Green Crab Monitoring

Green crabs are an invasive species that threaten clam populations, eelgrass beds, and local marshes.  To find out more about these crabs, KELT purchased green crab traps with the help of a grant from the Maine Outdoor Heritage Fund in 2014. Since then, these traps have helped to gather information about crab populations in our region.  KELT used them to work with students at Bath Middle School to trap green crabs and document information about their populations each fall.

What's a Green Crab?

• Green Crabs have 5 spines on each side of their eyes

• Their carapace (shell) is roughly pentagon shaped

• The crabs can be green, brown or red

• Green crabs rarely grow larger than 3 1/4 inches

• The size measured is the width of the crab at the widest part of its carapace – from the tip of one spine to the other

• Females have a rounded “Beehive” shape on underside, while males have a pointed “obelisk” shape

Green Crab Trap Types Used in the Kennebec Estuary

• Eel Trap

• Minnow Trap

• Modified Lobster Trap

• Shrimp Trap

• Acer Crab Trap

Kennebec Estuary Green Crabs in the News

Bath Middle School Green Crab Population Study

• ‘Bath Students, KELT, Team Up’ in The Times Record 10.28.2013

• ‘Coastal Classroom: Beachcombing Bath Students Learn About Invasive Crabs’ in The Forecaster, by Alex Lear 10.29.2013

• ‘Bath Students Obtain ‘Real’ Learning: Conducting Green Crab Study’ in The Times Record 10.27.2014

Georgetown

• ‘Clam Farming Eyed as Possible Solution to Green Crab Invasion’ in The Times Record 12.18.2013

• ‘Clam Class: KELT event teaches explorers of all ages’ in The Times Record 7.18.2014

• ‘Heal Eddy Restoration Project in Georgetown: Seeding clams — early results point to late fall as best time’ in The Times Record 10.15.2014

Woolwich

• ‘Woolwich Clammers Prepare to Fight Back’ in the Wiscasset Newspaper 1.8.2014

• ‘Woolwich Students Help Out: Clam Seed Study’ in The Times Record 5.27.2014

Arrowsic

• ‘Keeping Count in Arrowsic: For now, green crabs cause little worry’ in The Times Record 6.26.2015

• ‘Consistent Numbers for Arrowsic Green Crabs: Latest data based on recent one-day trapping assessment’ in The Times Record 7.10.2015

Green Crab Resources

• Maine DMR – Green Crab Webpage

• Maine DMR – Green Crab 1 Day Trapping Survey Report

• Maine Green Crab Summit – information and presentations from the December, 2013 Green Crab Summit

Bath Middle School Trapping

Bath Middle School 7th grade students and teachers spend their fall exploring information about local fisheries.  This exploration includes learning about invasive green crabs and trapping them to find out information about their population and how it changes over time. 

The students carry out a simple population study to try to estimate the number of crabs in the area where they are trapping and find out information about those crabs.  Traps are set for 12 to 24 hours.  When the traps are pulled, students count the number of crabs in each trap and record the size, color, and sex of each crab. To estimate population, they paint a dot of nail polish on the shell of each crab.  The crabs are released, and the traps are set for another 24 hours. When they are hauled, the same information is collected for each crab caught, and the number of crabs with painted shells are recorded. Based on the number of crabs caught on both days and the number of crabs caught on only the 1st or the 2nd day, the students can estimate the total population of crabs in the area.

Thank You To Our Green Crab Project Sponsors!

Maine Outdoor Heritage Fund

The Margaret E. Burnham Charitable Trust