According to a report published by PPIC, the best documented indicators of declining aquatic environments in California are fish (Moyle and Williams 1990; Moyle 2002; Howard and Revenga 2009).
Of 129 kinds of native fish in California, 5 percent are extinct, 24 percent are listed as threatened or endangered species, 13 percent are eligible for listing today, and another 40 percent are in decline (Figure B). In other words, over 80 percent of the native fishes are extinct or imperiled to a greater or lesser degree.
The number of imperiled species is increasing rapidly. Since the first state - wide assessment in 1985, fish species have been listed under state and federal Endangered Species Acts (ESAs) at a rate of about one species per year, with 31 listed by 2010. Most native fishes are endemic only to California (60 percent) or to the interstate waters of California, Nevada, and Oregon (19 percent). Thus, their decline is largely due to factors in California, mostly related to human water and land management.
Clearly, environmental management actions in recent decades have been far from sufficient to reverse these declines. An analysis by Richter et al. (1997b) indicates that the loss of freshwater biodiversity in the western United States primarily results from altered hydro - logic regimes, pollution (especially nonpoint source pollution), and invasions of alien species.
Read more on the PPIC website at this link:
In 2015, the Ca DFW, working with UC Davis, issued the 3rd revision of the California Fish Species of Special Concern. These are defined as those species, subspecies, Evolutionary Significant Unit, or Distinct Population Segment of native fish that currently satisfy one or more of the following (not necessarily mutually exclusive) criteria:
- are known to spawn in California's inland waters;
- are not already listed under either federal or state endangered species acts (or both);
- are experiencing, or formerly experienced, population declines or range retractions that, if continued, could qualify them for listing as threatened or endangered status;
- have naturally small populations exhibiting high susceptibility to risk from stressors that, if realized, could lead to declines that would qualify them for listing as threatened or endangered.
Species accounts were prepared for the 62 taxa determined to be of special concern to address the following: overall status, description, taxonomic relationships, life history, habitat requirements, distribution, trends in abundance, nature and degree of threats, effects of climate change, status determination (scoring) and management recommendations. Maps showing current and historic range accompany each account.