Migratory freshwater fish populations are in freefall and risk collapse, according to a major UN assessment. The report warns of habitat destruction, overfishing, and water pollution threatening the survival of hundreds of species. Some species, including the Chinese paddlefish, have already been declared extinct and others are dependent on captive breeding stock and reintroductions to support wild populations. Conservation group WWF has reported an 81 percent decrease in migratory freshwater numbers since 1970. The assessment by the Convention on the Conservation of Migratory Species of Wild Animals identifies nearly 350 migratory fish species that could benefit from greater protection.