Snorkelling for a regular sim doesn’t collect anything as far as I can see, they just swim about with the snorkel equipment on which I can’t remember the name of.
If regular sims want to collect shells they have to go scuba diving. (Which itself makes no sense)
I really don’t like that the diving activities are separate. I.e treasure hunting, spear fishing, shell collecting and taking photos underwater. It feels like just a cheap way to pad it out because we can’t see anything other than a buoy and a few bubbles in the surface.