Growth and population structure of the Moorish Tortoise ( Testudo graeca graeca) in Westcentral Morocco: possible effects of over-collecting for the tourist trade

Abstract

We studied growth of 284 live Moorish tortoises ( Testudo graeca graeca) from the central Jbilet Mountains, the Admine Forest, and near Essaouira in westcentral Morocco in 2001. Size structures, but not age structures, differed significantly among populations. No very old tortoises were found at any site. Most populations of tortoises suffered over-collecting for the tourist trade in the past, and some collecting still continues, which probably explains the lack of older tortoises. Of tortoises remaining in the populations we studied, both males and females grew relatively quickly for 10–12 yr in all three populations, after which their growth rates deceased markedly. Females in all three populations had greater asymptotic sizes than males, and CL and log mass differed significantly between sexes by age 9 yr for the three populations, except for log mass of tortoises from Essaouira, which differed by age 6. Mean CLs and log masses were significantly greater in Admine and Essaouira tortoises than in tortoises from Jbilet. Estimated mean age at maturity varied from 5.8 to 7.6 yr for males and 7.7–10.5 yr for females. Although past over-collecting of tortoises has probably depressed population abundances and eliminated the larger, older tortoises at all three sites, the current differences in population structure and growth pattern may be the result of geographic variation in environmental conditions, suggesting different selective mechanisms for the three populations.