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Searching for humpback whales in a historical whaling hotspot of the Coral Sea, South Pacific

Claire Garrigue*, Solène Derville, Claire Bonneville, C. Scott Baker, Ted Cheeseman, Laurent Millet, Dave Paton, Debbie Steel

*Corresponding author:

ABSTRACT: Humpback whales Megaptera novaeangliaes were severely depleted by commercial whaling. Understanding key factors in their recovery is a crucial step for their conservation worldwide. In Oceania, the Chesterfield-Bellona archipelago was a primary whaling site in the 19th century, yet left almost unaffected by anthropogenic activities since. We present the results of the first multidisciplinary dedicated surveys in the archipelago assessing humpback whale populations 2 centuries post-whaling. We encountered 57 groups during 24 survey days (2016–2017), among which 35 whales were identified with photographs of natural markings (photo-ID), 38 with genotyping and 22 with both. Humpback whales were sparsely distributed (0.041 whales km–1): most sightings concentrated in shallow inner-reef waters and neighbouring off-shore shallow banks. The recently created marine protected area covers most of the areas of high predicted habitat suitability and high residence time from satellite tracked whales. Surprisingly for a breeding area, sex ratios skewed towards females (1:2.4), and 45% of females were with calf. Connectivity was established with the New Caledonia breeding area to the east (mtDNA FST = 0.001, p > 0.05, 12 photo-identification and 10 genotype matches) and with the Australian Great Barrier Reef breeding area to the west (mtDNA FST = 0.006, p > 0.05). Movement of satellite tracked and photo-ID matches also suggest connections with the East Australian migratory corridor. This study confirms that humpback whales still inhabit the Chesterfield-Bellona archipelago 2 centuries post whaling, and that this pristine area potentially plays a role in facilitating migratory interchange among breeding grounds of the western South Pacific.