Abstract
Humpback whale populations migrate extensively between winter breeding grounds and summer feeding grounds, however known links to remote Antarctic feeding grounds remain limited in many cases. New satellite tracks detail humpback whale migration pathways from Western Australia into the Southern Ocean. These highlight a focal feeding area during austral spring and early summer at the southern Kerguelen plateau, in a western boundary current where a sharp northward turn and retroflection of ocean fronts occurs along the eastern plateau edge. The topographic steering of oceanographic features here likely supports a predictable, productive and persistent forage ground. The spatial distribution of whaling catches and Discovery era mark-recaptures confirms the importance of this region to Western Australian humpback whales since at least historical times. Movement modelling discriminates sex-related behaviours, with females moving faster during both transit and resident periods, which may be a consequence of size or indicate differential energetic requirements. Relatively short and directed migratory pathways overall, together with high-quality, reliable forage resources may provide a partial explanation for the ongoing strong recovery demonstrated by this population. The combination of new oceanographic information and movement data provides enhanced understanding of important biological processes, which are relevant within the context of the current spatial management and conservation efforts in the Southern Ocean.
Highlights
Recovery patterns following intensive industrial whaling vary across populations, with differing levels of uncertainty, but the recent comprehensive assessment by the IWC Scientific Committee projected the Western Australian (WA) population to have the highest abundance, in the range of 18,415–24,91814
The migration pathways of the WA humpback whales tracked into the Southern Ocean (n = 12, Fig. 1) show whales left Australian coastal waters during the austral spring, generally between mid-September and early October
One female headed to the northern Kerguelen plateau (ID131140); one continued in a more southward route towards the ice edge, staying east of 95°E (ID154859); only intermittent records appeared from ID154876 near 102°E, 52°S; and one tag failed during early transit (ID112744; at 96°E, 42°S)
Summary
Recovery patterns following intensive industrial whaling vary across populations, with differing levels of uncertainty, but the recent comprehensive assessment by the IWC Scientific Committee projected the Western Australian (WA) population to have the highest abundance, in the range of 18,415–24,91814. We show directed movements towards the southern Kerguelen plateau, a known area of high biological productivity[34,35,36], including a focal usage of the western boundary current[37,38,39] by both male and female HBWs. Using hidden Markov models, we discriminate sex-related movement behaviours, and examine residency behaviour in relation to current Southern Ocean management areas and a proposed Marine Protected Area. Using hidden Markov models, we discriminate sex-related movement behaviours, and examine residency behaviour in relation to current Southern Ocean management areas and a proposed Marine Protected Area We consider this new information within the historical context of the spatial distribution of whaling catches, and what is known of other HBW movements in the region. We conclude that the southern Kerguelen plateau region is likely to provide a predictable, persistent and high-quality forage resource[36,37,40], and usage of this area by WA HBWs may provide a partial explanation for the ongoing strong recovery of this population
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