Visitors to the Yuigahama beach in Kamakura, Kanagawa Prefecture, gaze at the dead blue whale calf that washed ashore in August 2018. (Asahi Shimbun file photo)

It's not everyday that a blue whale washes ashore in Japan, so when one did researchers seized on the opportunity to determine how the member of the largest animal species in existence lived and died.

The beaching nine months ago in Kamakura, Kanagawa Prefecture, was exceptionally rare, being the only time the endangered species has done so in local waters.

The dead whale calf measured about 10 meters. An adult blue whale can reach lengths of 21 to 26 meters.

Local authorities initially pondered how to dispose of the carcass that stunned summer visitors to the Yuigahama beach in August 2018, but Yuko Tajima, a curator at the National Museum of Nature and Science who is an expert on marine mammalogy, insisted on an autopsy.

The first confirmed arrival of a blue whale on Japanese shores provided a precious opportunity for researchers to directly study the biology of the animal.

Scientists determined the calf was male and only a few months old. Although the calf likely died at sea before washing ashore, it was not clear how that happened as there were no visible signs of injury or disease.

Ayaka Matsuda, a post-doctorate researcher affiliated with the Japan Society for the Promotion of Science, was among those who studied the whale.

To ascertain where the calf came from, Matsuda looked into the ratio of the radionuclide carbon-14 used in radiocarbon dating that was found in the baleen plate that whales use as a filter to gather food.

She found strong evidence that the animal inhabited waters in the Oyashio current that originates in the Arctic Ocean and flows southward along the Chishima island chain into the northern Pacific.

Based on the finding, Matsuda said it seemed likely the calf had lived off the coast of Iwate Prefecture and in waters further north.

COMPARING GENETIC INFORMATION

Shin Nishida, an associate professor of biology at the University of Miyazaki in Kyushu, analyzed genetic information found in cells taken from the whale.

Researchers in other countries have already collected genetic information of blue whales found off the west coasts of North and South America as well as the Indian and Antarctic Oceans.

A comparison found that the baby whale was in a group similar to blue whales that inhabit waters off the West Coast of North America.

"We will probably be able to specify in more detail the genetic characteristics of blue whales that approach Japan if we can continue to accumulate such data," Nishida said.

Other researchers were concerned that the blue whale had not even survived a year.

Mari Ochiai, a specially appointed assistant professor of environmental chemistry at Ehime University, discovered traces of the toxic insecticide DDT as well as polychlorinated biphenyl (PCB), another toxin, in the fatty skin and liver of the calf.

Most nations now ban the production and use of those chemicals, but the levels found were similar to that found in blue whales off the coast of California.

"It likely was transmitted from the ecosystem to the next generation through mother's milk, so there are concerns that the effects of chemical pollution may last longer than previously thought," Ochiai said.

300 WHALES BEACHED ANNUALLY

While the beaching was the first by a blue whale in Japan, roughly 300 whales of other types, as well as dolphins, wash ashore every year.

Usually it is because the animals are sick or got lost pursuing food sources in the ocean.

Tajima said that the cause of death is only determined in about 20 percent of cases.

While it is still unclear what effect pollutants such as DDT and PCB had, researchers have determined that high levels of pollutants found in finless porpoises captured in Japanese waters often led to a high incidence of parasites in the lungs of such animals.

"If the beaching was some form of warning from the whales, it is the obligation of humans to determine how those animals lived and how they died," Tajima said.

The results of research into the blue whale will be displayed at a special exhibition titled "Mammals 2--Struggle for Life" being held at the National Museum of Nature and Science in Tokyo's Ueno district until June 16.

For more information in English about the exhibition go to the website at ( http://www.kahaku.go.jp/english/exhibitions/ueno/special/2019/mammal2/ ).