Biodiversity Loss in the Temperate Zone: Decline of the Native Fish Fauna of California

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AbstractIn proportion to the entire fauna, loss of species may be as great in temperate regions as in tropical regions. To test the validity of this statement we analyzed the status of the native fish fauna of California, using a methodology that quantifies expert knowledge. Of 113 native taxa, 6 percent are extinct, 12 percent are officially listed as threatened or endangered 6 percent deserve immediate listing I7 percent may need listing soon, 22 percent show declining populations but are not yet in serious trouble, and 36 percent appear to be secure. Much of the faunal decline has taken place in recent years; it has included unexpectedly rapid declines of once abundant species. Fish taxa in serious trouble are most likely to be (1) endemic to California, (2) restricted to a small area, (3) occupants of just one drainage basin, (4) part of a fish assemblage of less than five species, and (5) found in isolated springs, warm water streams, or big rivers. Water diversions and introduced species, acting in concert, seem to be the principal causes of the decline of the native fauna, although other types of habitat degradation have contributed as well. The situation in California, with its high degree of endemism (60 percent), may be regarded as extreme but fish faunas in other temperate regions show signs of being nearly as stressed. It is likely that the situation with fish reflects a more general decline of the biota of temperate regions of the world.