Sophie swims up, taps me on the arm, and points to a trio of bright-yellow butterfly fih nibbling on a stand of cauliflower coral. A gang of convict surgeon fih hurry by as if they were late for an appointment, followed by the comical unicorn fih. The sound of our laughter travels up our snorkel pipes. Apparently we've hit upon a secret call because more turtles appear and rise to the surface. If we hadn't been told not to, we could reach out and touch them.

We see those venerable green turtles the next day, too, a few miles past Turtle Town, just below the state park and the bay that is named for Jean-François de Galaup, Comte de La Pérouse, the first European to come to Maui. Unlike La Pérouse, who sailed in a five-hundred-ton ship with a crew of 114, we are day-trippers on a single-masted catamaran called the Kai Kanani, which has up to forty-one passengers and five personable young crewmen under the direction of Captain Roger Gildersleeve, who has plied these waters for more than two decades. Over breakfast of fresh pineapple, watermelon, and sweet breads, as the boat heads south, Captain Roger fils us in on La Pérouse, who briefly explored along Maui's southwest coast in 1786. Halfway into his disquisition, though, minutes after we've passed the island's last lava flow, he suddenly stops and points, and sure enough, right in front of us two humpback whales, a calf and its mother, rise up, stretch, and splash back into the water. Everyone watches, transfied, and waits for the whales to breach again.

While we scan the water, Captain Roger explains how the humpbacks come here from Alaska every winter to breed; that a calf gains, on average, a hundred pounds a day from its mother's milk; and that full-grown it will weigh about eighty thousand pounds.

"One o'clock, one o'clock," someone calls out, and we shift our attention starboard, watching as two pairs of flukes, each the size of a living room sectional, waggle and disappear. They look like submarines. In between our gasps and exclamations, Captain Roger continues his whale talk, mentioning that humpbacks are the fifth-largest whale species; that they feel protected in the ocean between Maui, Lanai, and Molokai; and that individual humpbacks are distinguishable by the unique pattern on their tail flukes. For Sophie and me, this is all review since we're fresh from the smart, modern aquarium, the Maui Ocean Center, which has a dedicated whale room.

Sails still furled since there is no wind, the Kai Kanani chugs ahead. Off to the left, mountains the color of billiard-table felt rise gradually; somewhere behind them, at 10,023 feet, is Haleakala's summit. Off to the right is another pod of humpbacks, topographical in their own fleeting way. We pass one of the ancient Hawaiian villages where La Pérouse found a thriving culture, and an unlikely series of freshwater wells, and then we turn, as the land angles right, and set anchor.

"Pool's open!" Captain Roger shouts as the crew hand out masks and flippers.