

“Volunteers can contribute significantly to our overall understanding of common native species through this program,” said Adams. They record the numbers, sex ratios and sizes of all the animals trapped, valuable data that’s scarce even for common species such as shore crabs and sculpin. Adams recalls one trap, baited with mackerel at Whidbey Island’s Deer Lagoon, that came up teeming with 500 shore crabs “packed shoulder to shoulder.”

The volunteers also help educate the public. The sight of monitors on the tidal flats, baiting and gathering their traps, draws questions from beach walkers and other onlookers, who then learn more about the threat of green crabs and other invasive species. They may even become informal monitors themselves.

“You don’t have to be a trained monitor to help,” said Adams. “We also want anyone who enjoys our beaches to learn about the invasive green crab and know how to report it. We encourage everyone to get involved, learn what a green crab looks like and report what they find.”

For more information, visit Washington Sea Grant’s website, To report a European green crab finding, contact Jeff Adams at