Rivers need water — a fact that may seem ridiculously obvious, but in times of increasing water development, drought and climate change, the quantity of natural streamflow that remains in river channels is coming into question, especially in the Colorado River basin. Newly published research from Utah State University poses a tough question in these days of falling reservoir levels and high-stakes urban development: whether the continued development of rivers for water supply can be balanced with fish conservation.
Historically, the Colorado River basin has been highly dynamic with a wide range of streamflow, river temperatures and large sediment loads. Native fish evolved through periods of wet and dry cycles. But water-supply development has depleted the flow of many rivers in the Upper and Lower Colorado River basins, and today’s river habitats are increasingly decoupled from the natural cycle of spring snowmelt, monsoon-season floods and intervening low flows in favor of development and for stocking nonnative sports fish.
The health and recovery of native fish species now depends largely on the public’s willingness to protect rivers that retain some semblance of a natural flow regime as freshwater conservation areas, say authors Casey Pennock, Phaedra Budy, Wally Macfarlane and Jack Schmidt of the Watershed Sciences Department in the S. J. and Jessie E. Quinney College of Natural Resources and colleagues.
“Most people who study or manage fishes know that complex habitat required by native fish is created and maintained by adequate river flows, or a natural flow regime,” said Budy. “Nonetheless, society continues to manage our desert rivers as if we think that fish don’t need water. If we continue down this path, we will watch native fishes, some of which are found nowhere else on Earth, blink off the planet.”
Dams have changed the natural flow in many rivers in the Colorado River basin, but a more pressing problem is the depletion of flow such that little water remains in the channel. At a regional scale, water in the Colorado River basin is completely consumed and no water reaches the Gulf of California in most years. Even in the Upper Colorado River basin, some streams, such as the Duchesne, Price and San Rafael Rivers are nearly completely depleted of natural flow. If there is not enough flow in the river, other conservation efforts for native fish don’t really matter, say the authors.
Endangered fish recovery programs are designed not to interfere with existing or proposed future water development. The task of recovering endangered native fish populations may be an impossible goal wherever natural streamflow is declining due to a warming climate and wherever consumptive water uses are increasing, according to the authors. Despite decadeslong efforts by state, federal, tribal and private organizations, some native fish can’t maintain self-sustaining populations in the Colorado River basin today, and some species would be extinct without federal stocking programs.
“Managing for the minimum amount of water necessary to sustain native fish during dry spells is a common approach, but there are not many places where this strategy is sufficient to recover and protect native fish. We think conservation of natural flows is critical for long-term conservation of fish,” Pennock said. “In some rivers there have been attempts to recreate the benefits of natural flow with managed releases from large dams to reduce the negative downstream impacts of water development. These kinds of actions can have some localized benefit, but they are not likely to help native fish long-term or large-scale.”
Schmidt, who also directs Utah State’s Center for Colorado River Studies, stressed the importance of action.
“This study reminds us that increasing consumptive water use in an era of declining natural streamflow inevitably jeopardizes one of the Colorado River’s most distinctive attributes — its endemic native fishery,” Schmidt said. “If we care about protecting natural river ecosystems, then we as a society are going to have to care about leaving significant amounts of water in our rivers.”
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