Successful mechanical removal of green sunfish from closed systems in southern Arizona

Aravaipa and Bonita Creeks are unique aquatic systems in southern Arizona as they still support intact or nearly intact native fish communities. Bonita Creek is located within the Gila Box Riparian National Conservation Area and is characterized by deep pools, undercut banks, and woody debris from beavers. Aravaipa Creek flows for 17 miles, including 10 miles through the Aravaipa Canyon Wilderness, where cliffs tower over 1,000 feet high and aquatic habitat is comprised of pools, riffles, glides, and runs.       

Bonita Creek is home to many native fishes, including federally endangered Gila chub (Gila intermedia) and Gila topminnow (Poeciliopsis occidentalis), longfin dace (Agosia chrysogaster), speckled dace (Rhinichthys osculus), desert sucker (Pantosteus clarkii), and Sonora sucker (Catostomus insignis). Aravaipa Creek is equally diverse, with federally endangered loach minnow (Tiaroga cobitis) and spikedace (Meda fulgida), speckled and longfin dace, desert and Sonora sucker, and roundtail chub (Gila robusta). 

Introduced non-native fish species invaded and established self-sustaining populations in both creeks. Non-native fish species pose a significant threat to the survival of the native fish. Non-natives include western mosquitofish (Gambusia affinis), fathead minnow (Pimephales promelas), yellow bullhead (Ameiurus natalis), and green sunfish (Lepomis cyanellus) for Bonita Creek and the latter two non-natives and red shiner (Cyprinella lutrensis) in Aravaipa Creek. The green sunfish, which is native to eastern North America, is of particular interest and concern as this species feeds aggressively on other fishes and was deemed by fish biologists as the most significant threat to native fishes in both creeks. Green sunfish were first detected in Aravaipa Creek in 1963 and have resided there for over 50 years. It is unknown when green sunfish first appeared in Bonita Creek. The native fishes in both Aravaipa and Bonita creeks have thus faced direct competition for food and habitat and have been preyed upon by green sunfish and other non-native fish species for years.  

The Bureau of Reclamation, to prevent further threats of non-native species invasions, constructed fish barriers across both creeks as part of the Gila River Basin Native Fishes Conservation Program. The Aravaipa fish barrier was constructed in 2001 and is located approximately five miles above its confluence with the San Pedro River, whereas the Bonita Creek barrier was constructed approximately 1.3 miles upstream from its confluence with the Gila River in 2008. After the Bonita barrier was constructed, the creek was chemically treated to eradicate non-native fishes as part of a multi-agency native fish restoration project. The chemical treatment failed to eliminate the non-native fishes from the treatment reach. As such, additional mitigation strategies, including mechanical removal, were used to remove expanding non-native fish populations, with an emphasis on green sunfish, first in Bonita Creek and then in Aravaipa Creek. Removal of green sunfish in Aravaipa Creek focused primarily on Horse Camp Canyon, a tributary to Aravaipa Creek, as surveys revealed that it was the only point source for green sunfish into Aravaipa creek. Horse Camp Canyon flows intermittently; however, seasonally, during high flows it is connected to Aravaipa Creek, and sunfish may actively or passively move downstream into the mainstem. 

Removals started in 2009 at Bonita Creek and 2010 at Horse Camp Canyon. In 2013, additional BLM funding resulted in increased removal efforts and subsequent eradication of sunfish by 2015 in Horse Camp Canyon. From 2010-2015 close to 4,000 sunfish were removed from Horse Camp Canyon. In 2016, the Bonita Creek project received additional funding that was pivotal for increasing capacity for removal efforts. With increased funding, additional technicians and interns were hired and sampling effort was increased at Bonita Creek to four days per week all year. From 2009-2017, a total of 24,107 green sunfish was removed from Bonita Creek.  

In both Bonita and Aravaipa Creeks the study areas were isolated from upstream reinvasion by constructed fish barriers. Removal efforts were also scheduled to maximize the removal of adults immediately prior to peak spawning activity.  Timing of removal effort was as important as the amount of effort expended. Additionally, multiple removal efforts were required in the same year. This may be a requirement for any removal study regardless of study system size.  

It took nine years to eliminate green sunfish from Bonita Creek and six years from Horse Camp Canyon. We assume complete eradication of green sunfish in the lower Bonita Creek based on six years of continued monitoring data with zero green sunfish captures, and zero detection of green sunfish DNA in 2021 at four sites within the project area.   

The success of these efforts demonstrates how perseverance and great partnerships can result in major benefits to threatened and endangered species and their habitats.