Nuclear bomb detectors reveal hidden population of blue whales

A rare spot of a blue whale tail fluke. Credit: Mike Baird. Accessible via Wikimedia Commons. CC BY 2.0.

Blue whales may be the largest animals on the planet, but they’re hard to spot. The 20 commercial whaling industrye century brought them to the brink of extinction, and today they are listed as endangered under the Endangered Species Act. A blue whale can weigh up to 33 elephants, but many go unnoticed because their numbers are small and they live mostly solitary in all oceans except the Arctic. Yet earlier this year, a team of scientists reported finding a new population of pygmy blue whales in the middle of the equatorial Indian Ocean, using nuclear test detection equipment.

“The discovery would not have been possible otherwise,” said Emmanuelle Leroy, referring to the underwater microphone array that “listens” to sound waves indicative of underwater explosions. Leroy is a bioacoustician – a scientist who studies how animals create and perceive sound – and lead author of the study on the discovery of the pygmy blue whale. (Pygmy blue whales are only small compared to other blue whales; at 90 tons, they can weigh up to 15 elephants, assuming an elephant weighs around 6 tons.) Now that scientists are aware of this new population of blue whales, they can work to protect these vulnerable giants from threats such as ship strikes, entanglement in fishing gear, ocean noise and climate change.

“I think it’s pretty cool that the same system that protects the world from nuclear bombs allows us to find new populations of whales, which in the long run can help us study the health of the marine environment,” Tracey Rogers, marine ecologist and senior author of the study, said.

The nuclear test detection system. The underwater microphones are part of the international surveillance system which ensures “that no nuclear explosion goes unnoticed”. The system is a global network (nearing completion) of 170 seismic stations, 80 radionuclide stations, 60 infrasound stations and 11 hydroacoustic stations in 89 countries around the world. Network data is collected at the headquarters of the Comprehensive Nuclear-Test-Ban Treaty Organization in Vienna, where it is made available for civic and scientific purposes. Japan, for example, uses the data to gain real-time information on underwater earthquakes that precede tsunamis, enabling early warnings that save lives.

To hear the chants of the new blue whale population, Leroy and his team poured nearly two decades of recordings of ocean underwater soundscapes from six different recording sites into the monitoring system.

“At first I noticed a lot of horizontal lines on the spectrogram,” Leroy said. “These lines at particular frequencies reflect a strong signal, so there was a lot of energy there.”

The songs varied between sites depending on the season, suggesting that the whales migrated into the central Indian Ocean, reaching as far east as northern Western Australia and possibly as far north as Sri Lanka. It turns out that the Indian Ocean is home to a greater variety of pygmy blue whales than previously thought.

What do whale songs sound like? The rumblings heard on the recordings shared low frequencies, rhythms and structures characteristic of large whales. The audio patterns repeated themselves and were consistent over years of data, leading researchers to believe the animals were blue whales rather than, say, humpback whales.

“Humpback whales are like jazz singers. They change their songs all the time, ”Rogers said. “Blue whales, on the other hand, are more traditional. They sing very structured and simple songs.

Yet researchers knew that different subspecies of blue whales, including those from the Indian Ocean, sing different songs. Although the vocalizations resembled those of blue whales in general, they differed from all known populations of blue whales.

“Whale songs have been a big part of the acoustic soundscape for 18 to 20 years,” Leroy said. “After going through the data, I was like, ‘Wow, there’s a lot of it, not just a few! That’s why we thought it was a different population.

Scientists named the new population of pygmy blue whales “Chagos” after the Indian Ocean archipelago where they were found.

No one has seen the Chagos whales yet, although that’s not surprising. Blue whale populations are often identified by sound rather than sight due to their reclusive nature. The sound travels far in the water, which makes it well suited for the task of identification. It helps that whale songs can be louder than jet engines and can be heard underwater up to 1,000 miles away.

Indeed, those who designed the International Monitoring System took full advantage of the sound propagation properties of water. That is, the system required significantly fewer hydroacoustic stations than seismic, radionuclide, and infrasound stations. Better yet, the system’s acoustic data is available at short notice.

“You don’t have to wait. It’s kind of magical, ”said Leroy, contrasting the experience with previous research in which the acoustic data it needed from a different system – a system unrelated to nuclear test detection – required a wait. one year.

What happens after a new discovery of a whale population? Although the data has provided insight into the existence and movements of the Chagos, Leroy and his team have many unanswered questions. For example: How many of these whales exist? Are their songs innate or do they learn them from a parent? What precisely are their migratory routes? And perhaps most important: How can humans protect these vulnerable giants from modern threats?

Without temporary protection zones in which sailors are advised to slow down or avoid migration routes, boats can collide and kill or injure whales or produce noise that disrupts their feeding, reproduction and social behavior. The International Whaling Commission, which oversees a global whale entanglement network, also needs up-to-date information on whale habitats as part of its work to free whales that become entangled in nets. fishing. Scientists and environmentalists also use information about whale habitats in their advocacy.

It is perhaps not surprising that the international monitoring system, which was designed to protect all living things on Earth, has already helped the recently discovered blue whales of Chagos. As Leroy said, “Discovering a new population is the first step in protecting it”.

Source link

About John Crowder

Check Also

Bircham’s superb exit leaves Waterford feeling the Blues ahead of play-offs

The August 5 announcement that Marc Bircham had signed a new two-and-a-half-year contract with Waterford …

Leave a Reply

Your email address will not be published. Required fields are marked *