Loss of Biodiversity in Aquatic Ecosystems: Evidence from Fish Faunas

Fishes are appropriate indicators of trends in aquatic biodiversity because their enormous variety reflects a wide range of environmental conditions. Fish also have a major impact on the distribution and abundance of other organisms in waters they inhabit. Examination of trends in freshwater fish faunas from different parts of the world indicate that most faunas are in serious decline and in need of immediate protection. Species most likely to be threatened with immediate extinction are either specialized for life in large rivers or are endemic species with very small distributions. We conservatively estimate that 20 percent of the freshwater fish species of the world (ca. 1800 species) are already extinct or in serious decline. Evidence for serious declines in marine fishes is limited largely to estuarine fishes, reflecting their dependence on freshwater inflows, or to fishes in inland seas. The proximate causes of fish species’ decline can be divided into five broad categories: (1) competition for water, (2) habitat alteration, (3) pollution, (4) introduction of exotic species, and (5) commercial exploitation. Although one or two principal causes of decline can be identified for each species, the decline is typically the result of multiple, cumulative, long-term effects. Ways to protect aquatic biodiversity include the implementation of landscape-level management strategies, the creation of aquatic preserves, and the restoration of degraded aquatic habitats. Without rapid adoption of such measures we are likely to experience an accelerated rate of extinctions in aquatic environments as human populations continue to expand.