Desert Tortoises (Gopherus agassizii) Fact Sheet: Population & Conservation Status

• 2004-2013: Population declines of 50% (US Fish and Wildlife Service 2021)
• 1987- 2006: decline of 3.5% per year for a 51% reduction in adults and subadults since 1987
  • Monitored populations of Sonoran Desert tortoises
• 1980s: major declines (33-77% over 10 years)
  • Documented at several western and one eastern Mojave Desert site in California.
• Population densities monitored by the Desert Tortoise Recovery Program
  • See their latest monitoring reports

Conservation Status

• IUCN Status
  • Critically Endangered- Gopherus agassizii (2020 assessment) (Berry et al. 2021)
  • Vulnerable- Gopherus evgoodei (2018 assessment) (Edwards et al. 2018)
  • TFTSG Provisional Red List: Critically Endangered (assessed 2011 2018) (Berry and Murphy, 2019; Rhodin et al., 2018).
• CITES Status
  • Appendix II (UNEP 2019)
• U.S. Fish and Wildlife Service (USFWS)
  • Mojave population: Threatened

History of Conservation

• 1972: State Reptile of California
• 1961: Illegal under California State law to collect desert tortoises.
• 1973. Desert tortoise listed as Threatened by federal government
• 1980: Beaver Dam Slope, Utah population of desert tortoises first to have federal protection
• 1980: Desert Tortoise Research Natural Area (DTNA) set aside as 102 sq km (39.4 sq mi) of natural habitat in Kern Co., California.
• 1989: Emergency listing as Endangered for Mojave population; collecting is a federal offense.
• 1989: Listed in California as Threatened
• 1989: State Reptile of Nevada
• 1990: Mojave population listed as threatened by USFWS
• 1991: USFWS rules population south and east of Colorado River (Sonoran) "not warranted".
• 2008: Petition filed to list Sonoran Desert tortoise under U.S. Endangered Species Act.
• 2009: Sonoran Desert population of tortoises may warrant listing by USFWS as a distinct population with a critical habitat (Federal Register Aug 28, 2009)
• 2009: 250-acre Desert Tortoise Conservation Center (DTCC) inLas Vegas, Nevada (established 1990); operated from 2009-2014 by San Diego Zoo in partnership with US Fish and Wildlife Service, Bureau of Land Management, Nevada Department of Wildlife, and Association of Zoos and Aquariums Conservation Centers for Species Survival. (San Diego Zoo Website 2010)
  • Establishing science-based methods to select sites for release in wild and conduct follow-up monitoring
  • Training professionals, teachers, community leaders on tortoise recovery issues
  • Conducting research on-site, including health research
  • Cultivating community support for tortoises in the wild
  • San Diego Zoo maintains pet tortoise pick-up service for stray or unwanted pet tortoises and tortoises found in urban areas of Clark Co., Nevada
• 2010: Around 1,000 desert tortoises brought to DTCC yearly
  • Many suffer effects of improper diet and care
  • After assessment, healthy tortoises are released into a 104 km sq (40 mi sq) protected habitat and monitored
  • Tortoises with metabolic bone diseases from lack of sunlight, and many other disease conditions are rehabilitated
• 2014: Desert Tortoise Conservation Center, near Las Vegas, closes
• 2017: Reserach funding obtained by the San Diego Zoo Institute for Conservation to again study survival and habitat use of desert tortoises
• 2018: San Diego Zoo Wildlife Alliance begins head-starting program (in partnership with USGS, Edwards Air Force Base, and BLM) (SDZG Press Release, 2018 Jun 29)

(Berry 1991) (Boarman 2001)

• Off road vehicle traffic
• Human collection and removal
• Cattle and wild burro grazing
• Roads, highways, railroads
• Military activity
• Vandalism
• Habitat destruction
• Toxic waste disposal
• Mining
• Global climate change and long term drought (USFWS 2009)
• Invasive non-native plants (Boarman 2001)
• Natural gas pipeline construction and maintenance (Olson et al 1996)
• Wild predators
  • Coyote and Kit fox (Kelly et al. 2021)
• Disease

• Renewed efforts needed to organize a coordinated, structured recovery program
  • Requires participation by collective groups of land and wildlife management agencies (National Fish and Wildlife Foundation 2022)
• Protection of critical habitat (USFWS 2021)
  • Adequate vegetation for shelter from high temperatures and predators
  • Nutrient rich forage species
  • Suitable geology for burrowing, nesting and overrwintering
  • Area for undisturbed movement, dispersal, gene flow
  • Mitigate human interference
• Six Recovery Units defined
  • Western Mojave Northern
  • Colorado Desert Eastern
  • Colorado Desert
  • Northeastern Mojave
  • Eastern Mojave
  • Upper Virgin River
• Designated a conservation-reliant species (Lovich et al. 2020)
  • Requires ongoing management by wildlife conservation professionals

Human disturbance, collection, and habitat loss pose the greatest threats to desert tortoises.

Image credit: © San Diego Zoo Wildlife Alliance. All rights reserved.

Berry (1991)
Boarman (2001)
California Fish and Game Website (2010)
Corn (1994)
Federal Register (Aug 28, 2009)
Rosmarino & Connor (2008)
Tortoise and Freshwater Turtle Specialist Group (1996)
USFWS (1991, 1994)
Van Devender (2002)
Zylstra & Steidl (2009)