Humpback whales in super-aggregation in Antarctica

By Louise Murray - 27 Apr 2011 21:10:0 GMT
Humpback whales in super-aggregation in Antarctica

Images Copyright and Credit: Ari Friedlaender.

In a wildlife spectacle, a massive aggregation of over 300 humpback whales followed the biggest swarm of Antarctic krill seen in twenty years into bays in the Western Antarctic peninsula. The humpbacks were gorging on swarms of the tiny shrimp-like crustaceans

'Such incredibly dense numbers of whales and krill have never been seen before anywhere worldwide,' said marine biologist and co lead author of the study, Douglas Nowacek at Duke University, North Carolina. 'Though there were reports of large harvests of animals 100 years ago in the same area, five whales per square kilometre is huge. In the same area later in the year you would expect no more than one animal/km2,' he added.

Such abundance might seem positive, and certainly is for the hungry humpbacks in the short term, but the underlying reasons for the events are climate change driven. The Antarctic ocean remains ice free for longer in the season and that is not good for either species in the long term.

humpback whale in Antarctica

We documented other novel things with the whales, we have started to hear male sexual advertisement calls - adverts of sexual availability normally heard in the calving and breeding grounds far to the north in the tropics,' explained co-author Ari Friedlaender, 'We still do not know where humpbacks actually breed - it may be that they are breeding here when the population is gathered together to feed.' The scientists hope to learn more from the 11 whales that they have tagged. The females need to travel every three years to calve in the warmer waters, but may not need to make that huge migration every year if food remains accessible and available in the south

Previously, during the autumn, the whales had to migrate as the ice formed, protecting the krill that moved into the phytoplankton rich bays to feed in the winter. Almost all life in the Southern Ocean is ultimately dependent on the protein-rich crustaceans, from seabirds, seals and penguins, to the filter feeding whales.

But the krill need the ice to feed on algae that live on its under surface during the winter. No ice, and a year's generation of krill disappear. Krill densities have been falling in tandem with ice cover and while whales can migrate to find food, populations of penguins and seals that cannot forage for great distances will be affected first.

The study was published in the online journal PloS One today (April 27).