Spatial Ecology of Humpback Whales in the South Pacific

Abstract

The humpback whale (Megaptera novaeangliae) is a cosmopolitan and migratory species that inhabits high-latitude regions for summer feeding, and low-latitude regions for winter breeding. The spatial ecology, which involves investigation of the relationships between spatial entities and ecological phenomena, has been described for humpback whales in a wide range of habitats. However, until now, habitat-use of the endangered humpbacks in their South Pacific breeding grounds has not been investigated. This region spans from New Caledonia to French Polynesia, and contains many differing geographic features that vary continuously across the region; but natal fidelity is restricted to only a few areas. Non-systematic boat-based surveys conducted in the South Pacific breeding grounds of Tutuila, American Samoa (2003 – 2010) and Vava’u, Tonga (1991 – 2009) revealed the presence of all breeding ground group-types during the winter, confirming that these regions are important for hosting the reproductive activities of calving, courtship, and singing. The collection of individual identification photographs (n = 788) and biopsy samples (n = 334) during annual seasons in Vava’u revealed betweenseason resights of 101 individuals, implying site fidelity to this breeding ground is prevalent. I used ArcGIS to examine the relationship between the location of humpback whale group sightings in Tutuila (n = 334, 2003 – 2010) and Vava’u (n = 564, 1996 – 2007), and the environmental variables that constitute both breeding grounds, to predict areas of favourable habitat. Kernel density analyses and Maximum Entropy modelling were used to assess whether: 1) differences in distributional patterns between breeding ground group-types were evident; 2) differences between areas of habitat suitable for mother-calf pairs, adults, and singers were evident; 3) environmental variables varied in their importance for discerning habitat suitable for mother-calf pairs, adults, and singers. Depth of water was important for predicting suitable mother-calf habitat in both sites, which was restricted to shallow, near-shore waters. Conversely, access to deep water was important for adult groups. Additionally, slope and rugosity of the sea floor were informative for the prediction of suitable singing habitat. My research identifies areas of important fine-scale habitat for humpback whale breeding activities within the South Pacific for the first time. This will be a useful contribution to the large-scale whale sanctuaries throughout the South Pacific, to ensure adequate protection of Oceania’s humpback whales.