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The Crystal Darter (Crystallaria asprella) requires large, clear-water streams with clean sand and gravel bottoms and moderate to swift currents. It is intolerant of siltation and other forms of pollution from various land use practices. Direct habitat degradation from damming, channelization, and dredging has also reduced habitat for this species. Remaining populations have become isolated from one another by dams and impoundments. The Mississippi River most likely no longer serves as a usable corridor for the Crystal Darter because of the silt load. The isolated local populations are then vulnerable to single destructive events such as toxic chemical spills.
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The Bering Cisco (Coregonus laurettae) is endemic to Alaska and is present primarily along the State’s west and north coasts. It is known to spawn in only three river systems – the Yukon, Kuskokwim, and Susitna Rivers. Genetic research indicates that each of these populations is distinct. The Bering Cisco has been observed to migrate more than 1,200 miles into freshwater streams to spawn. Unlike salmon, some of these fish survive spawning runs. Since this species is slow-growing but short-lived, it is highly vulnerable to alterations in stream flow or water quality and large-scale environmental disasters.
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Available data for the American Eel (Anguilla rostrata) indicate that, overall, there have been declines in recruitment, population, and escapement during three generations (36 years). A recent report indicated that barriers to migration (dams and weirs), passage through turbines at hydropower dams, habitat degradation or loss, and overharvest were likely the greatest threats by humans across the species’ range. Although eels are able to ascend many smaller barriers, recent studies have documented a tenfold reduction in eel density above each potentially passable barrier. For example, the number of juvenile eels migrating to Lake Ontario passing over hydropower dams fell from 935,000 in 1985 to approximately 8,000...
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The Waccamaw Silverside (Menidia extensa) has a very limited distribution confined to Lake Waccamaw in North Carolina, a lake with neutral pH levels from underlying limestone formations in an area of acidic natural waters. This species is found in large schools and often over dark-colored substrates. Its limited habitat is threatened by nutrient loading caused by the runoff of organic matter and agricultural chemicals.
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The Ironcolor Shiner (Notropis chalybaeus) is found in deep pool areas of creeks and small rivers and is often associated with aquatic vegetation. This species needs clear sandy areas for spawning. Populations of Ironcolor Shiner are in decline due to increased turbidity, siltation, and pollution.
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