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150 Conservation of Stream Fishes stricted to North America and the suckers (Catostomi- dae) nearly so. Smaller families also confined to North America are pirate perch (Aphredoderidae), trout- perches (Percopsidae), and cavefishes (Amblyopsidae). Darters (Etheostomatini, Percidae) have radiated spec- tacularly (Page 1983); they contribute about 20% of the species in the total fish fauna north of Mexico and are among the most attractive of all fishes. The cyprinid genus Notropis (which may be polyphyletic) is similarly diverse. Gilbert (1976) and Hocutt & Wiley ( 1986) pro- vide thorough treatments of the origin and distribution of North American fishes. Moyle and Cech (1982) illus- trate representatives of most families and summarize their biology. Minnows dominate the fauna and the Percidae (mostly darters) run a close second in diversity. Other prominent families are the suckers, catfishes, and sun- fishes. Killifishes (Cyprinodontidae) and live bearers (Poeciliidae) are widely distributed and are especially characteristic of remnant waters of the southwestern United States (see Vrijenhoek & Meffe, this issue). Salmonidae (trout, salmon, whitefish, grayling) and sculpins become increasingly common in the northern United States and Canada. Approximately twenty addi- tional families contribute species, many of which are widespread and numerous. These fishes are not evenly distributed (Fig. I). Rivers west of the continental divide contain relatively few species although their faunas are distinctive and ende- mism is high (e.g., Stanford & Ward 1986). East of the divide, the Mississippi system is far richer than the smaller Gulf and Atlantic coastal rivers although these in turn have more species than the Pacific drainages. Fish diversity is greatest in the southeastern United States (see McAllister et al. [1986] for a quantitative analysis of patterns of species richness). Diversity decreases north- ward, especially along the Atlantic coast. Rivers such as the Savannah that drain physiographically diverse areas have more species than rivers such as the St. Johns in Florida that are confined to lowlands. The Great lakes and tributaries, which are not con- sidered further in this essay, have 162 native species (Underhill 1986). Most of these occur in streams. The lacustrine component of the fish fauna has been cata- strophically altered by introductions, exploitation, and pollution ( e.g., Smith 1968; Crowder 1980), resulting in the extinction of three species and one subspecies (Williams & Nowak 1986). . Conservation Status More than half of the freshwater fishes of the United States and Canada receive some legal protection in at least part of their range Oohnson 1987). Far fewer (a total of 75 species and subspecies) are federally desig- Conservation Biology Volume 2, No. 2,}une 1988 Sheldon nated as endangered or threatened (U.S. Fish & Wildlife Service 1987). Endangered taxa are strongly concen- trated in the arid west (Fig. 2). Threatened species (Fig. 3) likewise are predominantly western but include a greater proportion from the diverse southeastern fauna. Many of these fishes, especially the western ones, are extremely localized in springs and fragmented desert drainages. Ono et al. (1983) provide species accounts for these and additional rare species. The emphasis in the conservation of fishes has been on habitat preservation and single-species management. Given the restricted habitats of many fishes and the eco- nomic value of water in arid landscapes, this emphasis is understandable and sensible. Focused plans for the man- agement of species and habitats will continue to be an integral part of fish conservation. However, I suggest that a comprehensive view of river systems and their fishes is required if more than a small fraction of the fish fauna is to persist. Patterns of Distribution and Abundance Few species of stream fish are widely distributed (McAl- lister et al. 1986). Abundances in local assemblages ap- proximate lognormal frequency distributions (Loubens 1970; Sheldon 1987). Thus, most species are geograph- ically restricted and numerically rare where they occur. Furthermore, patchy distributions are common. Some threatened species (Fig. 3) apparently exist in only a few widely separated localities. Although this apparent patchiness may be a consequence of general rarity and low detectability (e.g., Starnes et al. 1977), present ev- idence implies both local rarity and restricted range. Historical records are adequate to show substantial declines of many stream fishes. For example, the rosy- face shiner, Notropis rubellus, remains widely distrib- uted (Lee et al. 1980) and locally common, yet it had disappeared from much of its range in Ohio by midcen- tury (Trautman 1957). A more extreme case is the hare- lip sucker Lagochila, which vanished from the rivers of nine southeastern and midwestem states before 1900 (Ono et al. 1983). Rivers as Islands Species-area relationships and problems of connected- ness occupy a prominent place in conservation theory, and stream systems are amenable to this approach. The geometry of drainage area has been related to species richness of fishes (Eadie et al. 1986; Larsen et al. 1986; Swift et al. 1986) and molluscs (Sepkoski & Rex 1974). Discharge, a more direct measure of available stream habitat, was used by Livingstone, . Rowland, & Bailey (1982) and Sheldon (1987) in place of area. The ob- served increase of faunal diversity with increasing drain-