Drone-Based Photogrammetry Provides Estimates of the Energetic Cost of Migration for Humpback Whales Between Antarctica and Colombia

Abstract

Monitoring the body condition of animals offers insights into their energetic needs, prey consumption, and vulnerability to environmental pressures. Southern hemisphere humpback whales (Megaptera novaeangliae) depend on Antarctic krill for their annual energy requirements. Drone-based photogrammetry was used to assess the energetic cost of migration and reproduction for breeding stock G humpback whales. Body measurements of 103 adult whales (2017–2019) were used to estimate body condition in Colombia (breeding ground) and the Western Antarctic Peninsula (feeding ground) and seasonal change was predicted. Humpback whales reached their peak body condition between early March and late May, and their lowest between late August and early December. The change in body condition was converted into losses of blubber volume, mass, lipid, energy, and ultimately the biomass of krill required to cover migration. On average, an adult humpback whale lost 36 percentage points of its body condition over the migration, equivalent to 12 m3 or 11,000 kg of blubber tissue, 5000 kg of lipid, 196,000,000 kJ or 57,000 kg of Antarctic krill. By linking migration and reproductive energy costs to krill biomass, our findings provide critical ecological context for understanding how environmental changes such as krill population fluctuations could impact whale populations.