Changes in Fish Assemblages in the United States: Extent, Causes, and Conservation

摘要

Native fish assemblages in large rivers in the United States have changed dramatically in the past century. We use regional examples of 10 rivers in continental North America to commence to evaluate these changes in fish assemblages. Four of the 10 rivers are the 1st, 4th, 10th, and 16th longest in the United States. To a large extent, translocations and introductions of nonnative and alien species, flow alteration, and habitat loss have been the primary causative factors of decline of native fish assemblages. Mainstream dams, irrigation diversions, channel alteration and simplification, groundwater mining, agriculture, and pollution have been the primary drivers of the negative impact on historical aquatic habitats. Introduction and translocation of fishes into river systems within the United States over the past century have been largely directed at increasing sport fishing opportunity. However, accidental introductions and those for bait, the aquarium trade, and biological control in combinationalso have impacted native assemblages through habitat competition, hybridization, and direct predation. As a result, many of the native species are either listed or becoming increasingly rare. A critical question relative to the theme of this Fourth World Fisheries Congress is, "Can we reconcile the current situation and conserve and sustain native fish assemblages in many of these rivers in the United States?" Conservation activities including hatchery and refuge propagation, management by river basinor watersheds, barrier construction, and safe harbor agreements are being used to sustain native fish assemblages. Notwithstanding, the current plight of native fishes in many river basins in North America can be described as a "battle against extinction."