Station 3: About Crabs

The animal most people associate with the Chesapeake Bay is the blue crab. Blue crabs are well suited to the ever-changing salinity of the estuary, and can tolerate water ranging from salt to nearly fresh.

Because of their abundance and popularity as a food, people have been able to make their living from catching crabs. One of methods the students will use, the collapsible hand trap, is a popular method used by many crabbers. People also catch crabs using just a line and bait. Students will also try this method. Crabs most often act as predators, eating clams, fish and other soft-crabs, but are also scavengers and will be attracted to the bait in the crab trap.

The abundance of crabs varies seasonally. They begin to enter the rivers and creeks in April and continue to increase in number throughout the summer. In the fall they gradually go back into the deeper water of the Bay and stay there over the winter. SERC keeps a record of the numbers of crabs caught by school groups so that each group will be able to relate their catch to seasonal fluctuations.

Objectives

At this station, students will:

• Catch crabs using the collapsible trap and the string and bait technique.
• Name the external parts of the blue crab including the shell, abdomen, mouth, eye stalk, claw, swim paddles, and walking legs.
• Identify the sex of a crab by examining the abdomen.
• Measure different crab sizes to see how much crab size increases after molts.
• Study crab behavior.
• Record the number of crabs caught, the sex, and the size.

Science standards

Maryland Content Standards
About Crabs Science Indicators:
1.0 Skills & Processes: 1.5.1, 1.5.5, 1.5.6, 1.5.7, 1.5.11
3.0 Life Science: 3.5.2, 3.5.5, 3.5.6, 3.5.12
6.0 Environmental Science: 6.5.2, 6.5.3

Virginia Standards of Learning
About Crabs Science Indicators
Scientific Investigation, Reason & Logic: 4.1, 5.1
Living Systems: 4.5
Interrelationships in Earth/Space Systems: 5.6
Resources: 4.8