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Ditto and Roatan.....If it doesn't have to be Club Med, your timeframe puts you in the prime Whale Shark Diving season near Gladden Spit in Belize. It's only when the Cubera Snapper spawn near the full moon(s) - the Whale Sharks go there to feed then.
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Several of the nearby atoll resorts and several of the resorts farther north also go there. But if they do, it's probably going to be $150 or more in additional cost per single dive trip since they're farther away. And there's no guarantee so you can pay a lot for a long boat ride on an average reef.
There's also a slight chance of snorkeling with Whale Sharks off Utila in May but they're more reliably seen there in March/April. That can be a very reasonable trip since it's also a dive training/backpacking location so accommodations in town are cheaper. A little harder to get to either from mainland Honduras or thru Roatan.
I'm pretty sure the Humpbacks are only around the Dominican Republic in winter. The liveaboards from Turks/Caicos move over there during Jan-March to snorkel with them there at the Silver Banks off Puerto Plata. They also go by Grand Turk on the way there but that would be a short plane ride over from Club Med Turkoise. Obviously earlier than you can go since it's likely happening now.
We saw a lot of sharks off Turks/Caicos - especially out at West Caicos or French Cay. But nothing larger. I believe Club Med does most(all?) of their diving off Provo's NW Point - good diving but less likely for sharks. If JoJo is still around you might see a dolphin.
I've heard they get lots and lots of boats out there.Greenliger, are you saying you were there in off season and it was a slow week but the island was still overcrowded or did you mean the whale shark snorkel trip was crowded? What month/week were you there please?
Unless things have changed, you're permitted to dive with whale sharks in the Galapagos and for at least a few months out of the year, they're virtually guaranteed at Darwin. Saw them on just about all our dives there in June '04 and August '07.Most of the world's whalesharks or whale "hostspots" have regulations in place that prohibit scuba diving with these larger animals. Snorkeling is really the only way to go when you are going to places with more or less guaranteed encounters with the animals.