May 30, 2024

The Large-Scale Distribution of Humpback Whales (Megaptera novaeangliae) Wintering in French Polynesia During 1997-2002


Alexandre Gannier


Abstract: The distribution of wintering humpback whales, Megaptera novaeangliae, was investigated during the 1997-2002 period with most data coming from dedicated small boat surveys. In complement, sightings were collected systematically during an opportunistic large vessel survey in 1999, and a sighting program was set up with the French Armed Forces in 2001 and 2002. Every year, dedicated surveys were organized on a 12-m sailboat during the September to November period: a three-observer standard sighting protocol was maintained, with systematic hydrophone sampling to detect singing males. Surveys took place in the Society Islands (the Societies) (1997-2002), Australes Islands (1999 and 2000), Marquesas Islands (2000), and Tuamotu Archipelago (2002). These surveys totaled 12,695 km of effective effort and 2,594 acoustic samples. A total of 129 on-effort sightings were collected, with groups numbering up to six animals, including a calf or juvenile, on 38 occasions. Singers were detected acoustically in three archipelagos, averaging 20.7% of hydrophone stations, with a maximum of 27.0% (Windward group of the Societies) and a minimum of 9.4% in the Tuamotu; no whale was heard in the Marquesas. Although survey effort included offshore waters, whales were mostly (83%) found less than 2 km from the shoreline. All surveyed islands sheltered at least one male humpback, and female/calf pairs were seen in three archipelagos, suggesting that mating occurs over a wide area. The extensive distribution range was confirmed by 29 complementary sightings from the Armed Forces and 17 sightings from the opportunistic survey vessel. The distribution range of whales embodies three archipelagos and a total area of nearly 2,000,000 km2, but humpback whales are marginally present in the Marquesas. The sighting rate for individuals were estimated for inshore waters of different archipelagos from visual data: a maximum of 1.54 whale/100 km was found in the Windward Islands, 1.48 whale/100 km in the Australes, 0.72 in the Tuamotu, and a minimum of 0.35 whale/100 km around the Leeward Islands. These results suggest that humpback whales winter around more than 84 islands in French Polynesia, mostly away from scientific monitoring.

Key Words: boat survey, humpback whale, distribution, acoustics, tropical Pacific, Megaptera

Document Type: Research article

DOI: 10.1578/AM.30.2.2004.227

Page Numbers: 227-236

Info SKU: Vol__30__Iss__2__Gannier Category: