Rivers need water – a fact that may seem ridiculously obvious, but in times of increasing water development, drought and climate change, the amount of natural flow that remains in river channels is called into question. , especially in the Colorado River Basin. Recently published research poses a difficult question in these times of declining reservoir levels and high-stakes urban development: whether the continued development of rivers for water supply can be balanced with fish conservation.
The Colorado River Basin is historically a very dynamic river with a wide range of river flows throughout the year, a wide range of river temperatures, and significant sediment loads in certain seasons. Native fish evolved through periods of wet and dry cycles when the total flow was relatively high or relatively low. But water supply development has further depleted the flow of many rivers in the upper and lower Colorado River basins, and today’s river habitats are increasingly decoupled from this natural cycle of snowmelt. spring and monsoon season floods and low intermediate flows favor the depletion of natural resources. sink and stock non-native sport fish in some locations. The health and recovery of native fish species now largely depends on the public’s willingness to protect rivers that retain some semblance of a natural flow regime as fwetland conservation areassay authors Casey Pennock, Phaedra Budy, Wally Macfarlane and Jack Schmidt of the SJ Department of Watershed Sciences and Jessie E. Quinney College of Natural Resources and their colleagues Matthew Breen of the Utah Division of Wildlife Resources and Justin Jimenez from the US Bureau of Land Management.
“The bottom line is that everyone knows fish need water, and most people who study or manage fish know that the complex habitat required by native fish is created and maintained by adequate river flows. or a natural flow regime,” Budy said. “The White River of Colorado and Utah is a perfect example of such a natural river; it is the only tributary of the four considered in our research that still has a natural flow regime and it is the only tributary medium green river with an abundance of complex fish habitat and a thriving native fish community. Nevertheless, society continues to run our desert rivers as if we think fish don’t need water. If we continue in this way, we will observe the native fish, some of which are found nowhere else on Earth, stay away from the planet.”
Natural flows are vital to the health of rivers. The survival of native fish populations, water quality, and river habitats all depend on the varying flood and baseflow flows that rivers experience when left to their own devices. The dams have altered the natural flow of many rivers in the Colorado River Basin, but a more pressing problem is depleting the flow so that little remains in the channel. Regionally, the water in the Colorado River Basin is entirely consumed, and no water reaches the Gulf of California in most years. Thus, the river delta in Mexico has changed from an internationally recognized haven of biodiversity to a dry, sandy channel. Even in the upper Colorado River basin, some streams, such as the Duchesne, Price, and San Rafael rivers, are almost completely depleted. The decline of native fish has been deep and persistent. If there’s not enough flow in the river, other conservation efforts don’t really matter, the authors say.
Endangered fish recovery programs designed to help native fish populations are required by law to use strategies that benefit endangered fish, but these programs cannot interfere with the development of the water existing or proposed in the future. Thus, these recovery programs are limited in protecting the one thing fish need most: water. According to the authors, the task of restoring endangered native fish populations may be an impossible goal wherever the natural flow of rivers decreases due to global warming and water consumption increases. Despite decades-long efforts by state, federal, tribal, and private organizations, some native fish cannot maintain self-sustaining populations in the Colorado River Basin today, and some species would be extinct without federal restocking programs. The long-term conservation of native fish is directly linked to natural flow, the authors say, and very few rivers still retain this function.
“Managing the minimum amount of water needed to sustain native fish during droughts is a common approach, but there aren’t many places where this strategy is sufficient to recover and protect native fish. We believe conservation of natural flows is essential for long-term conservation of fish,” Pennock said. “In some rivers there have been attempts to recreate the benefits of natural flow with managed discharges of large dams to reduce negative downstream impacts of water development. These types of actions may have localized benefits, but they are not likely to help native fish. long-term or large-scale, as societal needs, drought, climate change and infrastructure limit the amount of water available to rivers. »
“This study reminds us that increasing water use at a time of declining natural flow caused by climate change inevitably jeopardizes one of the Colorado River’s most distinctive attributes – its endemic native fishery,” said Schmidt, who also directs Utah State’s Center for Colorado. River studies. “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.”
According to the authors, what native fish need is access to adequate water in rivers to sustain the complex, nuanced and disorderly flows in which they have evolved.