Learning from the Wild: Status of the Introduced Pancake Tortoise Malacochersus tornieri Population in Tsavo East National Park, Kenya

Abstract

Abstract. In April 2001, 187 illegally collected and confiscated pancake tortoises (Malacochersus tornieri) were released in Mzinga and Irima rocky hills in the southern part of Tsavo East National Park, an area where there were no free-ranging wild populations. The aim of this study was to establish the status of this introduced population and identify the lessons that can be learned to guide future reintroductions. Prior to release, the specimens were marked by cutting numbered notches on the marginal scutes based on a coding system. In June 2022, a revisit to the April 2001 release sites was done to retrace this population in an effort to both recapture some of the individuals or find a new juvenile cohort. After 21 yrs, only 15 individuals were found—10 of which were recaptures, representing 5.3% of the total release population. Of these 10 recaptures, only 2 had clear marks and could be traced to a specific number that showed they were mature adults when released. The 8 recaptured tortoises did not have marks and their carapaces were either worn out to plain brownish or had faded dark marks. It was assumed that these were likely those young specimens released with a carapace length of less than 130 mm and that the notch mark disappeared during body growth. Using a combination of the carapace length, carapace color pattern, and absence of notch marks, 5 specimens were confirmed to have been born after the initial release, representing a new cohort. Pancake tortoise carapace growth in captivity has been found to be very fast, and specimens reach sexual maturity at 150 mm and in about 6 yrs, and after this no significant carapace growth occurs. This fast growth rate is not possible in the wild, where there are long periods of inactivity during the dry season. Hence, it is assumed that growth in captivity should be twice or thrice that in the wild. Therefore, using our data from new and recaptured tortoises, and comparing it with the growth rate and color change in captive specimens, it is possible to estimate the age of wild individuals. This study also shows that there is carapace color and pattern change with carapace growth with age, until a time when the color pattern starts fading with little or no change in carapace length. The study found only a very small proportion of the total number of individuals released. This could be attributed to the fact that the majority of the individuals (82.9% being mature adults, > 130 mm) were about 15–20 yrs old, and 21 yrs later they likely would have naturally died after exceeding their lifespan of about 25 yrs. Others may have died of predation before breeding. What is clear is that, despite the low number of encountered individuals from new cohorts, reintroduction of confiscated tortoises is a viable initiative to boost depleted wild populations. Finally, given that there are viable populations at captive breeding facilities, it is highly recommended that the international pet trade should focus on getting captive-bred specimens and leave the wild ones to boost local tourism.