© Mike Norton (Colorado)

Colorado River Endangered Fishes

The Razorback sucker, Humpback chub, and Pikeminnow were once widespread and common in the large rivers that feed into the Colorado River, including the Yampa, Green and Gunnison Rivers.  These were once very large fish, sometimes reaching six feet in length.  Today, the few remaining fish never reach this size.  All of these fishes are federally listed as threatened or endangered, and Colorado has only a few remaining sites where these fishes can be found.  The demise of these fishes began when early settlers caught them in huge numbers, reducing the abundance of individuals but not really threatening the populations.  This situation worsened when a combination of threats, including dams and introductions of exotic game fish changed the fundamental characteristics of natural aquatic ecosystems.  The large dams changed the temperature and flows in the rivers.  Prior to construction of the large dams, the flow cycles of these rivers were characterized by low flows (sometimes frozen) during winter, raging cold-temperature flows during peak snow melt (June), and warm placid flows during late summer/early fall.  The large dams have “tamed” the rivers and now very little fluctuation exists in the temperature and flows of these large rivers, thus rendering the habitat much less suitable for these native fish.  In addition to altered stream flows and temperature gradients, stresses on native fish are exacerbated by introduced species of game fish, which outcompete native fish for resources, and may predate upon them as well.  The Yampa River is the last remaining relatively free flowing large river in Colorado.  It is now threatened with numerous water development projects that threatened the remaining natural spawning habitat in the state.

Efforts to restore habitat and reintroduce our endangered fish are on-going by Colorado Division of Wildlife, the U.S. Fish and Wildlife Service, Colorado State University’s Larval Fish Lab, and The Nature Conservancy.

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