• Thu
  • Oct 23, 2014
  • Updated: 11:45am

In blue whales' wake

PUBLISHED : Monday, 23 July, 2012, 12:00am
UPDATED : Monday, 23 July, 2012, 12:00am
 

In April, whale watchers off Sri Lanka's southern coast were greeted by an unsettling sight: the lifeless body of an 18-metre-long blue whale. Its nearly severed tail was floating in the water.

From its injuries, it was obvious that Earth's largest animal, which is on the endangered species list, was struck by a ship. It was the sixth death recorded this year in the country. Sri Lanka has both one of the world's busiest shipping lanes and a booming whale-watching industry.

The blue whales may number only in the thousands and researchers want to learn much more about them. That's easier said than done, however: some animals stay in those waters throughout the year when other groups migrate vast distances.

In January, Archer Wong Tik-lung and Matthew Tam Yu-kong, two science students at the University of Hong Kong, spent two weeks in Sri Lanka. They worked with leading marine biologist Asha de Vos and her team. Their mission: to study how ship traffic endangers the graceful marine mammals.

Their field trip was part of Ocean Park Conservation Foundation's University Student Sponsorship Programme, which gives aspiring conservationists a chance to put their newly learned skills to practise.

The duo joined a team of scientists who have been at sea photographing blue whales from December to May for the past three years.

They can recognise individual whales by comparing the unique characteristics on their fins and tail flukes. That way, they keep track of their movements via Google Earth.

The giant animals usually feed by gulping enormous mouthfuls of tiny shrimplike animals called krill near the surface. So they are vulnerable to colliding with both commercial vessels and whale-watching boats loaded with tourists.

'Whales usually surface for air every 10 to 20 minutes, but when the boats get too close, they tend to dive longer and come up less frequently,' Wong explains.

The records will help scientists better understand where and when the whales feed. They hope to persuade the government to shift shipping lanes farther out to sea.

The two students learned to place microphones underwater to record vocal communications between communities of blue whales. The giants rely heavily on their sense of hearing rather than smell and sight. The speed of sound, which travels four times faster in water than in air, makes it the most effective way to communicate, detect prey and navigate.

The whales' calls are of a low frequency and can travel distances as far as 1,500 kilometres. But with increasingly busy ocean traffic, their calls can be drowned out by the noises produced by engines.

One time Wong wanted to listen to the sound of whales nearby; all he could hear was a loud clattering coming from a passing cargo ship.

'I was baffled how one ship at a great distance can mask all other sounds,' Wong says. 'The situation would be even more worrying when the seas are crowded with vessels.'

He says studies have shown that some blue whales communicate through the noisy underwater environment by adopting a lower pitch. But noisy engines can stress the animals out, driving them away to other waters.

Wong wants to enter the conservation or public administrative sector. He hopes he can push for quieter engines with a minimal impact on the environment.

He is particularly intrigued by the whale's tendency to stay in the area even in winter when the waters have less nutrition. That may mean the whales dive down to feed in deeper waters.

'There are whale behaviours that textbooks have yet to explain,' he says. 'There is a world waiting to be discovered. That will be my goal.'

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