However, in February, 2006, Professor Katsumi TSUKAMOTO and others at the Ocean Research Institute, at Tokyo University, almost fully ascertained the spawning ground of Japanese eels to be the area around the Suruga Bank within the Mariana Oceanic Ridge, which is located in the offshore area to the west of Guam and the Mariana Islands.
しかし、2006年2月、東京大学海洋研究所の塚本勝巳教授などが、ニホンウナギの産卵場所がグアム島やマリアナ諸島の西側沖のマリアナ海嶺のスルガ海山付近であることを、ほぼ突き止めた。