Conservation of native freshwater fishes in the Mediterranean-type climate of California, USA: A review

Abstract

The native fish fauna of California, like the faunas of other regions of the world with Mediterranean climate, is declining rapidly: 63% of the 115 taxa are extinct or in danger of becoming extinct. The native fishes fall into three major groups: (1) diadromous fishes and their stream-resident derivatives; (2) large, long-lived freshwater dispersant fishes, mostly Cyprinidae; and (3) small freshwater dispersant fishes in isolated inland habitats, such as desert springs. In this respect, the fish fauna of California bears a closer resemblance to the fish fauna of Europe than it does to that of eastern North America. The native fish fauna is in trouble because most of the precipitation occurs in the northern half of the state or at high elevations, while most of the human need for water is in the southern half of the state, at low elevations. The result has been the construction of dams and reservoirs on every major stream in the state and thousands of kilometres of aqueducts. In addition, poor land use has devastated many drainages, introduced fishes have replaced native fishes, and fisheries have depleted some stocks. Major droughts have exacerbated these problems. Most of the extinct or endangered species are either native to small isolated habitats or to big rivers. The fishes have continued to decline despite conservation efforts using such powerful legal tools as the Endangered Species Act, the California Department of Fish and Game Code, and the Public Trust Doctrine. The poor state of California's fish fauna is a strong indication that many other endemic aquatic organisms, much more poorly known than the fishes, are in trouble as well. Protecting fishes will thus help to protect aquatic biodiversity in California. With this in mind, a general plan for protecting California's aquatic biota is presented. The plan has two main components: (1) legal protection for species in immediate danger of extinction and (2) development of a statewide system of protected waters called Aquatic Diversity Management Areas (ADMAs). For the latter component, a framework is presented that consists of (1) criteria for the design of ADMAs; (2) a system for ranking the suitability of aquatic habitats for protection of the native biota; (3) a classification system for California's waters; and (4) a long-term scheme for protecting aquatic biodiversity statewide.