Dear Sarah;-
   Live Eps will probably not be far from the dead ones that one
finds on the beach. But off-shore snorkeling around Sanibel appears
not to have clearness at more than a few feet. My advice is: if
snorkeling, don't look for the eps, but rather look for sea anemones.
That's what they feed on and are rather larger than the Eps. If you
find some, scrabble about the base.
  The other bit of advice I would give is to go visit the Bailey-
Mathews shell Museum and talk to Jose Leal about your problem. He
knows most of what there is to know about Sanibel.
     Art