Population structure and body size of the Sahara blue-eyed pond turtle Mauremys leprosa saharica, from an isolated pond in the Lower Draa Basin, southern Morocco

Abstract

The marginal populations of the Sahara blue-eyed pond turtle, Mauremys leprosa saharica (Testudines: Geoemydidae) in the pre-Saharan area in the Lower Draa Valley, are faced to extreme environmental conditions of arid climate and anthropogenic activities including overuse of water and land salinization. In this study, we investigated a small isolated population of the blue-eyed pond turtle at Sidi El Mehdaoui Oasis, Lower Draa Valley, to determine its population structure and morphometric characteristics. Water salinity was about 24% of seawater and dissolved oxygen concentration was less than 3 mg l^-1 (sub-hypoxia). The average body size of adults (carapace length) was much lower in comparison to other Moroccan populations. Among adult individuals, the mean carapace lengths were 103 ± 21 mm and 104.4 ± 35 mm for males and females, respectively. The corresponding mean body mass were 173 ± 92.4 g and 135 ± 52 g. There were no significant differences between sexes for size or weight. The studied population is small, with a predominance of adults (75%). A significant sexual size dimorphism was found. In fact, the Sexual Dimorphism Index for size had the lowest level ever described for the species possibly because of the low productivity of this marginal isolated habitat. The increased drought and salinization are major threats to the long-term persistence of the vulnerable populations of the Saharan blue-eyed pond turtle and their habitats. Therefore, conservation measures of these populations through the protection of their habitats are very urgent.

Keywords: Body size; Mauremys leprosa saharica; Peripheral population; Population structure; Sahara desert.