Growth and maturity of the gopher tortoise in southwestern Georgia

Abstract

Growth rates of gopher tortoises (Gopherus polyphemus) were determined by measuring individuals during two consecutive years and by correlating plastral annuli counts and measurements with shell dimensions. Ninety-three percent of growth occurred from April-October. The annual increment in carapace length (CL) for immatures was 11-12 mm; this varied by CL class. Growth increments were greatest for specimens 100-190 mm CL (about 4-11 yr of age), and gradually decreased thereafter. However, body volume increments peaked as tortoises grew from 220-230 mm CL, shortly before attainment of somatic maturity. Sexual maturity typically occurred at age 16-18 years (230-240 mm CL) in males and at 19-21 years (250-265 mm CL) in females. Thereafter, growth in both sexes was reduced, but females grew at greater rates and became significantly larger. Development of tortoises living in sand ridge habitats in southwestern Georgia was much slower than in Florida: maturity was delayed about 7 years. Growth was influenced by habitat quality, ambient temperature, and length of the annual activity season. The extended period of time required for attainment of maturity is potentially a limiting factor in population growth, and becomes more important in the northern portions of the species' range.