150 



Fishes — Our Living Kc.wiiiivcs 



Aspen/ 



< Colorado 



Figure. Colorado River Basin. 



reductions that include decreased abundance in 

 all or part of their ranges, overall range reduc- 

 tions, or virtual or actual extinctions (Tables 1 

 and 2). Presently, 40 of the 49 strictly freshwa- 

 ter, native species are considered either possibly 

 or actually jeopardized or are extinct (Table 1 ). 

 Of the 40, 1 2 are of special concern, 25 are con- 

 sidered endangered or threatened, and 3 are 

 believed extinct. 



In the Lower Basin, only 3 of the 10 native 

 species that inhabited the mainstem of the lower 

 Colorado River remained by the 1940's but by 

 the 1960"s, none remained. In the lower Salt 

 River portion of the Gila River system, the orig- 

 inal complement of 14 taxa was also reduced to 

 3 by the 1940"s and to 2 by the 1960"s: today, 

 they are probably extirpated. In the early 

 1900's, the isolated springs of the Pluvial White 

 River system in southern Nevada harbored 1 7 

 endemic taxa; today, 1 of those taxa is extinct, 9 

 endangered, 3 threatened, and the remainder of 



Table 1. N,itive fish taxa of the Colorado River Basin 

 including currently recognized subspecies. Taxa denoted 

 by * may eventually prove genetically distinct from popu- 

 lations outside the Colorado River Basin. Those denoted 

 "(ni)" are marine invaders. Status of jeopardized and 

 extinct species appears in parentheses: E = endangered; 

 T = threatened; SC = special concern; X = extinct (based, 

 in part, on Carlson and Muth 1989; Williams et al. 1989; 

 and the National Biological Service's Category 2 list). 

 Common names bracketed with quotation marks indicate 

 that those species are undescribed and not officially 

 named. 



