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, 6 (2), e14734

Crocodiles in the Sahara Desert: An Update of Distribution, Habitats and Population Status for Conservation Planning in Mauritania

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Crocodiles in the Sahara Desert: An Update of Distribution, Habitats and Population Status for Conservation Planning in Mauritania

José C Brito et al. PLoS One.

Abstract

Background: Relict populations of Crocodylus niloticus persist in Chad, Egypt and Mauritania. Although crocodiles were widespread throughout the Sahara until the early 20(th) century, increased aridity combined with human persecution led to local extinction. Knowledge on distribution, occupied habitats, population size and prey availability is scarce in most populations. This study evaluates the status of Saharan crocodiles and provides new data for Mauritania to assist conservation planning.

Methodology/principal findings: A series of surveys in Mauritania detected crocodile presence in 78 localities dispersed across 10 river basins and most tended to be isolated within river basins. Permanent gueltas and seasonal tâmoûrts were the most common occupied habitats. Crocodile encounters ranged from one to more than 20 individuals, but in most localities less than five crocodiles were observed. Larger numbers were observed after the rainy season and during night sampling. Crocodiles were found dead in between water points along dry river-beds suggesting the occurrence of dispersal.

Conclusion/significance: Research priorities in Chad and Egypt should focus on quantifying population size and pressures exerted on habitats. The present study increased in by 35% the number of known crocodile localities in Mauritania. Gueltas are crucial for the persistence of mountain populations. Oscillations in water availability throughout the year and the small dimensions of gueltas affect biological traits, including activity and body size. Studies are needed to understand adaptation traits of desert populations. Molecular analyses are needed to quantify genetic variability, population sub-structuring and effective population size, and detect the occurrence of gene flow. Monitoring is needed to detect demographical and genetical trends in completely isolated populations. Crocodiles are apparently vulnerable during dispersal events. Awareness campaigns focusing on the vulnerability and relict value of crocodiles should be implemented. Classification of Mauritanian mountains as protected areas should be prioritised.

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1
Figure 1. Distribution of crocodiles in North Africa.
Dots represent localities where crocodiles are currently present (present), where presence is possible but needs confirmation (possible), where crocodiles were extinct in the 20th century (extinct) or where crocodiles where present during the Holocene. Line represents the current northern limit of the range of continuous populations. Extinction localities georeferenced from , , , , –. Holocene localities georeferenced from , , , –. Possible and present localities from outside Mauritania georeferenced from , , , , , .
Figure 2
Figure 2. Distribution of crocodile localities along major river basins of southern Mauritania.
Dots represent localities where crocodiles are currently present (present), where presence is possible but needs confirmation (possible), where crocodiles were reported to be present but this study did not confirmed their presence (not confirmed) or where crocodiles went extinct (extinct). Easternmost known locality in Mauritania (locality 78) is only represented in small inset. Numbers refer to localities described in Table S2. Localities for Gabbou basin are shown in detail in Figure 3. Background is a composite Landsat image depicting land-cover.
Figure 3
Figure 3. Distribution of crocodile localities along the Gabbou river basin on Tagant mountains.
Dots represent localities where crocodiles are currently present (present), where crocodiles were reported to be present but this study did not confirmed their presence (not confirmed) or where crocodiles were found dead (found dead). Numbers refer to localities described in Table S2. Names represent major seasonal water lines flowing to the Gabbou lake. Background is a composite Landsat image depicting land-cover.
Figure 4
Figure 4. Examples of gueltas with presence of Nile crocodiles in Mauritania.
A. Tartêga; B. El Khedia; C. Garaouel; D. Oumm el Mhâr.
Figure 5
Figure 5. Examples of oueds, lakes and tâmoûrts with presence of Nile crocodiles in Mauritania.
A. oued Foum Goussas; B. lake Boû blei'îne; C. tâmoûrt Taghtâfet; D. tâmoûrt Bougâri.
Figure 6
Figure 6. Examples of Nile crocodiles from Mauritania.
A. juveniles at guelta Matmâta; B. adult killed at Dar-Salam village, near guelta Matmâta; C. the single adult at guelta El Khedia; D. sub-adult at guelta Garaouel; E. two adults hidden in a cave at 8 m depth in guelta Legleyta; F. adult killed near tâmoûrt Taghtâfet; G. basking adults at guelta Metraoucha; H. sub-adult inside a spring-fed water trough at Chegg el Mâleh surrounded by hundreds of frogs (Hoplobatrachus occipitalis).

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