About four out of 10 freshwater fish species in North America are in peril, says a major study by US, Canadian, and Mexican scientists. And the number of subspecies of fish populations in trouble has nearly doubled since 1989, the new report says. One biologist called it "silent extinctions" because few notice the dramatic dwindling deep in lakes, rivers, and streams. And while they are unaware, people are the chief cause of the problem by polluting and damming freshwater habitats, experts said.
In the first massive study of freshwater fish on the continent in 19 years, scientists looked not just at species, but at subspecies—physically distinct populations restricted to certain geographic areas. The scientists found that 700 such fish populations are vulnerable, threatened, or endangered, up from 364 two decades ago. And 457 entire species are in trouble or already extinct.