From U.S. Fish & Wildlife Service Southwest Region:

Endangered Fish Thriving in Santa Cruz River!

The endangered Gila topminnow, which returned to the Santa Cruz River after a 10 year absence, now appears to be thriving. The native Arizona species, was found last year in the Santa Cruz River near Nogales, Arizona for the first time since 2005. Annual surveys conducted in November confirm that Gila topminnow remain in the river and have likely increased in number.

“At one site I saw a small pool with over two hundred topminnow. We are thrilled to be finding them this numerous since this is a good indicator that their return last year was not a brief blip on the radar,” says Doug Duncan, fish biologist with the U.S. Fish and Wildlife Service.

Surface flows along most of the Santa Cruz River originate from effluent (highly treated wastewater), and have in recent decades been so polluted that no fish of any kind were found for several years. Massive upgrades to the Nogales International Wastewater Treatment Plant beginning in 2009 resulted in the elimination of odor, reduced levels of toxicity for fish, and a breakdown of a clogging layer of algae and microorganisms that kept water from infiltrating into the groundwater table. University of Arizona scientists found that this clogging layer was largely responsible for an eight mile die-off of trees along the Santa Cruz River near Rio Rico in 2005.

After the treatment plant upgrades were completed, scientists and local residents eagerly awaited the fish's return as the water quality in the river began improving. Scientists believe that cleaner water led to the fish’s return. Survey methods do not estimate population numbers, but the ease with which the Gila topminnow were found this year suggests that they are doing very well.

Learn more: http://tinyurl.com/sc-tminnow

Photo of Gila topminnow courtesy of George Andrejko, Ariz Game & Fish Dept.

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