TO CLOSE

A study done by researchers on marine mammals reveals that dolphins can cooperate and perform tasks together. (November 23)
AP

Highlights of history

  • A heat wave reduced the survival rate of dolphins by 12%.
  • The results of the study are a stark reminder of the negative effects of climate change
  • Climate change can have a significant impact on the survival of many other marine mammals.

The favorite marine mammals of all like to stay cool, but the burning seawater seems to be wreaking havoc on dolphins in some parts of the world, new study suggests.

Scientists first noticed the problem after the 2011 heat wave in Australia: unusually warm seawater off the west coast of Australia was followed by a significant decrease in the number of dolphins next six years. By following hundreds of dolphins during this period, scientists also discovered that the heat had reduced the mammalian survival rate by 12%.

"The extent of the negative influence of the heat wave surprised us," said the main author of the study Sonja Wild in a report. "It is particularly unusual that the breeding success of females does not seem to have returned to normal even after six years," said Wild, Ph.D. student at the University of Leeds in the UK

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A dolphin jumps from Shark Bay, in the west of Australia. A new study suggests that seawater heated by climate change threatens dolphins and other marine mammals. (Photo: Simon Allen)

The dolphins studied live in Shark Bay, a UNESCO World Heritage Site in Western Australia. During this hot period of 2011, temperatures in the bay were up to 7 degrees Fahrenheit above average, scientists said. The extreme heat has damaged seagrass beds, a vital part of the bay's ecosystem, which provides food and shelter for its inhabitants.

"Our results suggest that extreme weather events may be too sudden or disruptive for even highly adaptable animals to react," co-wrote a study. Simon Allen of the University of Bristol in the UK said.

Ocean fish species are also threatened by climate change: a study in February found that global warming has reduced populations of many fish species around the world.

Farewell fish and chips ?: Atlantic cod, many other fish diminish as the globe warms

Some good news from Monday's study: the heat wave did not have the same effect on all dolphins. Dolphins that use sponges as tools – a technique that helps dolphins locate deep-sea foods – have not been as affected as those who do not use this technique.

Still according to Wild, the decline in dolphin populations "is a stark reminder of the negative effects of climate change".

In fact, even beyond dolphins, climate change may have more profound consequences on the survival of many other marine mammal species than previously thought. "Marine heat waves are likely to occur more frequently in the future because of climate change," said the study's co-author. Michael Krützen, anthropologist at the University of Zurich in Switzerland.

A dolphin jumps out of water in Shark Bay, Australia. (Photo: Simpn Allen)

"This is worrying not only for the long-term prospects of marine mammal populations, but also for the entire ocean ecosystem," he said.

The study was published Monday in the peer-reviewed scientific journal Current biology.

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