Normally C17, I would jump in and say given the close proximity (relatively) to the Yellow Sea, that is probably why, but Osaka Bay is on the oposite side of Japan, and it would be hard for water or dust to get over there. Then again, maybe it isnt.

'The' Yellow Sea is so called because -

"The Yellow Sea is the name given to the northern part of the East China Sea, which is a marginal sea of the Pacific Ocean. It is located between mainland China and the Korean Peninsula. Its name comes from the sand particles from Gobi Desert sand storms that turn the surface of the water golden yellow.

The innermost bay of the Yellow Sea is called the Bohai Sea (previously Pechihli Bay or Chihli Bay). Into it flow both the Yellow River (through Shandong province and its capital Jinan) and Hai He (through Beijing and Tianjin). Deposits of sand and silt from those rivers contribute to the sea color." - wiki.

Doesnt explain the massive sardine die off just a few bays up either.

Suspect they are linked?