Humpback whale migrations to Antarctic summer foraging grounds through the southwest Pacific Ocean (original) (raw)

Humpback whale (Megaptera novaeangliae) populations typically undertake seasonal migrations, spending winters in low latitude breeding grounds and summers foraging in high latitude feeding grounds. Until recently, a broad scale understanding of whale movement has been derived from whaling records, Discovery marks, photo identification and genetic analyses. However, with advances in satellite tagging technology and concurrent development of analytical methodologies we can now detail finer scale humpback whale movement, infer behavioural context and examine how these animals interact with their physical environment. Here we describe the temporal and spatial characteristics of migration along the east Australian seaboard and into the Southern Ocean by 30 humpback whales satellite tagged over three consecutive austral summers. We characterise the putative Antarctic feeding grounds and identify supplemental foraging within temperate, migratory corridors. We demonstrate that Antarctic foraging habitat is associated with the marginal ice zone, with key predictors of inferred foraging behaviour including distance from the ice edge, ice melt rate and variability in ice concentration two months prior to arrival. We discuss the highly variable ice season within the putative foraging habitat and the implications that this and other environmental factors may have on the continued strong recovery of this humpback whale population. Migration is a large-scale class of animal movement driven by resource quality or availability (e.g., breeding habitat, seasonal food resources) 1. Perhaps the most classic concept of migration is the long-distance movements of many birds and mammals characterised by breeding at one end of the migratory pathway and feeding at the other. Most humpback whale (Megaptera novaeangliae) populations undertake seasonal migration, spending the winter in low latitude breeding grounds and the summer foraging in high latitude and productive feeding grounds 2. Historically, our understanding of whale migration has been informed via examination of whaling records and Discovery mark recoveries (a metal tube stamped with a unique serial number, that was fired into the whale, remaining embedded until the whale was captured and flensed 3), which provide a coarse description of the spatial and temporal characteristics of movement. More recently, non-lethal methods such as photo identification (for example 4) and genetic analyses (for example 5) have provided similar point location data. These data, however, provide no detail on the movements in between mark and recapture. Achieving a more detailed understanding of movement has been difficult for marine mammals because they are highly mobile, diving animals that spend relatively little time at the surface 6. Whales are no exception with the majority of movement occurring in remote, often inhospitable, areas with no survey effort 7. The development of satellite tagging technologies has provided an extremely valuable, non-lethal technique to collect high-resolution movement data over biologically relevant time scales 1. For example, satellite tags recently revealed novel migratory pathways of New Caledonia humpback whales that utilise seamount habitats both during the breeding season and while migrating 8. Combining historical whaling and sightings data, Branch et al. 9 hypothesised that pygmy