Rediscovery of relict populations of the Nile crocodile <i>Crocodylus niloticus</i> in south-eastern Mauritania, with observations on their natural history

Shine, Tara; Böhme, Wolfgang; Nickel, Hemmo; Thies, Dirk F.; Wilms, Thomas

doi:10.1046/j.1365-3008.2001.00187.x

Cited by 13 publications

(11 citation statements)

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“…In contrast to other African regions, villagers from Mauritanian mountains peacefully accept crocodile presence in gueltas [8], [9], [60], [78] and even consider their potential for local economy by launching crocodile-watching activities [60]. Moreover, C. suchus in Mauritania constitutes a good candidate umbrella species, since it's conservation is tied to other aquatic or semi-aquatic organisms (e.g.…”

Section: Discussionmentioning

confidence: 99%

Should I Stay or Should I Go? Dispersal and Population Structure in Small, Isolated Desert Populations of West African Crocodiles

2014

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The maintenance of both spatial and genetic connectivity is paramount to the long-term persistence of small, isolated populations living in environments with extreme climates. We aim to identify the distribution of genetic diversity and assess population sub-structuring and dispersal across dwarfed desert populations of Crocodylus suchus, which occur in isolated groups, usually less than five individuals, along the mountains of Mauritania (West Africa). We used both invasive and non-invasive sampling methods and a combination of mitochondrial DNA (12 S and ND4) and microsatellite markers (32 loci and a subset of 12 loci). Our results showed high genetic differentiation and geographic structure in Mauritanian populations of C. suchus. We identified a metapopulation system acting within four river sub-basins (high gene flow and absence of genetic structure) and considerable genetic differentiation between sub-basins (F ST range: 0.12–0.24) with rare dispersal events. Effective population sizes tend to be low within sub-basins while genetic diversity is maintained. Our study suggests that hydrographic networks (temporal connections along seasonal rivers during rainy periods) allow C. suchus to disperse and maintain metapopulation dynamics within sub-basins, which attenuate the loss of genetic diversity and the risk of extinction. We highlight the need of hydrographic conservation to protect vulnerable crocodiles isolated in small water bodies. We propose C. suchus as an umbrella species in Mauritania based on ecological affinities shared with other water-dependent species in desert environments.

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Section: Discussionmentioning

confidence: 99%

Should I Stay or Should I Go? Dispersal and Population Structure in Small, Isolated Desert Populations of West African Crocodiles

2014

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“…Several scientific expeditions to Mauritania were developed from 2000 onwards [27]–[31] which reported the presence of crocodiles in three southern Mauritania massifs: Tagant, Assaba and Affolé (Figure 1). Populations are best known in the Gabbou basin, on the northern face of the Tagant mountains, where they are present in 26 isolated localities [29], [31].…”

Section: Introductionmentioning

confidence: 99%

“…But outside this river basin, knowledge on distribution is scarce. In the Affolé, crocodiles are known from four localities [27], [28], and in the Assaba, references date from before the 1970s [18], [32]–[34]. In the Tagant, crocodiles are mostly found in two major habitat types [29]–[31]: 1) rocky pools, locally known as guelta , generally located upstream of narrow valleys at the base of the mountains.…”

Section: Introductionmentioning

confidence: 99%

“…The size of gueltas varies according to the geomorphology of mountain slopes but generally are small, ranging between 0.001 ha and 1.0 ha; and 2) floodplains, locally known as tâmoûrt , located on the foothills of the mountains, which are larger in size and reach frequently more than 1,000 ha. Nevertheless, water is usually shallow and tâmoûrts are mostly arid during the dry season (October to June), thus crocodiles are forced to find shelter in nearby rock outcrops during this period [27], [30]. Despite the recognized importance of gueltas and tâmoûrts for the persistence of populations in the Tagant, little is known about occupied habitats in the Affolé and Assaba where crocodiles have been suggested to use distinct habitats, such as rivers (locally known as oued ), lakes and dams [29], [32].…”

Section: Introductionmentioning

confidence: 99%

“…Crocodile populations in Mauritania are fragmented and many are constituted by a small number of individuals [27], [29]–[31], [35]. Estimates are mostly restricted to the Tagant, where one to three individuals where mentioned in small sized gueltas [31] and one to eight individuals in eight gueltas of the Krâa Naga river [29].…”

Section: Introductionmentioning

confidence: 99%

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

Brito

Martínez‐Freiría

Sierra³

et al. 2011

PLoS ONE

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BackgroundRelict populations of Crocodylus niloticus persist in Chad, Egypt and Mauritania. Although crocodiles were widespread throughout the Sahara until the early 20th 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 FindingsA 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/SignificanceResearch 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.

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Analyzing the Life History of Caimans: The Growth Dynamics of Caiman latirostris From an Osteohistological Approach

Eugenia,

Bona,

Siroski

et al. 2024

Journal of Morphology

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Skeletochronology and growth dynamics are intensively investigated in vertebrate osteohistology. These techniques are particularly important for interpreting the life history of long‐lived species, such as crocodilians. To understand the longevity, growth dynamics, sexual maturity, and sexual dimorphism of caimans we studied an almost complete ontogenetic series of captive and wild specimens of Caiman latirostris from different localities of Argentina. We identified both cyclical and noncyclical growth marks in juvenile caimans, and we suggest that the latter are associated with environmental stress. By overlapping the growth marks of different individuals, we were able to estimate the minimum age of each specimen. Variations in growth rate are evident in different bones, with the femur and scapula having the highest growth rates, while the fibula and pubis have much slower growth rates. We were able to determine the approximate age of sexual maturity from growth curves deduced from osteohistology, which concurred with those assessed in ecological studies. Additionally based on the growth curves we were able to document different growth dynamics which may be related to sexual dimorphism. This study provides valuable insights into the life history and ecological dynamics of crocodilians, shedding light on their growth patterns, attainment of sexual maturity, and the influence of environmental factors on growth. Furthermore it documents the intraspecific and interelemental osteohistological variation in crocodilians and has direct implications for studies that assess the life history of extinct archosaurs and other sauropsids.

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Rediscovery of relict populations of the Nile crocodile Crocodylus niloticus in south-eastern Mauritania, with observations on their natural history

Cited by 13 publications

References 1 publication

Should I Stay or Should I Go? Dispersal and Population Structure in Small, Isolated Desert Populations of West African Crocodiles

Should I Stay or Should I Go? Dispersal and Population Structure in Small, Isolated Desert Populations of West African Crocodiles

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

Analyzing the Life History of Caimans: The Growth Dynamics of Caiman latirostris From an Osteohistological Approach

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