PORTLAND, Ore. (Reuters) - Unseasonably hot water has killed nearly half of the sockeye salmon migrating up the Columbia River through Oregon and Washington state, a wildlife official said on Monday. Only 272,000 out of the more than 507,000 sockeye salmon that have swum between two dams along a stretch of the lower Columbia River have survived the journey, said Oregon Department of Fish and Wildlife fisheries manager John North.