Watching out for green crabs

A female European green crab with her egg mass. Photo by Linda Shaw, NOAA Fisheries

Here's interesting news about an effort to detect the insidious European green crab possibly making its way north into Southeast Alaska waters. Pray this thing never arrives!

NOAA Fisheries

May 1, 2009

Network sets traps to find any green crabs in Alaska

With spring weather, experts from natural resource agencies, professors, teachers, students and citizens in Alaska are increasing their vigilance for oceanic aliens: European green crabs.

Ketchikan resident Gary Freitag will board a plane within the next couple weeks to ride to Shelter Cover, on Dall Island on the outer coastline of Southeast Alaska to set small crab traps where green crabs are likely to make their first appearance in Alaska.

Freitag works for Alaska Sea Grant which is funded by NOAA and the University of Alaska. He is also an adjunct professor at the University of Alaska Fairbanks in Ketchikan. The cooperative nature of his funding echoes what can be seen across the state: Many people from scientists to fishermen to citizens to students, with federal to state to private affiliations have their eyes open for the first sign of green crabs.

“Trained monitors set small crab traps during low tides and check after 24 hours have passed,” explained Linda Shaw, invasive species expert with NOAA Fisheries in Juneau. “Most start in May and trap through into September. But in Ketchikan, Gary Freitag is also trapping in the winter.”

Green crabs top out at about 10 centimeters (4 inches) across. They displace native species with their voracious eating and breeding habits: clams, oyster, mussels, marine worms and other crabs fall prey. Green crabs also devour herring, salmon bones, or canned cat food, which are most commonly used to bait the traps.

The crabs appear to be moving northward on the currents. Scientists have found them in substantial numbers on the outside coastline of Vancouver Island in British Columbia and speculate that they may have already spread northward to the Queen Charlotte Islands. Vigilant monitors have not yet found any green crabs in Alaska, but the estuaries and sheltered coves of Southeast Alaska are the most likely first sighting points.

Green crabs can also hitch a ride in ballast water of ships. So in Dutch Harbor, Homer, Kodiak, Tatitlek, Whittier, Valdez, Cordova and Chenega in western and south-central Alaska as well as Glacier Bay, Sitka, Juneau and Ketchikan in southeast Alaska, dedicated individuals are regularly wading into the shallows to check their traps.

Green crabs invaded Cape Cod nearly two centuries ago. They arrived somewhere between New Jersey and Massachusetts, probably on rock ballast or in the hulls of European ships. They have been spreading in North America since. In San Francisco, California, a breeding population was discovered in 1989. Green crabs were found off Oregon in 1997, off Washington in 1998 and off British Columbia in 1999. Their population has boomed in British Columbia.

The Smithsonian Environmental Research Center started the first dedicated program monitoring for green crabs in Alaska in 2000. The Prince William Sound Regional Citizens’ Advisory Council started monitoring in Prince William Sound in 2005. In 2007, NOAA Fisheries sponsored a training workshop in cooperation with the Prince William Sound Regional Citizens’ Advisory Council and Alaska Department of Fish and Game.

NOAA Fisheries recruited and trained monitors in Ketchikan, Gustavus and Sitka. The Southeast Alaska monitors completed their first season of trapping in 2008. In all, the network of formally trained crab-trappers has expanded to about a dozen people in a dozen locations statewide. But they are not alone: many others also have their eyes open for green crabs.

Anyone who suspects they may have seen or caught a green crab should call the State of Alaska Department of Fish and Game at 1-877-INVASIV (1-877-468-2748). For more details on green crabs, click here.