Ok, I just have to toss my 2 cents into this lively debate.
I have collected animals from the coast of NC for many, many years. Not comercial, but a few here and a few there for my own tanks.
Most notable things I have collected from the south coast of North Carolina.
Blue striped hermit crabs from the mudflats at low tide. Great for a FOLR setup, as these guys are the meanest, nastiest hermits you can find. They get quite large too. Not for a reef tank, and will eat any fish they can catch. I say they are good because they will eat any scraps of food in the tank.
Purple urchins - got one of these, and sold it after about a year. It systematicaly ate every scrap of corline algae off of my live rock in my tank. Very pretty, but very destructive. Very hard to pick up too, those spines hurt.
Conch looking snails. I can't remember their real name, but they look like little 2 inch conch snails. They are reef safe and behave just like a queen conch. Good find, look in the tide area at night for them in the sand. They leave little tracks in the sand and usually about 2 inches down in it.
Now, for the part that will probably piss everyone off. Many years ago, I had a rather large white spot green moray eel. I could not keep anything else in the tank with him, it was his tank. He even attacked and killed a large lion fish. One year while at the beach, I was fishing and kept catching all these real tiny spot and croakers. Too small to eat, anyway. So, I kept 10 of them the last day I was there and drove them home to see if they could live in my tank with Homer, that big eel.
Well, 2 died during the 4 hour trip home. I put the rest into the 55 gallon tank and 2 more didn't make it during the first night.
So, out of 10, 6 survived one week. Not good odds, if you ask me. Anyway, then I noticed one was missing. Then I noticed Homer was really fat. So, I fed the little shrinking school of fish regular fish food and Homer would grab one a month. The next year, I did the same thing with about the same results. Homer was happy with the arrangement anyway. The spot and croakers schooled too, it was pretty to watch the tank and know that I didn't pay any money for what was going to end up as eel food.
I would be a whole lot more careful if I had a reef tank, and quarantine is a must if you do this.
As for collecting on dive trips - if the trip is to a site more than 6 miles out, you can do pretty much whatever you want to do. I have personally spearfished for spadefish in the Chesapeke bay on a dive trip, and no one said a word to me.
As far as I know, there is no 'limit' on what you can collect in international waters. Collecting inside state parks, like John Pennycamp in FL where I dive a lot, is prohibited, but if you do a dive in *non-state park* water, I believe you can collect whatever you want to.
David