Oct 19

Scientists have increased their estimate of the number of humpback whales in the North Pacific Ocean, according to a report published in the journal Marine Mammal Science.

Photo of humpback whales, two adults breaching

The revised estimate follows analysis of data compiled in 2008 as part of the largest survey ever undertaken to assess humpback whale populations in the North Pacific.

Photographic survey

The original study, known as the ‘Structure of Populations, Levels of Abundance and Status of Humpbacks’ (SPLASH), was a three-year project involving scientists from a number of different countries. The project used photographs to determine whale numbers, relying on the unique fluke patterns of the whales to identify individuals.

By matching photos from the species’ northern feeding grounds around the Pacific Rim with photographs of the same individuals in the warm tropical waters of their southern feeding grounds, the scientists were able to produce an estimate of the overall humpback whale population.

Photo of humpback whale fluke

The pattern of pigmentation on a humpback whale’s tail fluke is unique and can be used like a ‘fingerprint’ to identify individuals

The 2008 study originally estimated humpback whale numbers in the North Pacific at just under 20,000 individuals, based on a preliminary examination of the data. However, the new report indicates the population to be over 21,000, or possibly even higher.

According to Dr Jay Barlow, a researcher at the NOAA Southwest Fisheries Science Center in La Jolla, California, “These improved numbers are encouraging… We feel the numbers may even be larger since there have been across-the-board increases in known population areas and unknown areas have probably seen the same increases.”

Photo of humpback whale swimming

Humpback whale recovery

One of the major targets of the whaling industry, the humpback whale population was decimated by commercial whaling during the 20th century. However, the new population estimate shows a significant improvement on the 1,400 individuals recorded at the end of commercial whaling in 1966.

Although the humpback whale is still vulnerable to a range of threats, including marine pollution and climate change, these figures give encouraging evidence that the species is recovering from overexploitation.

Photo of a pair of humpback whales with extended throat pleats

This latest revision to the study provides an accurate estimate for humpback whales in an entire ocean that could not have been possible without researchers working together to pool data,” said John Calambokidis, one of the founders of Cascadia Research.

While populations of some other whale species remain very low, this shows that humpback whales are among those that have recovered strongly from whaling.”

View the original Marine Mammal Science article.

Read more on this story at Eurekalert – New, higher estimates of endangered humpback whales in the North Pacific.

View photos and videos of the humpback whale on ARKive.

Liz Shaw, ARKive Species Text Author

Mar 15

A new study by scientists at the University of St Andrews has found that beaked whales are particularly sensitive to unusual sounds, such as sonar.

Photo of a Blainville's beaked whale breaching

Blainville's beaked whale breaching

Sonar linked to whale strandings

The use of sonar for naval communication has been linked to beaked whales stranding in the past, with concerns that the whale deaths may be directly linked to the mid-frequency signals.

Strandings along the coast are thought to occur when whales become disorientated and are unable to follow their usual routes.

Working with some of the world’s marine experts, the scientists investigated how sonar affected beaked whales in the Bahamas. They monitored the reaction of Blainville’s beaked whales (Mesoplodon densirostris) to both simulated sonar calls and live sonar calls during naval exercises in the area.

The researchers were able to listen to the group of whales using underwater microphones, called hydrophones, and electronic tags attached to the whales allowed the team to track the whales’ movements using satellites.

Loud noises disrupt whales’ behaviour

The scientists discovered that sonar caused the whales to stop making the clicking and buzzing calls which they use to navigate and communicate. The whales also ceased foraging and moved quickly away from the loud noises.

Photo of an adult male Blainville’s beaked whale

Adult male Blainville’s beaked whale

According to David Moretti, Principal Investigator for the U.S. Navy, the results indicate that “the animals prematurely stop vocalisations during a deep foraging dive when exposed to sonar. They then ascend slowly and move away from the source, but they do resume foraging dives once they are farther away.”

Although beaked whales are known to emit high-frequency calls, this study is the first to show the whales also react to mid-frequency sounds.

Professor Ian Boyd, chief scientist on the research project, says “We showed that the animals reacted to the sonar sound at much lower levels than had previously been assumed to be the case. We now think that, in some unusual circumstances, they are just unable to get out of the way and this ends up with the animals stranding and dying.

Photo of a biologist performing a post mortem on a Sowerby’s beaked whale

A biologist performing a post mortem on a Sowerby’s beaked whale, one of the most common species to become stranded around the British coast.

Sensitivity of marine mammals to noise may have far-reaching implications

Perhaps one of the most important findings of this new research is the discovery that beaked whales are scared by virtually anything unusual. This may have wider implications for the marine environment, with offshore wind farms, oil rigs and passing ships potentially posing further threats to marine mammals.

Professor Boyd indicates that these other sounds may be more dangerous than sonar as they can be heard constantly, possibly affecting the feeding and reproductive cycles of marine mammals such as whales.

Read the full study, published in the journal PLoS One.

Find out more about beaked whales on ARKive.

Helen Roddis, ARKive Species Text Author

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