General causes of biodiversity decline
The close of the 20th century witnessed a number of wellpublicized environmental problems of regional and international scale. Each problem contributed to declines in fish biodiversity (Safina 2001a). In addition to habitat modification, species introductions, pollution, and commercial exploitation, global climate change is recognized as a growing threat to aquatic ecosystems and fishes (IPCC 2007d; Climate change and fishes). An additional problem is our collective inability to learn from past experiences. We thus repeat our mistakes, as has happened to salmon fisheries in continental Europe, then the British Isles, followed by the northeastern USA and Canada, and finally the eastern Pacfi c and Japan (Montgomery 2003). These interacting causes result in direct population losses due to mortality or reproductive failure, or indirect losses due to hybridization or loss of genetic diversity. At the root of each problem is human overpopulation and overconsumption. Overpopulation is particularly destructive to aquatic ecosystems and to fishes because humans are concentrated along rivers and estuaries.