Swimming with Mastodons

Image: Danielle Tremblay of Colorado Parks and Wildlife holding a Colorado pikeminnow captured in the Colorado River near Grand Junction.

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The Colorado pikeminnow – Ptychocheilus lucius – is a behemoth river fish capable of growing to six feet and more than eighty pounds. For at least three million years, lucius has been the Colorado River’s top aquatic predator, devouring smaller fish and even mice and rabbits when big spring floods sweep them into the river.

Pikeminnows have co-existed with mastodons and mammoths, ice ages and lava flows, and the river’s carving of the Grand Canyon.

They live only in the Colorado River basin.

The fish were once so plentiful that farmers in the Salt and Gila River valleys of Arizona frequently pitchforked them out of irrigation canals to keep them from stacking up like piscine logjams and spilling water headed for farms. But today, this fish species is one of our country’s most endangered, teetering on the brink of extinction. As reported in a 2018 population viability analysis, “If current management conditions are allowed to persist into the future…….the Green and Upper Colorado River sub-basin populations will continue to decline at an annual rate of 6 – 7%.”

The pikeminnow faces the very real prospect of soon becoming a fish out of water. Last year, following meager snowmelt runoff and heavy water diversions to farms and cities throughout the summer, the fish’s last remaining river habitats had nearly dried up by September. The Yampa River barely trickled through Dinosaur National Monument in western Colorado, where pikeminnow have for millennia gathered to spawn in the shadow of “Cleopatra’s Couch,” a rock outcrop so named for reasons having nothing to do with the reproductive activity of lucius.

In another critically important river habitat in the Colorado River near Grand Junction (the “15-Mile Reach”), river flows dropped to less than one-tenth of the absolute minimum that fish biologists have said are necessary to sustain pikeminnow and other highly-endangered fish (see graph below).

Image: The US Fish & Wildlife Service has set minimum flow targets for sustaining pikeminnow in the 15-Mile Reach of the Colorado River near Grand Junction, Colorado. During last September (2018), river flows were less than one-tenth the prescribed level.  Flow data: US Geological Survey

The population viability analysis found that when August-September flows are maintained within the targeted range, pikeminnow in the Green River sub-basin produce nearly three times more offspring than when flows don’t meet the targets; in the Upper Colorado River, reproduction is five times higher when targets are met. These findings are of particular concern in the Green River sub-basin — which includes the Yampa River — due to the fact that target flows were achieved only 10% of the time in recent decades.

The extremely low flows in the Colorado River basin last year resulted from too much water being extracted from rivers that are already diminished from global warming. According to climate scientists Brad Udall and Jonathan Overpeck, the Colorado has been flowing at 20% less than average for the past two decades, and much of that reduction is attributable to warmer temperatures. They forecast further loss of 20-30% of the river’s flow by 2050 as the climate warms further.

Add the pressure of trying to serve a rapidly growing population with reliable water supplies and you have a wickedly challenging water equation to solve.

How, then, can we leave more water in the river to support pikeminnow and aquatic ecosystems and thriving recreational and tourism economies dependent upon healthy, flowing rivers?

The best way to solve this water equation is to extract less water from rivers in the basin (aka ‘demand management’). While it is very hard to imagine how you could motivate 40 million people to use less water to save a giant minnow, it looks like a bizarre twist of fate may now align the financial, political, and legal forces necessary to reduce water consumption in the basin.

As it turns out, both the pikeminnow and “Front Range” cities in Colorado are facing very serious water risks in coming years. If Colorado and its neighboring ‘upper basin’ states of Utah, Wyoming, and New Mexico are unable to send enough water downstream to the ‘lower basin’ states of Arizona, Nevada and California to meet their obligations under the venerable water-sharing agreement known as the Colorado River Compact, the lower basin states will surely protest; at that point, the ‘junior’ water rights of Denver and other Front Range cities would be vulnerable to curtailment, with very disruptive economic consequences.

Under the 1922 Colorado River Compact (the “Law of the River”), the upper basin states of Colorado, Wyoming, New Mexico, and Utah must release an average of 75 million acre-feet of water every 10 years from Lake Powell for use by the lower basin states of California, Arizona, and Nevada. Map courtesy of US Geological Survey

This nightmarish scenario is motivating a great deal of discussion about demand management, and how it could be implemented at the necessary scale. The concept is simple: if less water can be extracted from the river, more water will flow downstream through pikeminnow habitats and into Lake Powell, where it can be released to the lower basin.

To be equitable and cost-effective, both cities and farmers will need to share in implementing demand management. As I discussed in a recent post, many cities including Denver have made remarkable progress in reducing their total water needs even while their populations have grown substantially. Political leaders representing Front Range cities can – following the example set by Los Angeles Mayor Eric Garcetti – continue incentivizing residents to further lessen their water demands so that their cities can reduce the substantial volume of water being extracted from the headwaters of the Colorado River.

Urban participation in demand management will be a very important show of good faith to farmers that will be expected to contribute the lion’s share of demand management.

By working collaboratively with Western Colorado farmers – particularly in the Yampa watershed and Grand Valley upstream of critical fish habitats – Colorado’s water managers can pay farmers willing to voluntarily and temporarily cut back on some of their water use during dry years, allowing the conserved water to flow through pikeminnow habitats and downstream into Lake Powell and the lower basin.

Such demand management in cities and on farms will preserve both the right of Front Range cities to continue pulling water through their trans-mountain diversions and give fish the water they desperately need.

Two-thirds of the Colorado River basin’s native fish are already gravely imperiled by river flow depletions. It is incomprehensible to think that a fish like the pikeminnow that has persisted for millions of years could perish on our watch, simply because we’re using more water than we absolutely need. We can live compatibly with these remarkable creatures but we need to act swiftly and decisively — before time, and water, run out.

Image: A nearly dried up Colorado River within 15-Mile Reach near Grand Junction, Colorado in September 2018. Photo by Brian Richter