Humpbacks are among the ocean's great travelers, and the ones that gather here have crossed thousands of miles of open sea to reach a bay barely deeper than a swimming pool at its center. That shallowness is the point. Calves are born small and weak, and the bay's protected water shelters them from predators and heavy swell while they grow strong enough for the return journey south. Males fill the season with the long, looping songs for which the species is famous. From a boat - or from the air - you can sometimes see a dozen whales at once, breaching and slapping their fins, the bay alive with the largest animals ever to migrate through it.

In 1774 a Hungarian-born adventurer named Maurice Benyovszky landed on these shores and founded a settlement he called Louisbourg, near present-day Maroantsetra at the head of the bay. Officially he had come to establish a French trading post. Unofficially, he had grander designs. Benyovszky learned the local languages, took sides in local politics, and made himself indispensable - and in 1776 a gathering of Malagasy chiefs formally declared him Ampansacabe, a paramount chief, or king, of the surrounding territory. How much of his claimed kingdom was real and how much was self-invention is still argued. But the title was no idle boast to him.

Benyovszky's ambitions outran his backers. France lost interest, and his independent maneuvering alarmed the colonial government on nearby Mauritius. In May 1786 a French military force landed to shut his operation down. On 23 May, in a brief skirmish, Benyovszky was shot in the chest and killed on the beach he had claimed as the seat of a kingdom. He was thirty-nine years old. The whole episode lasted barely a dozen years - a meteor of a colony that flared and vanished, leaving behind little but a name on old maps and one of the stranger footnotes in the island's tangled history.

Today Antongil Bay is prized for what swims in it rather than who once ruled it. It is the largest and most productive bay in the western Indian Ocean, a breeding ground not only for humpbacks but for sharks and countless other marine species, ringed by the forests of Masoala National Park and the island reserve of Nosy Mangabe near its northern shore. The town of Maroantsetra anchors the head of the bay; the mouth of the Mananara River marks its southern end. It is a place where the wild and the historical sit side by side - a quiet, immense body of water that has cradled both whale calves and the dreams of a self-made king.