Freshwater fishes of the Amazon River basin: their biodiversity, fisheries, and habitats

摘要

Stretching more than seven million square kilometers, the Amazon River basin is the largest river basin in the world and discharges about one-sixth of all freshwater from the continents to the oceans of the world. The age of this ecosystem, its position near the equator and the enormous diversity of its aquatic habitats, have produced the most diverse fish fauna on the planet. About 2,500 fish species have already been described and it is estimated that more than 1,000 new species remain to be discovered. Knowledge concerning this multitude offish species is still insufficient, which makes their management and protection difficult. About 50% of the species are thought to occur in the large rivers and connected floodplains and another 50% in headwater streams. Inland fisheries give rise to 450,000 t of fish each year and thus contribute substantially to the protein supply of local populations. However, despite their economic importance, these fisheries receive little attention from the respective governments. The fisheries are highly selective and several stocks of large species with high market value have been over fished. Fish culture is still in its infancy but its development is expected to provide high-quality species during periods of low supply. Over large areas, aquatic habitats are still in near-natural conditions because of the low densities of resident human populations. Nonetheless, over the last few decades, the pressure on aquatic ecosystems and habitats has steadily increased, mainly due to large-scale destruction of natural vegetation cover by agro-industries in the savanna belt (cerrado), small-scale agriculture in the Andean hill slopes, and logging in rain forests. These activities have placed aquatic biodiversity, including fishes, at serious risk. Many headwater species have restricted distributions and are therefore particularly vulnerable to large-scale environmental degradation. Moreover, the construction of large reservoirs for hydroelectric power generation has serious consequences for fish fauna. Currently, about 16.4% of the Amazon River basin is protected, and another 15.2% is under partial protection in indigenous reserves in Brazil. Another 9.1% will be implemented as reserves in the next 10 years in the Brazilian part of the basin. The formulation by the Amazonian countries of a coherent policy that integrates long-term management of the river basin with sustainable management of aquatic and wetland habitats, including their fauna and flora, is urgently needed.