Is the population of the blue crab increasing or decreasing over time?

It would probably depend on whom you ask. But back in the late 90's there were some conditions put on crabbing.

I don't know if this happens every where, but in Houston Texas, if you are crabbing, you are not allowed to take the females. If you catch any, you must throw them back in. And yes, it is real easy to tell the females from the males.

Turn the crab over and on there belly there is a "V" shaped flap, the female's is wider than the males.