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Warming oceans may be behind spread of 'killer' octopus in Sea of Japan

MIYAZU, Kyoto -- Tiny and highly venomous blue-ringed octopi have begun showing up along the Sea of Japan coast in recent years in another possible sign of the effects of global warming.

    The blue-ringed octopus, which turns yellow and enhances its eponymous stripes when threatened, is only about 10 centimeters in size, but its saliva contains tetrodotoxin -- the same neurotoxin found in fugu puffer fish. Being bit by one can cause respiratory failure, and there have been fatal encounters with the diminutive creatures recorded in Australia and other areas.

    A blue-ringed octopus is seen in its calm state, with coloration that allows it to blend in with rocks or coral, in Miyazu, Kyoto Prefecture. (Mainichi)
    A blue-ringed octopus is seen after being threatened, in Miyazu, Kyoto Prefecture. Note the brighter yellow and more defined stripes on its skin. (Mainichi)

    Blue-ringed octopi are native to tropical and subtropical waters of the western Pacific, and have been seen in the warmer waters of Japan's own Pacific coast, including those off Wakayama Prefecture. However, they are increasingly also being seen in the Sea of Japan, near the Oki Islands in Shimane Prefecture and off the coast of Tottori Prefecture.

    Researchers at the Kyoto Prefectural Agriculture, Forestry and Fisheries Technology Center are working to establish where and how the octopi are gaining their foothold, though higher ocean temperatures may have allowed the animals to spread north from their traditional habitat.

    It is thought that warm ocean currents carried the octopi north into Japanese waters. They have increasingly been captured in the Pacific waters off the Kanto region. In recent years, they have been spotted in the Sea of Japan off northern Kyushu and western Honshu. Since 2009, they have also been found further north in the sea off Fukui and Kyoto prefectures once every few years. According to the Kyoto fisheries technology center, seven of the cephalopods have been reported in the prefecture since autumn last year, with witnesses saying they saw octopi crawling along rocky underwater surfaces. The center believes that the water in the area may now be warm enough year-round for the animals to winter in local inlets.

    A local fisherman brought one specimen caught in a box net to an aquarium in the Odashukuno district of Miyazu, Kyoto Prefecture, in September last year. Several other blue-ringed octopi were later captured as well, and there were reports that some were octopus babies measuring less than 2 centimeters long.

    "The sea temperature is going up, and the types of fish I can catch are changing," a 54-year-old fisherman who had caught four of the octopi as of January this year said. "Perhaps the blue-ringed octopi that have come up from the south can stay here the whole winter now."

    Apparently no one along the Kyoto or Fukui coast has yet been injured by one of the venomous animals, but concerns remain as some areas there are popular with swimmers during the summer.

    "At the very least, no matter how cute they (the blue-ringed octopi) are, please don't touch them," commented Kyoto fisheries technology center chief researcher Yoichiro Ueno.

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