Migratory freshwater fish populations ‘down by more than 80% since 1970’

A salmon swimming upstream to spawn on the River Tyne in Northumberland. There are 1.2m barriers such as weirs and dams blocking fish migration in Europe. Photograph: O Humphreys/PA

Migratory fish populations have crashed by more than 80% since 1970, new findings show.

Populations are declining in all regions of the world, but it is happening fastest in South America and the Caribbean, where abundance of these species has dropped by 91% over the past 50 years.