Twenty-Third Annual Meeting and Symposium of the
Desert Tortoise Council, April 3-5, 1998
Abstracts

Growth was monitored on 127 tortoises in an eastern Mojave Desert population from 1988 to 1995. Nearly all annual growth occurred between early April and mid-June. Smaller tortoises had a larger growth rates. Between 125 and 184 mm in carapace length, the mean growth rates was 10.80 mm ± 0.660. Above 184 mm, growth rates decreased in a more-or-less linear fashion until tortoises reached approximately 235 mm (males) or 208 mm (females), at which point growth was less than 2 mm per year. For females, this growth cessation point was coincident with increased reproductive output. Both among and within gender, the larger size that a tortoise obtains, the greater its growth rate at some point. There was no significant difference in growth between immature males and females, but adult males experienced significantly higher growth rates than adult females, following a growth spurt at supposed sexual maturity. Drought negatively affected growth in all groups. For immature tortoises, mean growth in the best years was 14.7 mm, but only 3.6 during a drought; for adults, growth was negligible during drought. Age was predicted from size using von Bertalanffy growth curves.