The fish fauna and fisheries of the Sierra Nevada have changed dramatically since the massive influx of Euro-Americans began in 1850. Four broad patterns are evident: (1) Anadromous fishes, especially chinook salmon, have been excluded from most of the riverine habitat they once used on the west side of the range; (2) Most resident native fishes have declined in abundance, and the aquatic communities of which they are part have become fragmented, although a few species have had their ranges greatly expanded; (3) Thirty species of non-native fishes have been introduced into or have invaded most waters of the range; (4) Sierra Nevada fisheries have largely shifted from native fishes, especially salmon and other migratory fishes, to introduced fishes. One reflection of these patterns is that of the 40 fishes native to the Sierra Nevada, 6 (15%) are formally listed by the federal and/or state government as threatened or endangered species, 12 (30%) are considered to be species of special concern because they are in trouble statewide and are potential candidates for listing or because they have limited distributions, 4 (10%) are in decline in the Sierra Nevada but are probably in less trouble elsewhere, and 18 (45%) seem to have stable or expanding populations. Among the species that have largely disappeared from the mountain range are chinook salmon, steelhead, and five kinds of native trout. A similar pattern of loss exists for the amphibians of the range.
The decline of native fish and amphibians in the Sierra Nevada is associated with a decline in their habitats. When the biological health of 100 Sierra Nevada watersheds was evaluated, it was found that the biological communities of only seven of the watersheds were in excellent condition, 36 were in good to very good condition, 48 were in fair condition, and nine were in poor condition. The chief factors contributing to poor health were large dams and introduced fishes. However, factors affecting local stream habitats, especially roads and activities associated with roads, were also important. All watersheds in the Sierra Nevada have experienced at least some loss of biotic integrity through the loss or decline of native organisms, but many have considerable potential for recovery. Other watersheds have been permanently altered through the loss of salmon runs, native fish communities, and native frogs.
Reversing the downward trend in aquatic ecosystem health requires appropriate, systematic management of watersheds throughout the range. Assuming maintenance of some set of the native biota is desirable, a number of options for watershed management are possible, ranging from biodiversity-oriented management of all watersheds to simply reacting to the need to keep species from going extinct. A middle ground between these extremes is to designate some watersheds as Aquatic Diversity Management Areas (ADMAs), where the first goal of management is protection of aquatic biodiversity. Forty-two watersheds were recommended as ADMAs on the basis of size (>50 km2), natural hydrologic regime, presence of native fish and amphibians, and representativeness. To achieve more complete protection of aquatic biodiversity, a series of small reserves (Significant Natural Areas) should also be established to protect special or unique habitats.
Related SNEP chapters:
Jennings, M. R. Status of amphibians. Vol. 2, chapter 31, pp. 921-924.
Moyle, P. B. Status of aquatic habitat types. Vol. 2, chapter 32, pp. 945-952.
Moyle, P. B., R. M. Yoshiyama, and R. A. Knapp. Status of fish and fisheries. Vol. 2, chapter 33, pp. 953-973.
Moyle, P. B. and P. J. Randall. Biotic integrity of watersheds. Vol. 2, chapter 34, pp. 975-985.
Erman, N. A. Status of aquatic invertebrates. Vol. 2, chapter 35, pp. 987-1008.
Moyle, P. B. Potential aquatic diversity management areas. Vol. 2, chapter 57, pp. 1493-1503.
Yoshiyama, R. M., E. R. Gerstung, F. W. Fisher, and P. B. Moyle. Historical and present distribution of chinook salmon in the Central Valley drainage of California. Vol. 3, chapter 7, pp. 309-362.
Knapp, R. A. Non-native trout in natural lakes of the Sierra Nevada. Vol. 3, chapter 8, pp. 363-408.
Moyle, P. B., P. J. Randall, and R. M. Yoshiyama. Potential aquatic diversity management areas of the Sierra Nevada. Vol. 3, chapter 9, pp. 409-478.
