Whale deaths in Japan's Osaka Bay spark concern about cause and frequency: 'internal Google maps are messed up'
Marine biologists are trying to determine why whales are swimming into the enclave of Osaka Bay, where they are becoming disoriented and stressed before apparently starving to death.
A sperm whale detected in mid-January in the bay - an area busy with shipping - was on February 18 confirmed to have died, although it is not clear why the marine mammal had strayed into the shallow and congested waters off Japan's second city.
The whale was the third to die in the area in consecutive years, with experts concerned that such deaths may become more frequent.
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Researchers suggest a combination of factors may have contributed to the death of the 14-metre whale, which weighed more than 25 tons.
"The warm Kuroshio Current that flows outside Osaka Bay and along the east coast of Japan is extremely strong, and it may well be that this individual entered the bay by mistake instead of continuing to the north," said Mari Kobayashi, head of the marine biology laboratory at the Hokkaido-Okhotsk campus of Tokyo University of Agriculture.
"The bay is very shallow and this species of whale uses sound waves to navigate, but the narrow area of the bay would have made navigating very difficult and left it disoriented," she told This Week in Asia.
The area immediately off Osaka is a maze of narrow channels constructed between man-made islands, with the whale's carcass located in a channel that ended in a port facility.
"As well as being confused, the bay does not have enough food to sustain a whale, and it is likely this one starved," Kobayashi added.
Kevin Short, a naturalist and former professor of cultural anthropology at Tokyo University of Information Sciences, suggested that global warming was affecting deep sea currents and raising the temperature of water within Osaka Bay, which might be attracting marine life that might not have previously ventured into the area, including whales, dolphins and turtles.
"And when that happens and they wind up in the wrong place, then their internal 'Google Earth' maps are messed up, they cannot echolocate their positions, and they cannot find their way back to deep water," he said, adding that the whales' confusion was likely to be worsened by the noises generated by maritime traffic in the bay.
"Quite soon they starve, or possibly they are ill," Short added.
Pollution in the bay did not appear to have been a contributing factor, Short said, although prefectural officials had been carrying out tests on the carcass after it was retrieved from the water to determine the cause of death.
The whale was buried at an industrial waste disposal site and will be exhumed in about two years to be preserved and used as a skeletal specimen in a museum in the city.
Kobayashi says there appears to be little that can be done to prevent whales from entering Osaka Bay in the future, with experts reporting hundreds of similar beachings or strandings of whales or dolphins around the country every year.
Short adds, however, that the whale's death is not a serious environmental concern as the sperm whale population has rebounded in recent years after being close to extinction. Japan stopped hunting sperm whales in 1988.
This article originally appeared on the South China Morning Post (SCMP).
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