9 April 2013

They swam north to survive


Many of the large land mammals, such as mammoths and woolly rhinos, didn’t survive the last ice-age. In contrast ocean mammals such as the bowhead whale, which with a lifespan of 200 years is the world’s longest living mammal, did. According to the first study on what happened to large marine mammals in this period, they did this by tracking the changing sea ice distributions, and moving their range north as the ice coverage of the northern oceans shrank. These results from University of Copenhagen and Albert-Ludwigs University in Germany are about to be published in the journal Nature Communications.

- The survived the last glaciation in contrast to many of the large land mammals. Today they are in general protected and recovering from past hunting. But ongoing climate change may hamper this recovery for the bowhead whale. Predictions show that 50% of their habitat will be gone by the end of the 21st Century.
Andy Foote, Geneticist, Basic Research Centre for GeoGenetics at the Natural History Museum of Denmark, University of Copenhagen.

The warm sets in

Over the last 3 years, Dr Andy Foote and Professor Tom Gilbert from the University of Copenhagen, and Kristin Kaschner from Albert-Ludwigs University in Germany and a team of other collaborators studied what happened to these 18m long, 100 ton whales and their relatives, as the ice sheets that once covered northern Europe retreated.

Andy Foote says on the results:

- We have analysed 44 subfossil bone samples collected over a geographic range from the Dutch coast and 1000 km north of this, and spanning the period of 50,000 to 11,000 years ago, when the post ice age climate change led to a global increase in temperature. We found that unlike most land mammals, the bowhead whale actually increased in genetic diversity at the end of the ice age. This could be due to the number of whales increasing - and we did also estimate a three-fold increase in their ideal habitat at this time that would support this - however, it could also be due to a sudden increase in connectivity between ocean basins as the ice barriers melted, with bowhead whales swimming from the Pacific into the Atlantic.

Saving energy

11.000 years ago, the environment off Northern Europe was similar to Greenland is today. And while many of the land mammals were not able to cope as this environment changed and the warm set in, the whales managed to survive.

Whale skeleton - Photo: Birgitte Rubæk

Professor Tom Gilbert, University of Copenhagen, explains:

- In contrast to larger land mammals, there is a relatively simple explanation as to why the whales survived the changes, while the mammoths, woolly rhinos and so on went extinct. The aquatic environment that they live in makes long range movement energetically inexpensive, and thus enabling them to track their shifting habitat with relative ease. In contrast, movement was much harder for the land mammals – and in addition to that they may have faced pressures such as human hunting.

No bright future

Unfortunately however, long-term recovery for the bowheads seems uncertain. As with polar bears, their habitat is shrinking with continued global warming. Thus although commercial whaling ceased in the 1930s, with only a very limited catch permissible off Greenland today, it may be that future climate change now poses a new and imminent threat. The researchers’ analyses show, that the size of their natural environment will halve over the next 100 years alone. Therefore measures to reduce the progress of global warming are needed to ensure the long term survival of this Arctic giant.

The research was done as a collaboration lead by the University of Copenhagen in Denmark, and Albert-Ludwigs University in Germany.

Read more: http://www.nature.com/ncomms/journal/v4/n4/full/ncomms2714.html


Dr. Andy Foote
Phone: +4552323841

Professor Tom Gilbert
Phone: +4523712519