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Whales no longer singing the blues?

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December 15, 2009

Fred Benko - National Oceanic and Atmospheric Administration (NOAA) Central Library

Fred Benko - National Oceanic and Atmospheric Administration (NOAA) Central Library

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Endangered blue whales appear to be singing a happier song according to researchers studying the haunting sounds these huge mammals broadcast beneath the waves. Specifically, a drop in frequency has been noticed and a list of possible causes have been examined - from climate change to a rise in human-produced ocean noise - but it seems the explanation could actually be a positive one. It's believed the drop may be caused by the increase of blue whale numbers following bans on commercial whaling activities … in other words, the males don’t need their voices to travel as far to attract a mate.

According to the research, the sound level of songs blue whales sing across the vast expanses of the ocean to attract potential mates has been steadily creeping downward for the past few decades. Scientist and professor of oceanography John Hildebrand at Scripps Institution of Oceanography at UC San Diego and his colleagues believe the trend may be good news for the population of the endangered marine mammal.

Hildebrand, along with Mark McDonald of WhaleAcoustics in Bellvue, Colorado, and Sarah Mesnick of NOAA Fisheries Southwest Fisheries Science Center studied blue whale song data from around the world. They discovered a downward curve in the pitch, or frequency, in the songs of blue whales around the globe, from off the Southern California coast to the Indian and Southern Oceans.

“The basic style of singing is the same, the tones are there, but the animal is shifting the frequency down over time. The more recent it is, the lower the frequency the animal is singing in, and we have found that in every song we have data for,” said Hildebrand.

Reasons unknown

Blue whale songs have been recorded for the past 45 years through scientific and military applications by seafloor seismometers tracking regional earthquakes and dedicated whale acoustic recording packages but we still don’t know the function of blue whale songs. Scientists do know that all singers have been males and that the high-intensity, or loud, and low-frequency songs can travel long distances across the ocean. Blue whales are widely dispersed during the breeding season and it is likely that songs are used to advertise which species is singing and the location of the singing whale.

Before blue whales were protected from commercial whaling, their numbers shrank alarmingly and it is thought that the males of the species sang higher frequency songs in order to maximize their transmission distance and their ability to locate potential mates (females) or competitors (other males), say the researchers.

“It may be that when (blue whale) densities go up, it’s not so far to get to the closest female, whereas back when they were depleted it may have been that the closest female was a long way away,” said Hildebrand.

He believes that in the 1960s, when blue whale numbers were at their lowest and first recordings of the animals were made, the males chose to sing higher frequencies that were louder and heard over greater distances.

“When they make these songs they need to use most of the air in their lungs,” said Hildebrand. “It’s like an opera singer that sees how long he can hold a note. The (male) songs are made to impress the females and/or other males, so I think that’s how the boy blue whales are impressing the girls, or are showing off to other boys: by making a loud and long song.”

The scientists say the same downward pitch phenomenon may be true in other whales such as fin and humpbacks. Hildebrand says such knowledge about whale songs could be important in monitoring whale populations and recovery efforts.

During the study the researchers analyzed thousands of blue whale songs divided into the Northeast, Southwest and Northwest Pacific Ocean; the North Atlantic; the Southern Ocean near Antarctica; and the North and Southeast Indian Ocean.

The study’s results are published in the most recent issue of the journal Endangered Species Research.

This research was funded by the U.S. Navy, NOAA and the National Science Foundation.

Want to hear what a blue whale song sounds like - Wikipedia has some fascinating recordings.

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