Tiny endangered pupfish return to this lake east of Phoenix after a year's absence

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05-04-2025

After more than a year of waiting, Ayer Lake in Superior is once again home to hundreds of tiny endangered desert pupfish.
The Arizona Game and Fish Department released 450 pupfish into the lake on March 26, according to a news release. The lake — part of the Boyce Thompson Arboretum — was drained in 2023 for urgent dam repairs.
'The release of the pupfish into Ayer Lake was an experience I will not forget,' said Superior Mayor Mila Besich, who helped net and release some of the fish herself.
Arboretum staff had kept the lake's fish population safe in a greenhouse during the repairs, according to Boyce Thompson's Executive Director Kim Gray.
'They have been very happy and have even produced offspring,' Gray said in the release.
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Those fish and their offspring joined others from refuge sites at Robbins Butte Wildlife Area and the Phoenix Zoo during the reintroduction. The reintroduction took place through an agreement among the arboretum, AZGFD, and the U.S. Fish and Wildlife Service, which outlines a collaborative effort for protecting the fish.
Gray called the pupfish's return 'a moment of hope' for the species, which has seen its numbers decline dramatically in the wild over the past century.
Desert pupfish are small — usually under three inches long — and hardy. They can survive extreme temperatures, high salinity and low oxygen levels. Despite that resilience, they are listed as endangered in the United States, having vanished from most of their historical range after losing habitat and facing pressures from non-native fish like tilapia and mosquitofish.
Today, remnant populations survive in a handful of places in Arizona, California's Salton Sea region, and parts of Sonora, Mexico. In Arizona, a network of carefully managed refuge sites like Ayer Lake helps keep the pupfish going.
Brett Montgomery, AZGFD's specialist for topminnow and pupfish species, said Ayer Lake is especially well suited for pupfish because of its stable conditions and isolation from invasive species. AZGFD also plans to reintroduce Gila topminnow, another endangered species, to Ayer Lake once the pupfish have time to adjust.
'It's such a nice habitat where the fish will really have the chance to thrive,' Montgomery said in the release.
Pupfish help manage the lake's ecology by feeding on mosquito larvae and aquatic invertebrates, which can help reduce pest populations and control algae growth.
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The arboretum works to maintain the lake as a suitable habitat for the endangered species.
'The arboretum has abundant wildlife and we actively curate our garden spaces to accommodate the various species that make their home here,' said Gray.
To keep that habitat intact, officials urged the public not to move fish in or out of Ayer Lake for any reason.
'Introducing a non-native species to this lake could mean we have to start this entire process over,' Montgomery said. 'It would wipe out years of work.'
Austin Corona covers environmental issues for The Arizona Republic and azcentral. Send tips or questions to [e-mail]
Environmental coverage on azcentral.com and in The Arizona Republic is supported by a grant from the Nina Mason Pulliam Charitable Trust.
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This article originally appeared on Arizona Republic: Endangered pupfish swim free again at Boyce Thompson