Extinct North American Freshwater Fishes

Extinction is a natural process in nature and is the opposite of speciation—the evolution of new life forms. Importantly, 90%–96% of all species that became extinct over geological time disappeared during the normal give and take of speciation and extinction1. There is widespread evidence that modern rates of extinction in many plants and animals significantly exceed background rates in the fossil record. From 1900 to 2010, 57 species and subspecies of North American freshwater fishes became extinct, and since 1898, three distinct populations of valued fishes were extirpated from the continent2. Intuitively, this number of extinctions seems unnaturally high. Since the first tally of extinct North American fishes in 19893, the number of extinct fishes increased by 25%2,4. From the end of the 19th century to the present, modern extinctions varied by decade but significantly increased after 1950. The post-1950s increase in extinction rates likely corresponds to substantial economic, demographic, and land-use changes that occurred in North America after WWII2.

A meaningful way to evaluate modern extinctions is to compare modern rates of extinction to background rates using data from the fossil record. The mean background extinction rate (from origination to extinction) for freshwater fish species is estimated to be one extinction/3 million years. The modern extinction rate in North American freshwater fishes is conservatively estimated to be 877 times greater than the background rate—for the interval 1900 to 2010. Calculation of modern to background extinction rate (M:BER) is similar to extinctions per million species years (E/MSY) but differs in that actual background extinction rates are used in lieu of one extinction/million years.) M:BER ratios fluctuate by year because total North American fishes increases each year due to descriptions of new species and because extinctions are intermittent (the last one occurred in 2006). The M:BER value for North American freshwater fishes in 2012=863 and will continue to decline annually until the next extinction occurs. During the 20th century, freshwater fishes had the highest extinction rate among all vertebrates worldwide. Low numbers of fish extinctions documented from other continents suggests that extinctions are under-reported in Africa, Eurasia, and South America at this time. It is estimated that future extinctions in North America will increase from 39 currently extinct fish species to between 53 and 86 species by 2050.