Young Green Crabs Are Just As Destructive As Adults, WSU Says

Researchers at Washington State University say juvenile European green crabs can do as much damage as adults to shellfish and native sea plants.  These new findings call into question current methods to eradicate the invasive pest.

For years, green crabs have been a massive threat to Washington’s shellfish industry as well as its native eelgrass, a plant vital to local seawater ecology.  Because of that, shellfish growers have been trapping green crabs in huge numbers, traditionally targeting adult crabs because they are easier to catch and remove.  More than 1.2 million were caught in Willapa Bay and Grays Harbor alone last year.  But this new study shows that current removal techniques may not be enough.

WSU scientists found that juvenile crabs can crack into immature shellfish, grown for humans to eat, just as easily as the larger-clawed adults, according to a paper recently published in NOAA Fishery Bulletin.

We Need To Start Thinking About Long-term Pest Management

“We looked at claw size, thinking that bigger crabs would feed on more prey,” said Laura Kraft, a WSU shellfish Extension specialist based in Long Beach, WA.  “But we found that even little crabs fed on almost the same proportion of juvenile Pacific oysters as bigger crabs.”

Kraft and her colleagues compared young crabs to fully mature crabs, with both given different food items such as Manila clams and Pacific oysters. They found that the juveniles were just as capable of feeding on the immature shellfish provided. The finding may require a shift in mindset for the green crab invasion.

“We need to start thinking about long-term pest management,” Kraft said. “I don’t think eradication is possible on the southwest Washington coast. If that’s the case, we need to look at how we use our limited resources to manage the impact of these invasive crabs.”

Kraft and other scientists have launched new studies that could aid that approach.

“We are just starting to get a better picture of the impact these crabs are having along the coast,” she said. “We know that they will impact commercial shellfish in different ways, so how do we best protect that industry?”

Kraft hopes to work with groups around Willapa Bay and Grays Harbor, which both have huge green crab populations and important shellfish industries, to figure out how to fight adult and juvenile crabs.

Click Here to read the results of WSU's research.

The state of Washington is the top producer of shellfish aquaculture in the country, with production estimated in excess of $200 million annually.

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