This summer coastal towns in Japan were visited by an unusual number of sharks, mostly of the shy hammerhead variety. Reports vary but a school of up to thirty hammerheads was spotted off the coast in relatively shallow water. The sharks were tracked from the sea and air by the Coast Guard and showed no signs of interest in humans as they moved down the east coast into two bays just a few hours drive South of Tokyo. While individual sightings are not uncommon to these areas the prolonged and increased presence of the visitors caused authorities to raise the alarm and close beaches in some towns. As luck would have it, the closures occurred during the four-day national holiday period of Obon, taking a bite out of local tourism. General consensus is that the sharks were drawn to the coastal waters due to changing migratory patterns of fish lower down in the food chain, in turn caused by a change in the temperature and path of the Kuro-Shiro current that runs along almost the entire length of Japan’s lower coast in the North Pacific Ocean and transports warm tropical water to the polar regions. Compared to Australia, which has recently seen an unprecedented – and so far, inexplicable - spike in shark attacks, South Africa and the US, the number of incidents involving humans and sharks is almost negligible in Japan. Hammerhead sharks are mostly harmless to humans, with only 3 of the 9 species linked to incidents involving people. They are found worldwide in tropic and sub tropic waters, preferring to live in deeper areas. Due to their large fin size they are targeted by fisheries and the (mostly illegal) fin trade, but also fall victim to the indiscriminate practice of long-lining. In 2013 CITES (Convention on International Trade in Endangered Species) recognised 3 species as endangered and passed laws regulating their trade. On a personal level, I am a lot more conscious of the dangers of jellyfish. I have been stung three times this year: once in Perth, Western Australia and twice in Hayama, Japan. While not very painful, the stings drape me in unsightly welts that itch for days. Compared to a shark-bite the discomfort is insignificant of course. On my trip to Australia’s Gold Coast last month I was aware of the usual possibility of sharks in the area, but with a life guard station every several hundred metres I felt relatively at ease. What did worry me was seeing several dead ‘blue-bottle’ jellyfish that had been washed up on beach. A single painful touch from a blue-bottle years ago forced me to leave the water and seek medical attention as my entire arm went numb, breathing became laboured as I went into mild (but intensely experienced) anaphylactic shock. Of all the numerous varieties of jellyfish I am wary of these little creatures the most! The bad news is that recently there has been a dramatic increase in the number of jellyfish around the world. Globally, the warming of our seas through the absorption of carbon dioxide is resulting in ocean acidification. The higher acidity reduces the amount of oxygen in the water. In addition to growing coastal development and overfishing, the decrease in oxygen means that there are now fewer, and smaller, fish alive to feed on jellyfish resulting in “explosive population growth” which has recently been the cause of crises around the globe. In 2013 seawater vents used to cool a Swedish nuclear reactor became so clogged up with jellyfish that the plant had to be temporarily shut down. A year before that, in Japan a thermal power plant went offline until the creatures were removed from the water around the cooling vents. And recently the French Riviera has become so inundated that tourists now pay more attention to jellyfish warnings than weather advisories The increased numbers are effecting recreation and economies worldwide. Growing up in Cape Town’s False Bay I was lucky to be surrounded by a community of surfers, divers and other water people who were educated about sharks and had balanced attitudes towards these apex predators. But on the whole, we humans still have a lot of work ahead when it comes to understanding the oceans, the creatures in them, and how to live with them. Sharks have been around for about 400 million years and have survived at least 5 ice-ages as well as the extinction of the dinosaurs; but jellyfish are the oldest multi-organ creature known and are at least 500 million years old. As climate and ocean conditions continue to change I have a feeling we will need to learn more about jellyfish quite soon. Sources: www.sharks-world.com/hammerhead_shark/ asia.nikkei.com/magazine/20150205-Changes-in-the-air/Tech-Science/World-worries-as-jellyfish-swarms-swell www.japantoday.com/category/national/view/shark-sightings-continue-at-beaches
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