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Rare Fish Return Home
by Craig Springer, US Fish and Wildlife Service
Craig_Springer at fws_gov
Until recently, Bylas Springs, a complex of three small springbrooks on the San Carlos Apache Nation in Arizona, was overrun with non-native mosquitofish and choked with thirsty salt cedar trees. The native Gila topminnow, once perhaps the most common fish in southern Arizona, had been displaced by aggressive mosquitofish and had become one of the most endangered vertebrates in the United States.
Today, however, the topminnow is making a return to the Gila river system where it once thrived in sloughs, backwaters and tributary springs, thanks to a cooperative reintroduction program spearheaded by the Service's Arizona Fishery Resource Office.
In 1968, biologists discovered the Gila topminnow in Bylas Springs. By 1980, these tiny fish were in big trouble. The non-native mosquitofish invaded the springs via a flooded Gila River where the mosquitofish thrives.
This new inhabitant to Bylas Springs spelled doom for the native fish. The aggressive and predacious mosquitofish displaced the topminnow rapidly, prompting the Service to list the topminnow as an endangered species.
When biologists first discovered mosquitofish in Bylas Springs, the Service took immediate steps to protect the remaining Gila topminnow. They moved as many topminnow as possible to ponds at Roper Lake State Park and the Arizona State University Fisheries Laboratory, maintaining them for future reintroduction efforts.
Those efforts have paid off. A cooperative project undertaken by the Arizona Fishery Resource Office, the San Carlos Apache Tribe, and the Arizona Game and Fish Department turned the springs back into an environment hospitable to native animals such as the topminnow as well as native plants.
Biologists erected concrete barriers near the river to prevent mosquitofish from reentering the springs. Fences around the springs protect them from livestock trampling. Cottonwoods and willows have replaced the water-guzzling salt cedars and are casting their cooling shade upon the water.
Biologists also created along the springbrook several large open pools--the favorite habitat of the topminnow.
"In our restoration efforts, we've tried to recreate the topminnow's natural habitat," said Service biologist Cliff Schleusner, who organized the project.
"Historically we've found the topminnow in open pools of spring habitats. By protecting topminnow from the plants and animals that shouldn't be here and creating the pools, we're sure that we've indeed created their preferred habitat," Schleusner said.
The proof, as the saying goes, is in the pudding. Schleusner points out that the released topminnow show a strong partiality to the pools and are doing quite well. They have already reproduced.
Bylas Springs now harbors just two of the 11 known populations of Gila topminnow and this imperiled fish is one step closer to recovery.