142 



Fishes — Our Living Rfsinirces 



significantly in the immediate future. Therefore, 

 if we are to preserve the diversity and adaptive 

 potential of our fishes, we must understand 

 much more of their ecology. Vague generaliza- 

 tions about habitat requirements or the results of 

 biotic interactions are no lonser enough. We 



must know quantitatively and exactly how fish- 

 es use habitat and how that use changes in the 

 face of biotic pressures. Only when armed with 

 such information are we likely to reduce the 

 cunent trends among our native fishes. 



Imperiled 



Freshwater 



Fishes 



by 

 James E. Johnson 



National Biological Service 



The United States is blessed with perhaps 

 800 species of native freshwater fishes (Lee 

 et al. 1980: Moyle and Cech 1988; Wanen and 

 BuiT 1994). These fishes range from old. primi- 

 tive forms such as paddlefish, bowfin. gar. and 

 sturgeon, to younger, more advanced fishes, 

 such as minnows, darters, and sunfishes. They 

 are not equally distributed across the nation, but 

 tend to concentrate in larger, more diverse envi- 

 ronments such as the Mississippi River drainage 

 (375 species; Robison 1986; Wanen and Buit 

 1994). Drainages that have not undergone 

 recent geological change, such as the Tennessee 

 and Cumberland rivers, are also rich in native 

 freshwater fishes (250 species; Stames and 

 Etnier 1986). Fewer native fishes are found in 

 isolated drainages such as the Colorado River 

 (36 species; Carlson and Muth 1989). More arid 

 states west of the lOOth meridian average about 

 44 native fish species per state, while states east 

 of that boundary average more than three times 

 that amount ( 138 native species; Figure). 



Extinction, dispersal, and evolution are natu- 

 rally occurring processes that influence the 

 kinds and numbers of fishes inhabiting our 

 streams and lakes. More recent human-related 

 impacts to aquatic ecosystems, such as 

 damming of rivers, pumping of aquifers, addi- 

 tion of pollutants, and introductions of 



non-native species, also affect native fishes, but 

 al a more rapid rate than natural processes. 

 Some fishes are better able to withstand these 

 rapid changes to their environments or are able 

 to find temporary refuge in adjacent habitats; 

 fishes that lack tolerance or are unable to retreat 

 face extinction. 



In 1979 the Endangered Species Committee 

 of the American Fisheries Society ( AFS) devel- 

 oped a list of 251 freshwater fishes of North 

 America judged in danger of disappearing 

 (Deacon et al. 1979). 198 of which are found in 

 the United States. A decade later, AFS updated 

 the list (Williams et al. 1989). noting 364 taxa 

 of fishes in some degree of danger, 254 of 

 which are native to the United States. Both AFS 

 lists used the same endangered and threatened 

 categories defined in the Endangered Species 

 Act of 1973. and added a special concern cate- 

 gory to include fishes that could become threat- 

 ened or endangered with relatively minor dis- 

 turbances to their habitat. These imperiled 

 native fishes are the first to indicate changes in 

 our surface waters; thus their status provides us 

 with a method of judging the health of our 

 streams and lakes. This article compares the two 

 AFS data sets to assess the trends in the status 

 of freshwater fishes in the United States over 

 the past decade. 



Figure. Number of fislies consid- 

 ered imperiled and number of 

 native fresliwater fishes of the con- 

 tiguous United States by state 

 (redrawn from Warren and Burr 

 1994). 



