Local fisheries cooperative employees check damages to short-spined sea urchins in Nemuro, Hokkaido. (Mainichi/Hiroaki Homma)

       The Mainichi Shimbun answers some common questions readers may have about the mass death of sea urchins and salmon along the coast of the northernmost Japan prefecture of Hokkaido.

       Question: I hear that Hokkaido is suffering record damage to fisheries apparently caused by red tide. How bad is the damage?

       Answer: The mass deaths of marine creatures such as sea urchins and salmon have been confirmed since late September, and the cost is estimated at some 8 billion yen (about $71 million) as of the end of October. Catches have plummeted along the Pacific Ocean coast -- from eastern Hokkaido, where the port city of Kushiro is located, to the central part of the prefecture.

       Q: That's a huge amount of damage. Were there any similar cases in the past?

       A: According to sources including the Japan Fisheries Agency (JFA)'s Seto Inland Sea Fisheries Management Office, as far as records are available, a large number of yellowtail farmed in the Seto Inland Sea in west Japan died from red tide in 1972, causing over 7.1 billion yen (about $63 million) in damage. Though red tide did occur along the coast of Hakodate in southwest Hokkaido in 2015, there have not been many red tide cases in east Japan except for in Tokyo Bay, and the JFA does not compile the extent of damage across the country. For that reason alone, the latest phenomenon can be viewed as rare. The Hokkaido Prefectural Government has said that damage this time could cost as much as 17 billion yen (roughly $150 million).

       Q: What causes red tide?

       A: The presence of Karenia selliformis, a type of phytoplankton that can propagate even under low water temperatures, has been pointed out as a cause of red tide. This plankton is said to have caused red tide in the waters off the southern Kamchatka Peninsula of Russia last year, and it has also been found in waters off the Hokkaido coast damaged this time. Research by Hokkaido University's School of Fisheries Sciences found that, "While it is unclear where the source of the breakout is, it can be thought that the plankton moved southward on the Oyashio Current from Russian waters."

       Q: Does it affect our dinner tables?

       A: Hanamaru Inc., which operates conveyor-belt sushi and other seafood restaurants in Hokkaido and Tokyo, apparently stopped serving sea urchin in early October because their cost price had more than doubled. As it is still unclear when the red tide problem will ease, it will likely take a long time before we can all once again eat sea urchins caught in Hokkaido.

       (Japanese original by Junji Takayama, Hokkaido News Department)

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