Alan,
In the days of the old Fish Market we had crabs & shrimps of a weekend when I was a kid. We couldn't afford lobster and the price is through the roof now, wherever you go and especially on this Mediterranean island. Both large crabs and lobsters were available and affordable into the early 1960s, but not since. As for the rest - oysters, cockles, whelks, mussels - you're welcome to them. For many years now it has been difficult to find large crabs - they just don't seem to reach maturity any longer, probably due to over-fishing.
Later on this afternnon we have heavy rain forecast for a couple of days. That will bring out the snails, to which you are very welcome, but not me thanks. Then for the next couple of days I will be busy knocking them off the walls of the house with a broom!
Maurice