Meeting Abstract
P1.15 Thursday, Jan. 3 Demography of two populations of Gopherus polyphemus:size, age, growth and habitat quality. CALLAWAY, J.C.*; ROSTAL, D.C.; MARLEY, P.H.; ENTZ, J.W.; Georgia Southern University; Georgia Southern University; Georgia Southern University; Georgia Southern University john_b_callaway@georgiasouthern.edu
Determination of age in adult tortoises has been difficult due to the lack of any distinct characteristics. Due to indeterminate growth in reptiles it is largely assumed that larger tortoises are older. This theory however does not take into account habitat quality and resource availability. It has been shown turtles and tortoises have annuli on the carapace and plastron scutes, which vary in size depending on the growing year (Kimmett, 2006). These may serve in aging tortoises up to a point, but are not useful once tortoises become sexually mature. In Gopherus polyphemus the method of counting annuli for aging is not accurate due to their burrowing instincts which causes shell wear. Adult size, shell wear and growth data were used to determine whether there were signs of indeterminate growth in two populations of G. polyphemus found on George L. Smith State Park and Fort Stewart Army Reserve, which differ in quality of habitat. Both populations have been studied since 1994 and have long-term recapture data. Shell wear was used to categorize individuals into estimated age groups. A rating system was developed based on the amount of annuli still visible on each scute which was measured as 0(no wear), 1(75-90% annuli present), 2(60-70% annuli present), and 3(<50% annuli present). For each tortoise captured, pictures and individual data was taken. Size and degree of shell wear were not correlated and support the conclusion that habitat quality and resource availability are important in determining the ultimate size of individuals, even species with indeterminate growth. Relationships between size, location and age based on shell wear provide insight into population structure, viability and recruitment.
