海岸かいがんに打うち上あげられたクジラ4頭よんとうを研究けんきゅう機関きかんが調査ちょうさ 生態せいたい系けい確認かくにんへ

Last month, after four whales were stranded on the coast of Tateyama City, Chiba Prefecture, a whale research organization conducted a field survey at the site on the 5th.

According to investigators, it is rare for two or more whales to wash ashore at the same time, and they plan to use this as an opportunity to study the ecosystem.

On the 29th of last month, about 20 people, including researchers from the Institute of Cetacean Research who study whales, conducted an investigation at Heisaura Beach in Tateyama City, where four whales had washed ashore.

The survey was conducted to study the ecosystem of whales in the seas near Japan. Skin and teeth samples were collected for DNA analysis, and the size and gender of the whales were also checked.

As a result of the investigation, it was found that one of the four was reduced to just bones, but the remaining three were identified as male sperm whales measuring between 12 and 14 meters in length.

According to the investigator, cases where two or more animals are stranded on the shore at the same time are rare.

Mr. Chikara Tamura, counselor at the Japan Cetacean Research Institute, said, Geographically, there have been several confirmed cases of whales washing ashore in this area in the past.

I would like to use this data for whale resource management, he said.

Reports of whales being stranded on beaches and other places have been made from various parts of the country in the past as well.

In addition to a whale, believed to be a juvenile humpback, found on the coast of Kunigami Village, Okinawa Prefecture in February last year, in 2022, the carcass of a whale about six meters long washed ashore on the coast of Odawara City, Kanagawa Prefecture.

In one case where multiple whales were stranded, 14 sperm whales were found on the coast of Kagoshima Prefecture in 2002.

According to the Institute of Cetacean Research in Japan, it was reported that 40 whales were stranded in the country last year, and that an average of about 10 sperm whales wash ashore annually.

Expert: Three conditions applied, and the whales sonar didnt work. Professor Emeritus Hideo Kato of Tokyo University of Marine Science and Technology, who is well-versed in whale ecology, explained the characteristics of whales: Whales sense their surroundings by detecting things that reflect sound back to them.

They say, I make sounds myself and move as I see rocks or cliffs when the sound bounces back.

He listed three conditions that make it easy for whales to become stranded: When the area is shallow, when the seabed is sandy or muddy, and when the geomagnetic contour lines—like the contour lines on a weather map—are nearly perpendicular to the coastline, strandings are very likely to occur, he said.

Specifically, In shallow water, your own sound doesnt really bounce back to you, and with sand, the sound just gets absorbed as it is.

He explained, Even if there are obstacles, they just keep going as if its the sea.

He also pointed out the following about the “contour lines of geomagnetism”: “The general strategy for migratory movement, such as heading all the way to Hokkaido, is to follow the same geomagnetic contour lines, but if the contour lines are perpendicular to the shoreline, I end up advancing further and before I know it, I find myself on land.”

On top of that, “This site also appeared to be shallow, and since all three conditions applied, the whales’ sonar didn’t work very well.”

He explained, The coastline to the north of the current site, such as Kujukuri in Chiba Prefecture, meets all three conditions.