At the end of June or in early July, humpback whales come up from Antarctica to breed and give birth in the waters surrounding Tahiti, Moorea, Rurutu, and Bora Bora. During late October or November, when the newborn calves are strong enough, humpbacks migrate back to Antarctica.
The peak season to observe whales in French Polynesia is between mid-August and late October. It's the best time to come if you want to see these majestic mammals, their amorous game, and the newborns. Some agencies offer excursions with professionally trained guides who help to ensure the marine mammals are respected and not bothered. If the weather is nice, and the whales are in a resting phase, you can even snorkel with them.
Moorea is perhaps one of the best places for diving or snorkeling with whales. The island usually operates small tours with not more than 20 people per boat. In addition to whales, wildlife encounters in Moorea include dolphins, sharks, and rays. Another great location to swim with humpback whales is the remote Austral Islands. These islands are less touristic and definitely lie off the beaten path.