Abstract
Natrix natrix is, together with N. tessellata, the only representative of water snakes found in Iran. The lack of ecological studies on this species in Iran stimulated the current preliminary research on some basic biological traits. From April to July 2008, a total of fifty five snakes were collected from two stations in the southern part of the Caspian Sea coast, Iran: Gomishan Wetland and Sari. Basic morphometrics were compared between sexes and stations and gonadal development was compared between stations and seasons. At the two stations, adult sex ratio was not different from 1:1 and juveniles composed a predominant portion of the sample. Both sexes had unimodal length class size with a peak at 40-45 cm snout-vent length (SVL). Body sizes were unusually small for the species and no SVL sexual dimorphism was detected although males were relatively heavier than females for the same SVL. Snakes of both sexes attained larger size with better body condition at Sari than in Gomishan. Males and females carried more mature gonads in summer. However, in Sari males developed relatively larger testes earlier in the season and both sexes displayed less synchronic reproduction at this station. These results are best explained by local variations in habitat, trophic availability and degree of environmental disturbance.
