The percentage of foreign fish in rivers is strongly linked to nearby economic activity, according to a new study of 1,055 river basins worldwide. Nonnative plants and animals can outcompete local species and damage ecosystems, sometimes to the point of collapse.
Freshwater fish can’t readily move from one river basin to another on their own, so the distribution of invasive fish ought to reflect human influence, says lead researcher Sébastien Brosse of the Laboratory of Evolution and Biological Diversity in Toulouse, France. Local measures of economic activity, such as gross domestic product, account for about 70 percent of the distribution of foreign fish, supporting the idea that human activity is largely to blame, Brosse’s team reports in the February PLoS Biology. Red indicates greater than 25 percent invasive fish; orange, 5 to 25 percent; and yellow, less than 5 percent.