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  • A year later and Mission Garden’s topminnow are thriving

    Oct 07, 2020 | Read More News
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    Dragonflies and damselflies dance over the water. Toads are hopping. In short, in the year since the endangered Gila topminnow were released into the waters at Pima County’s Mission Garden, the native fish species has thrived. 
    “The Garden and canal really are humming with growth and life,” said Ian Murray, a conservation biologist with the Pima County Office of Sustainability and Conservation.  
    Surveying topminnow
    In June 2019, the Arizona Game and Fish Department, in cooperation with the U.S. Fish and Wildlife Service, introduced 500 Gila topminnow into the newly created representation of an irrigation acequia, or canal, at Mission Garden, 946 W. Mission Lane.

    Mission Garden is a living agricultural museum of heritage fruit-trees, traditional local heirloom crops and edible native plants at the site of Mission San Agustin del Tucson. Pima County purchased the site with 1997 voter-approved bond funds in order to conserve important cultural sites.

    In the year since the fish were released into the acequia, the vegetation within and adjacent to the canal has blossomed with new growth, creating a lush oasis, including some prolific growth of the endangered Huachuca water umbel, which was planted last year.  

    Murray and other biologists with the Pima County Office of Sustainability and Conservation recently revisited Mission Garden to assess the health of the fish and other wildlife populations. Working with help from Mission Garden co-chair Katya Peterson and aquatic habitat designer Dennis Caldwell, biologists saw dragonflies and damselflies of several species, including gaudy orange flame skimmers, dancing over the water. Several Sonoran Desert toads bounced into dense vegetation along the banks and the shed skin of a checkered garter snake was found. 

    Along the length of the canal, topminnow appeared to be thriving and prolific, with large numbers of juvenile fish as well as mature individuals. The researchers observed numerous dark black males courting the longer and bulkier females near the water’s surface.  

    To monitor the fish population, biologists set a number of mesh minnow traps baited with dog food.  The traps were set for roughly two hours and the number of fish caught per trap tallied in a counting bucket before the fish were released. In this way researchers could calculate a catch per unit effort, effectively standardizing the number of fish captured.  

    In all, 16 traps were set across the entire length of the canal and 1,302 topminnow were captured.  On average, each trap caught 46 fish per hour.  

    While 1,300 topminnow seems like a lot, it was likely only a fraction of the fish population in the canal.  

    In addition to the other amenities at Mission Garden, the successful introduction of topminnow makes the location a great respite and oasis, whether assisting with the propagation of heirloom crops, enjoying the scenery, or pondering aquatic life.