I don't know any dive site names there in Plymouth, but I can tell you that the bay (cove??) area adjacent (1/4 - 1/2 miles offshore?) to the Plymouth nuclear power plant proved fruitful and interesting on my first ever post-c-card dive a few years ago. To my shock, glee, and adrenaline-overload, my cousin bagged a 6 lb. monster bug, which must've tasted damned good, and looked 20% larger than it was. Alas, I commuted in, had to rush out so couldn't share in the feast.
The size and number of the bugs there are rumored to be attributable to the warm water pumped from the nuclear plant itself. Gene mutation, anyone?? I'd like to log the name if one exists, or at least have a proper BS story to pass along to the grandkids. Curious also if there's any truth to the correlation of warm-water discharge/temperature variation to bug size/reproductiion rates?
Would love to go back to Plymouth or anywhere down by pre-bridge Cape Cod, anytime soon, anytime later, job permitting I'm there with fins on.
Eggman