Remains of five threatened gray whales were found on the shoreline in Russia's most northeasterly region, a marine life organization said Tuesday. Marine Mammal Council deputy head Andrei Boltunov said the remains were those of gray whales in the Chukotka-California population, which is on Russia's Red List of threatened species, RIA Novosti reported. "We need to register all the cases of these animals' death and investigate the reasons of the incident," Boltunov said. During an aerial survey in September, Russian scientists found the remains of 10 gray whales washed onshore along the 500-mile stretch of the Chukotka coast. RIA Novosti said a cause of death hasn't been determined so far.