Over 400 endangered horseshoe crabs found dead in Fukuoka Pref.

KITAKYUSHU, Fukuoka -- Over 400 endangered horseshoe crabs have been found dead in the Sone tidal flats here this year, with rising ocean temperatures due to hot weather suspected as the cause.

Normally only 50 to 60 horseshoe crabs are found dead a year. According to Shungo Takahashi, head of the Fukuoka branch of "Nihon Kabutogani o Mamoru Kai" (association to protect the Japanese horseshoe crab), many of the dead horseshoe crabs that have washed up on the shore are young, so the large number of deaths cannot be explained as the result of dying from old age.

In 2004, around 300 of the crabs died, and the cause of those deaths is also unknown. This year's deaths are the first large die-off since then.

Satoko Seino, associate professor of ecological engineering at Kyushu University's Graduate School of Engineering, who studies the horseshoe crabs off the coast of Fukuoka Prefecture, says, "It is possible that the deaths were caused by a lack of oxygen at the sea floor due to the combination of a lack of ocean water stirring by typhoons and a rise in ocean temperatures caused by continuing hot weather."

According to the Fukuoka Fisheries and Marine Technology Research Center's Buzen Sea lab, the temperature of the Buzen Sea off of the tidal flats from May through August this year was between 0.9 and 1.6 degrees Celsius higher than in a typical year.

Around 2,000 horseshoe crabs are estimated to live in the Sone tidal flats, Japan's largest habitat for the crab. Takahashi says, "It is possible the environment in the coastal waters is changing. I want an investigation to uncover the precise causes (of the deaths.)"