WATCH: 30-foot whale shark surprises fisherman: 'Biggest I've ever seen in the Gulf'

BRADENTON, Fla. (WFLA) – Jon Royster was on a fishing trip near Anna Maria Island, on Florida's Gulf Coast, when he and his fellow fisherman encountered a large whale shark last weekend.

Royster, of West Bradenton, who was aboard the vessel with Captain Lance of Florida Fishing Fleet charters, was on the water when three large whale sharks came up to the boat — something they never expected,

"Biggest I've ever seen in the Gulf in 15 years," Lance said.

"I have seen so many cool things since I've been down here, from the whale shark to a giant manta ray to even a giant leatherback turtle. Just some incredible things," Royster said.

The whale shark, the largest fish in the sea, weighs 20.6 tons on average and can reach lengths of 40 feet or more.

Like many whales, the shark filter-feeds and typically eats plankton with its lengthy, gaping mouth while swimming close to the surface of the ocean, according to National Geographic.