Humpback whale population connectivity, movement, and biology

Overview

Understanding how humpback whale populations connect across ocean basins — and how they change over time — is fundamental to assessing population structure, gene flow, and the resilience of recovering populations. My research spans both the connectivity between distant breeding populations and the long-term monitoring of the eastern Australian (E1) population, drawing on photo-identification and decades of accumulated survey data.

Population connectivity and movement

Australia–Brazil connectivity (2026): Using photo-identification and genetic analysis, I co-led the documentation of a humpback whale that moved between the eastern Australian (E1) and Brazilian (B) breeding populations — the longest recorded inter-oceanic movement of any individual whale. This finding reveals unprecedented connectivity between what were previously considered separate breeding populations and has significant implications for international conservation management.

Southern right whale range extension (2024): Co-authored the first confirmed sighting of a southern right whale north of the equator, a remarkable range extension for the species.

Long-term population biology

I study the behavioural ecology of the eastern Australian and Hawaii humpback whale populations. This includes a historical analysis of decades of distribution data in Hervey Bay, Queensland — a critical migratory stopover — the characterisation of social groups, including groups containing multiple mother–calf pairs, and the first documented observation of sexual behaviour between two male humpback whales. Together these studies track how humpback whales use key habitats at different life history stages.

Implications for management

These findings demonstrate that international coordination is essential to the conservation of humpback whale populations, and that sustained long-term monitoring of key habitats is needed to detect change in distribution, abundance, and demography.

Selected publications

• Castro*, Stack* et al. (2026) — First evidence of bidirectional exchange between distant humpback whale breeding populations in eastern Australia and Brazil. Royal Society Open Science. DOI: 10.1098/rsos.260251 (*joint first authors)
• Stack et al. (2019) — Distribution patterns of east Australian humpback whales (Megaptera novaeangliae) in Hervey Bay, Queensland: a historical perspective. Australian Mammalogy. DOI: 10.1071/AM18029
• McGovern et al. (including Stack) (2025) — Prevalence, composition, and behaviour of humpback whale groups containing multiple mother-calf pairs in East Australia. Aquatic Mammals. DOI: 10.1578/AM.51.2.2025.163
• Stack et al. (2024) — An observation of sexual behavior between two male humpback whales. Marine Mammal Science. DOI: 10.1111/MMS.13119
• Castro Ayala et al. & Stack (2024) — New northernmost distribution records of the Eastern South Pacific southern right whale. PLOS ONE. DOI: 10.1371/journal.pone.0312528