June 22, 2024

Observations of Longman’s Beaked Whale (Indopacetus pacificus) in the Western Indian Ocean


R. Charles Anderson, Rebecca Clark, Peter T. Madsen, Chris Johnson, Jeremy Kiszka, and Olivier Breysse


Abstract: Seventeen new sightings, and a total of 32 records, of the little-known Longman’s beaked whale, (Indopacetus pacificus) (also called tropical bottlenose whale or Indo-pacific beaked whale) are reported from the western Indian Ocean. Field identification features are reviewed, and the possibilities of confusion with other beaked whales are noted. Mean group size for the western Indian Ocean sightings was 7.2 individuals (n = 22, SD = 10.9, range = 1 to 40). This is smaller than previously published estimates from the Pacific, reflecting a relatively large number of new sightings of individuals and small groups, which, in turn, reflect the recent description of the external appearance of this species. Recorded dive times were either short (mean = 14 min, range = 11 to 18 min, n = 5) or long (mean = 26 min, range = 20 to 33 min, n = 19). Longman’s beaked whales appear to be widely distributed in the warmer (> 27º C) waters of the western Indian Ocean, but most sightings were over or adjacent to deep slopes (depths 250 to 2,000+ m). Mean sighting rates were much higher in the western Indian Ocean (1 sighting per 31 sea days for visual surveys) and particularly around the Maldives (1 sighting per 21 sea days) than have been reported from the Pacific (1 sighting per 200 sea days). Longman’s beaked whales may therefore be more common in the western Indian Ocean than in the Pacific, although survey methodologies used in the two oceans were not identical. Widespread gillnet fisheries may pose a potential threat to this species in the Indian Ocean.

Key Words: Longman’s beaked whale, tropical bottlenose whale, Indopacetus pacificus, Maldives, western Indian Ocean

Document Type: Research article

DOI: 10.1578/AM.32.2.2006.223

Page Numbers: 223-231

Info SKU: Vol__32__Iss__2__Anderson Category: