Drones tracking whales reveal they lose tons during annual migration

By Stephen Beech

Humpback whales lose more than the weight of two adult elephants during their annual migration, reveals new research.

They shed an average of 11,000 kilos (24,250 lbs) of blubber - more than a third of their body fat and equivalent to the energy obtained after feeding on 57,000 kilos (125,664 lbs) of krill - during their epic ocean-spanning journey, say scientists.

Researchers used drones to monitor the body condition of 103 adult humpback whales in the southern hemisphere during their "feast and fast" migration.

The team used data from the drone monitoring to determine the whales’ body conditions on their breeding ground in Colombia and on their feeding ground on the Western Antarctic Peninsula, a highly productive krill region of Antarctica.

Each adult whale lost around 36% of its body condition during migration, according to the findings published in the journal Marine Mammal Science, or 196 million kilojoules of energy, equivalent to the energy consumed by an average adult human over 62 years.

Study leader Alexandre Bernier-Graveline says the findings highlight the importance of managing their krill-rich feeding grounds.

Bernier-Graveline, a doctoral candidate at Griffith University in Australia, said: “Southern hemisphere humpback whales depend on Antarctic krill for their annual energy requirements, fuelling their long migrations between feeding and breeding grounds.

“We found the whales were at their fattest in early autumn – March to May – and slimmest by late spring – August to December – showing a dramatic seasonal change in body condition.

“Our study quantifies the whales’ extreme ‘feast and fast’ lifestyle, and the critical role of Antarctic krill in their survival and migratory life-history strategy.”

With the Antarctic sea-ice ecosystem rapidly changing, he says understanding migrating whales' energy demands helped scientists assess how environmental changes - such as krill availability or climate shifts – could impact whale populations.

Bernier-Graveline added: "By linking migration and reproductive energy cost to krill biomass, the findings provided key ecological contexts for understanding how environmental changes such as krill population fluctuations could impact whale populations in the future."