Mexico: Cancun: Swimming with the Whale Sharks

One of relatively new attraction in Cancun was swimming with the whale sharks.
Read the article in Lonely Planet, my curiosity urged me to try.
I bought the trip at a ticket booth in downtown for USD 90.
Departed in a port about 20 minutes from the city, I was picked up by a small boat together with other 3 couples.
We departed from the port about 9am.
After about an hour going to the open see, we saw a couple of sea turtles matching.
After about half an hour searching, finally we spotted the whale sharks.
The sea was quite rough for me that I didn't feel well.
I felt afraid to jump into the water, but finally I jump.
But I couldn't get myself breathing well using the snorkel.
I was supposed to swim together with the whale, but instead I just glanced the whale a while, then I decided to get out from the water.
I was not afraid of the whale, but I think I was afraid of the rough sea that I couldn't breathe well using the snorkle.
I remember I went similar trip to watch the dolphin in Zanzibar, Tanzania. The sea was also rough and even I managed to jump into the sea, I couldn't make myself swimming with the snorkle, following the mammals.
I guess this is not my thing... to swim with anything in a rough sea... I expected I swam in a quite tranquile sea over the whales... but I should understand now that open sea couldn't be quite and tranquile...
On the way back, we stopped in a tranquile area in the sea to do snorkling and have beers and ceviche.