Medica, PA, KE Nussear, TC Esque, MB Saethre. 2012. Long-term growth of desert tortoises (Gopherus agassizii) in a southern Nevada population. Journal of Herpetology 46(2): 213:220. doi: 10.1670/11-327
Knowledge of growth rates, age at maturity, and longevity are important aspects of a species life history and are directly applicable to life tables and population viability analyses. We measured the growth of a cohort of 17 semi-wild Desert Tortoises (Gopherus agassizii) located in Rock Valley, Nevada over a 47-yr period beginning in 1963. The tortoises were initially marked as hatchling and juvenile animals between the years 1963 and 1965, and were assigned ages of 1–4 yr to the tortoises at initial capture based on their body size. These tortoises were recaptured, measured, and weighed approximately annually since their initial capture. Growth of male and female tortoises did not differ significantly until animals reached the age of 23–25 yr. Annual tortoise growth was correlated with the production of ephemeral vegetation, while accounting for size, sex, and repeated measurements of the animals as well as the interval between measurements. However, the production of ephemeral plants was likewise highly correlated with winter rainfall. Stochastic predation events between 2003 and 2007 decimated this cohort of tortoises. The average age of the long-term surviving tortoises from this cohort was 43 yr with a range of 39–47 yr. Twelve of the tortoises survived to the age of 39 yr and 11 of the 12 reached 40 yr.