A Tale of Four Fish

Busy day with school, so here's a handful of aquarium shots from last December:

Colorado Pikeminnow (Ptychocheilus Lucius),
 Downtown Aquarium, Denver Co, CO 12/30/2013

Humpback Chub (Gila cypha),
Downtown Aquarium, Denver Co, CO 12/30/2013

Razorback Sucker (Xyrauchen texanus),
Downtown Aquarium, Denver Co, CO 12/30/2013

All of these species are native to the Colorado River drainage, and along with the Bonytail Chub (Gila elegans) they are the stars of a tragedy of environmental changes along the Colorado.

The first element in this tale is the dams -- most notably Hoover and Glen Canyon, but also including Imperial, Parker, Davis, and 9 more. These dams are responsible for drinking water, hydroelectric power, and irrigation for people in 5 states -- rather an important consideration. But, dams slow down or stop fish movements, and some of these fish migrate considerable distances to natal streams to spawn. (1) Dams alter river habitat, reducing flow rates both upstream and down, altering seasonal flood regimes, and typically lowering the temperature of water downstream. All of these impacts can reduce or even eliminate spawning by these fish. (2)

The next element in this tale is the introduction of non-native species, from parasites and diseases (3) to small cyprinids that compete with and often eat young native fish (4) and on to game fish such as Channel Catfish and Striped Bass (5) that we actively manage for. In the 1960's, the Federal Government actually poisoned the Green and San Juan Rivers (tributaries of the Colorado) in an attempt to remove native species to make room for preferred game fish! (6)

The final element here is the increases in population over the last few decades. Between 1990 and 2000, Arizona's population increased 40% and Nevada's increased 66%. By 2010, census records showed 2.7 million people living in the Colorado River Basin. That doesn't include the 18 million people living in and around Los Angeles, or the 1.3 million in San Diego, many of whom get their water pumped over the coast ranges from the Colorado River, or the water pumped into the Imperial Valley for irrigation. Historically, the river discharged an average of 16 million acre-feet into the Gulf of California. Today, the river frequently fails to reach the Gulf at all, a result of all that water we're pulling out of it. As people continue to move into these areas, demand for that water will only increase, and it simply isn't there! Which is going to make it increasingly difficult to manage water flows for the fish -- currently, populations of the Pikeminnow appear to be stable, the other three are decreasing. There are plans for river management and for reintroductions to suitable unoccupied habitat, but the increasing human pressure makes them increasingly difficult to carry out.

We spent millions of dollars on developing the river ($50 million in 1931 dollars, just to build Hoover Dam), and reaped untold millions in economic benefits as a result. But we're now spending millions of dollars on trying to recover these four endangered species, without any guarantee of success. With few exceptions, no one sets out to drive a species to extinction. It's usually a story of little tiny steps, each of which makes perfect sense, and no one of which can be labeled as the one that caused the species to decline. And yet, the IUCN lists nearly 20,000 species as at least threatened, out of only 70,000 that they've managed to evaluate.

Development isn't going to suddenly stop, and human population growth won't suddenly reverse itself, which means that we should continue to expect stories such as that of the Colorado Pikeminnow, Razorback Sucker, Humpback and Bonytail Chubs.

(1) Irving, D. B., & Modde, T. (2000). Home-range fidelity and use of historic habitat by adult Colorado pikeminnow (Ptychocheilus lucius) in the White River, Colorado and Utah. Western North American Naturalist, 60(1), 16-25.

(2) Tobin, Mitch. Endangered: Biodiversity on the Brink. Golden, CO: Fulcrum, 2010.

(3) Angradi, T.R., R.W. Clarkson, D.A. Kinsolving, D.M. Kubly, S.A. Morgensen. 1992. Glen Canyon Dam and the Colorado River: responses of the aquatic biota to dam operations. Prepared for the Bureau of Reclamation, Upper Colorado Region, Glen Canyon Environmental Studies, Flagstaff, Arizona. Cooperative Agreement No. 9-FC-40-07940. Arizona Game and Fish Department, Phoenix. pp. 155.

(4) Bestgen, K. R., Beyers, D. W., Rice, J. A., & Haines, G. B. (2006). Factors affecting recruitment of young Colorado pikeminnow: synthesis of predation experiments, field studies, and individual-based modeling. Transactions of the American Fisheries Society, 135(6), 1722-1742.

 

(5) Tyus, H. M., & Saunders III, J. F. (2000). Nonnative fish control and endangered fish recovery: lessons from the Colorado River. Fisheries, 25(9), 17-24.

 

(6) Holden, P.B. 1991. Ghosts of the Green River: impacts of Green River poisoning on management of native fishes. Pages 43-54 in W.L. Minckley and J.E. Deacon, editors. Battle Against Extinction: Native Fish Management in the American West. University of Arizona Press, Tucson. pp. 517.