The scientists said the situation may be even bleaker than it seemed, as many declines began before 1970. Populations of sturgeon in the Great Lakes of North America, for example, have dropped by 95% from historic levels. Furthermore, suitable data has not been gathered on species in some of the world’s most biodiverse rivers such as the Mekong, Congo, Amazon and Yangtze, where researchers fear there will be hundreds of fish extinctions in the coming decades.