Thursday, December 10, 2009

Pitch of Blue Whale Songs is Changing

Photo courtesy: Wikipedia, CC/GFDL

Blue whales are the largest animals ever known to have lived on Planet Earth. They can attain 32.0 m (108’) in length and 172 metric tons (190 short tons) or more in weight. Blue whale calves can weigh 2,700 kg (6,000 lb) at birth – the size of fully-grown hippopotamus – and gain weight at the rate of 90 kg (200 lb) every 24 hours.

Blue whales were abundant in nearly all the oceans until the beginning of the twentieth century. For over 40 years, they were hunted almost to extinction by whalers until protected by the international community in 1966.

There is still such a high demand for whale meat and oil worldwide that hunting whales is an incredibly lucrative business - one carried out illegally by the Japanese. Every year, even with anti-whaling laws in place, there are still intense confrontations between anti-whaling groups and the Japanese whaling fleet. The Japanese hunt whales for consumption under the guise of scientific research.

A 2002 report estimated there were between 5,000 - 12,000 blue whales worldwide. However, more recent research into the Pygmy subspecies of the Blue whale suggests this may be an underestimate. Before whaling, the largest population in the Antarctic numbered approximately 239,000 (range 202,000 to 311,000). The remaining populations are much smaller with about 2,000 individuals in each of the North-East Pacific, Antarctic, and Indian Ocean groups. There are two more groups in the North Atlantic; and, at least two in the Southern Hemisphere.

A high-frequency acoustic recording package, or HARP, used to record marine mammal sounds. Photo courtesy: Scripps Institution of Oceanography.

Using recording equipment such as HARP and other devices, scientists from the Scripps Institution of Oceanography at University of California, San Diego have noticed a change in the pitch in the song of the Blue whale.

Mark McDonald of WhaleAcoustics in Bellvue, CO, John Hildebrand of Scripps Oceanography and Sarah Mesnick of NOAA Fisheries Southwest Fisheries Science Center conducted a study into Blue whale song data from around the globe and discovered a trend. There was a downward curve in the pitch, or frequency, in the Blue whale songs from across the planet. This was not a localized phenomenon; but, was found in all the whale populations off the coast of Southern California, the Indian Ocean and the southern oceans.

To obtain these results, researchers analyzed thousands of songs divided into at least 10 worldwide regions. These include the Northeast, Southwest and Northwest Pacific Ocean; the North Atlantic; the Southern Ocean near Antarctica; and the North and Southeast Indian Ocean.

Researchers had access to a database of Blue whale songs dating back 45 years. These songs have been obtained through scientific and military applications, by seafloor seismometers tracking regional earthquakes and dedicated whale acoustic recording packages.

"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, a professor of oceanography in the Marine Physical Laboratory at Scripps.

There are many potential reasons that could explain the change in pitch; and, for once, the explanation would appear to be positive.

Since the bans on whaling have been in place, the Blue whale seems to have benefitted greatly. The populations have increased in recent years; and, this would seem to be the reason for the pitch change.

Photo courtesy: Flickr, CC

While no one knows conclusively what the function of whale song is, there are some facts they do know. All known singers have been male; and, the high-intensity (or loud) frequency songs and the low-frequency songs travel great distances across the ocean. During mating seasons, Blue whales can be found miles away from each other; so, it may be that the songs identify which species is singing and where they are.

During the height of the whaling years, Blue whale numbers dropped drastically to the point where they have been listed as endangered. With fewer individuals to hear them and greater distance between them, Blue whale males may have found it advantageous to sing higher frequency songs. The researchers believe that this would have maximized their transmission distance to make the location of available females; and, the location of other rival males more effective.

"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.

"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."

Hildebrand says such knowledge about whale songs could be important in monitoring whale populations and recovery efforts.

Hopefully, these changes in whale song mean that we are seeing the resurgence of a healthy, Blue whale population.

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

Via TreeHugger and Scripps Institution of Oceanography

1 comment:

katie said...

i am writing a paper on this at school, i just wanna thank you for posting this, youa re almost the only one that did. this is very informative yet fun and definitely not boring.