The largest shark's eye in the photo is 2" long and was found on Cayo Costa last year. Cayo Costa is an island accessed by boat only and is north of Captiva and Sanibel Islands. This shell is also known as tiger's eye. You may not want to bleach them to preserve the exterior. But if they're already sunbleached, then it won't matter. You can always shine them up a bit by putting a coat of artist quality varnish on them.
I've been in love with having sand between my toes since I was a teenager taking the ferry across the bay to arrive at Presque Isle State Park (aka The Peninsula) in Erie, PA.