Bath Middle School Green Crab Population Study


Bath Middle School 7th graders started surveying green crab populations in Woolwich and Phippsburg in October of 2013.  Now, every fall, students trap crabs at Reid State Park, Robinhood Cove, and Fort Popham.

Population Surveying in Plots

This section of the project followed procedures outlined by the Vital Signs program, a statewide effort to document and address invasive species.  Information from the survey plots was recorded on the Vital Signs website.  The students set-up a 1 meter square plot in green crab habitat and counted the number of crabs in each plot.

Crab Population Information and Trap and Recapture Population Estimates

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.

Study Findings

We will be sharing more information about the information the Bath Middle School students found out during their green crab trapping projects soon!