We found a female blue crab at the Jersey Shore which had a 2" brown mass near its tail end held on by a piece of shell. Were these the crabs eggs? If they were, when do they release the eggs? Or does she keep them with her until they hatch? Thank you.
Very likely this was an egg mass, also called a "sponge." The female crab carries the sponge until the eggs hatch, a period of about two weeks.