Abstract
Humpback whales (Megaptera novaeangliae) are known for their nearshore distribution during the breeding season, but their pelagic habitat use patterns remain mostly unexplored. From 2016 to 2018, 18 humpback whales were equipped with depth-recording satellite tags (SPLASH10) to shed light on environmental and social drivers of seamount association around New Caledonia in the western South Pacific. Movement paths were spatially structured around shallow seamounts (<200 m). Indeed, two males stopped over the Lord Howe seamount chain during the first-ever recorded longitudinal transit between New Caledonia and the east coast of Australia. Residence time significantly increased with proximity to shallow seamounts, while dive depth increased in the vicinity of seafloor ridges. Most of the 7,986 recorded dives occurred above 80 m (88.5%), but deep dives (>80 m, max 616 m) were also recorded (11.5%), including by maternal females. Deep dives often occurred in series and were characterized by U-shapes suggesting high energy expenditure. This study provides new insights into the formerly overlooked use of pelagic habitats by humpback whales during the breeding season. Given increasing anthropogenic threats on deep sea habitats worldwide, this work has implications for the conservation of vulnerable marine ecosystems.
Highlights
Seamounts are recognized as important pelagic ecosystems and a major biome in the open ocean[1]
Humpback whales of New Caledonia and Australia are separated by the Coral Sea, a vast pelagic space stretching over more than 1,500 km covered with seamount chains and ridges, where marine megafauna distribution is poorly understood
Understanding the role played by seamounts in the distribution and movements of humpback whales in the open ocean is a prerequisite to effective management at the scale of giant marine protected areas (MPA) such as the recently created “Natural Park of the Coral Sea”
Summary
Seamounts are recognized as important pelagic ecosystems and a major biome in the open ocean[1]. Humpback whales seasonally migrate from the polar feeding grounds where they spend the summer, to the tropical breeding grounds where they mate and give birth during the winter While they must spend extended periods of time in the open ocean, their habitat use patterns have primarily been studied nearshore[14,15,16,17,18,19,20,21]. In the western South Pacific, humpback whales were found to visit shallow seamounts in the late breeding season[11]. The endangered Oceania population of humpback whales[23] includes the sub-population wintering off New Caledonia (and labelled by the International Whaling Commission as sub-stock E228), which occupies the most western region of the South Pacific[29] This region is neighboured by the East Australian coast where sub-stock E129,30 migrates. Humpback whale movements and diving are analysed in relation to seamounts to understand their unique association with these ecologically important pelagic features
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