Sapporo - Former residents of Russian-held northwestern Pacific islands claimed by Japan will hold memorial services for their ancestors at sea and in the air between July 25 and Nov. 7, the prefectural government of Hokkaido said Friday.The events will take place as exchange programs have been suspended due to Russia’s invasion of Ukraine. The islands are collectively called the Northern Territories in Japan.A memorial service at sea will be held for the fifth consecutive year since Russia began its invasion in 2022. This year, an aerial memorial service is planned in consideration of the physical burden on former residents, whose average age is over 90.