A boat captain leading a group of high school students caught a giant blue crab in the Chesapeake Bay.

The male crab appeared to measure between 16 and 18 inches claw-to-claw, although an exact measurement was not taken. Officials measured the width of the shell, a common way to measure crabs, and found it was eight inches across. That makes it one of the larger crabs found in the bay. Officials said they believe the crab is between 4 and 5 years old.

Ian Robbins, the captain leading the high school students on an educational trip, caught the crab Sept. 27 in the bay near the Susquehanna River in the Harford County area. This week, the Chesapeake Bay Foundation posted photos on social media of the giant crab.

Tom Zolper, assistant media director at the Chesapeake Bay Foundation, said Thursday the group on the boat was not trying to crab but “just trying to see what was on the bottom” of the bay. He said the area where the boat was at the time, known as Susquehanna Flats, is considered to be more freshwater than saltwater.

The area is known for having a lot of sea grass. Zolper said the big crab could have been hiding for some time in the grasses, helping it evade capture.

“The fact that they’re not caught that often or appear that often doesn’t mean they’re rare,” Zolper said of the giant crab. “It just could be where the watermen are searching for crabs.”

This spring, authorities had estimated there were more than 550 million blue crabs in the bay — a major increase over the previous year and one of the largest populations in two decades. Blue crabs are known as the “beautiful swimmer” and are perhaps the best known wildlife species in the bay.

What became of the giant crustacean? The group put the giant crab back in the bay.