A year after it returned to the Santa Cruz River following a decade-long absence, the endangered Gila topminnow now appears to be thriving there, advocates say.
The native Arizona species, listed under the Endangered Species Act in 1967, was found last year in the Santa Cruz River near Nogales for the first time since 2005. Annual surveys conducted in November confirmed that Gila topminnow remain in the river and have likely increased in number, a coalition of government, research and non-governmental agencies said in a news release this week.
“We are ecstatic to know the Gila topminnow appear to be thriving again,” said Tubac resident Sherry Sass of the Friends of the Santa Cruz River, an all-volunteer organization. “We have been tracking water quality and river conditions since the early-1990s. The return of this sensitive species speaks volumes about the river’s recovery.”
Survey methods do not estimate population numbers, but the ease with which the Gila topminnow were found this year suggests they are doing “very well,” advocates say.
Doug Duncan, fish biologist with the U.S. Fish and Wildlife Service, said he saw more than 200 topminnow in one pool.
“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,” he said.
Surface flows along most of the Santa Cruz River originate from effluent (treated wastewater) from the Nogales International Wastewater Treatment Plant in Rio Rico. In the past, the water was so polluted that no fish of any kind were found for several years. However, upgrades to the plant beginning in 2009 resulted in the elimination of odor and reduced levels of toxicity for fish, the groups said.
In addition, the improved effluent helped break down a clogging layer of algae and microorganisms that kept water from infiltrating into the groundwater table, and led to 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,” the news release said. “Scientists believe that cleaner water led to the fish’s return.”
This year’s survey was conducted by the Tucson-based nonprofit Sonoran Institute, U. S. Fish and Wildlife Service, University of Arizona, Tumacácori National Historical Park, Sonoran Desert Monitoring Network and other partners. The groups have been conducting the annual survey since 2008 as a means to track the overall health of the Santa Cruz River.
Others that actively participate in the effort include the Arizona Game and Fish Department, Friends of the Santa Cruz River, U.S. Geological Survey and Global Community Communications Schools at Avalon Gardens in Tumacacori.
The partners say the implications of the endangered topminnow discovery extend beyond Santa Cruz County and Arizona, since many southwestern rivers and streams depend on effluent for continued flows. As water becomes scarcer in the desert southwest, they say, the value of returning wastewater to the ecosystem will only increase.
“Often communities discharge effluent into rivers out of convenience and not with intent to benefit the environment,” said Claire Zugmeyer, ecologist at the Sonoran Institute and long-time coordinator of the annual fish survey. “We are now seeing that highly treated wastewater is a vital component to maintaining this region’s living river. With the release of effluent into the Santa Cruz and other rivers, we can create rich oases for both people and wildlife while simultaneously benefiting from functions provided by a healthy river, such as flood control, recharge, and cooling riparian vegetation.”