Données préliminaires sur la taille, la croissance et la longévité du varan du Nil (Varanus niloticus) dans la région du lac Tchad

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Abstract
A sample of 288 Nile varanids, including only adults and subadults (153 males and 135 females), was collected in the Tchadian part of Lake Tchad where the species is regularly exploited. Each animal was measured (L, total length; MC, snout–vent length) and weighed, and its age was determined by the skeletochronological technique. No information of this sort, collected on a wide sample, was hitherto available. For the age-classes studied, the most representative sizes in the population (the medians being considered) were close to 155 cm for males and 134 cm for females, with respective masses of about 5 and 3 kg. The difference between sexes was highly significant. Conversely, age structure in the samples were not significantly different among sexes (except for one age-class: 4 years). The longevity of these lizards is about 8 years in the Lake Tchad region. The relationship between tail length and snout–vent length shows similar tendencies in both sexes (Q = 1.06MC + 21.48). The tail becomes proportionally shorter with growth. Both sexes also display similar tendencies for the relationship between total length and mass (M = 8.131E − 9L3.992 − 8.131E − 9(213..992) + 0.034). Body growth in the Nile varanids corresponds to a model derived from Von Bertalanffy's general model: L = K(1 − e−b(age)) + a. Growth of males is faster and steadier than that of females. Males reach their asymptotic size (207 cm) at a later age (9 years) than the females (154.8 cm reached at age 6 years). Though comparative data are very scarce, the growth rate in the animals examined seems high compared with that of other large species of varanids, especially Varanus komodoensis.

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