Searching for humpback whales two centuries post-whaling: what is left in the Chesterfield-Bellona archipelago?
Claire Garrigue, Solene Derville, Claire Bonneville
International Whaling Commission
Humpback whales were severely depleted by commercial whaling, and understanding key factors of their recovery is a crucial step for their conservation worldwide. In Oceania, the Chesterfield-Bellona archipelago was identified as one of the primary humpback whale whaling sites of the 19th century. However, given its remoteness, it has remained almost unaffected by anthropogenic activities since then. In this study, we report on the first large-scale multidisciplinary dedicated surveys conducted in the Chesterfield-Bellona breeding area to assess the current status of its humpback whale population, two centuries post-whaling. In 2016 and 2017, two surveys were conducted, totalizing 24 days of effort and 57 groups encountered, among which 13 whales were identified though photo-id, 16 through genotyping and 22 with both methods. A total of 6 whales were equipped with satellite tracking devices. Though humpback whales still appear to visit the area during austral winter, especially the inner shallow waters of the reef complex and the neighbouring off-shore shallow banks, their density was relatively low (0.041 whales/km surveyed on average). Surprisingly for a breeding area, the sex ratio was very skewed towards females (1:2.8). A large proportion of the groups encountered included a mother and calf (45%), especially in the most sheltered waters south of the Chesterfield plateau. Photo-IDs and genetic comparisons suggest a strong connectivity with the New Caledonian South Lagoon breeding area. Although no match was detected to-date with the Australian Great Barrier Reef, a connectivity with the South East Australian migratory corridor is suggested by the tracking of three females (including one with calf).