Skeletochronology, Body Growth and Effectiveness of Growth Marks to Estimate the Ages of Sumatran Water Monitor Lizards (Varanus salvator macromaculatus) (Early view)

Abstract

Demand for water monitor lizards (Varanus salvator macromaculatus) from Sumatra and Kalimantan for the leather industry is the highest compared to varanid species from Java (V. s. bivittatus) or Sulawesi (V. s. ziegleri). No conclusive evidence on the age estimate of the individuals being harvested. The skeletochronology method was used to estimate harvested Sumatran water monitors’ age and body growth using fibular bones. The mid-diaphysis fibula bone cross-sections of 81 individuals (39 females and 42 males) showed that the line of arrested growth  (LAG) was not always clearly visible. Periosteal bones in individuals with SVLs of 39.0-70.0 cm showed double and multiple LAGs and only a few individuals had apparent LAG. As the SVL increases, the double and multiple LAGs are not seen in individuals with more than 70 cm SVL. The estimated ages of harvested individuals of female V. s. macromaculatus with SVLs ranging from 40.1-71.0 cm were 2-3 years old, whilst for males with SVLs ranging between 39.0-96.0 cm, were 2-5 years old. A strong correlation between the SVL and fibular mid-diaphysis diameter was observed in both sexes. This indicates that the formation of LAGs occurs steadily every year, although LAGs are not always clearly visible in every individual, especially in young ones.