In view of the paucity of detailed information in the literature relevant to the upper digestive tract of the Nile crocodile, this study describes the morphological and histological features of the oral cavity (gingivae, palate and tongue), pharyngeal cavity and oesophagus of the Nile crocodile, Crocodylus niloticus (Laurenti, 1768) using light microscopy. The findings, which were supplemented by scanning electron microscopy, were compared with published information. The ciliated component of the oesophagus was also examined using transmission electron microscopy. The oral cavity had the form of a triangle and was dorso-ventrally flattened. The dorsal limit was formed by the palate and the ventral limit by the broad-based tongue. The close proximity of the tongue and palate severely limited the space within the cavity. The caudal border of the cavity was formed by the dorsal and ventral components of the gular valve. The epithelium of the palate, gingivae and tongue was stratified squamous in nature and appeared lightly keratinised. Specialised epithelial structures in the palate, gingivae and tongue, revealed by both light microscopy (LM) and scanning electron microscopy (SEM), bore characteristics resembling structures responsible for pressure and taste reception. Glandular tissue in the tongue was arranged in a triangular formation in the posterior region and displayed morphological features ascribed to salt secreting glands described in other Crocodilia. There were no palatine glands in the oral region of the palate, except that the oral surface of the dorsal gular fold contained branched tubular mucus secreting glands. The pharyngeal cavity was also dorso-ventrally flattened and was bordered rostrally by the flaccid dorsal gular fold, which displayed a median apical notch, and the ventral gular fold, which was supported internally by the broad rostral tip of the basihyal plate (hyaline cartilage). In the occluded mouth, the dorsal gular fold and the more rostrally positioned ventral component of the gular valve isolated the pharyngeal cavity. This arrangement is essential in preventing the crocodile from drowning (flooding of the pharyngeal cavity) while capturing prey. The roof of the pharyngeal cavity was characterised by the opening to the internal nares (an extension of the nasal passage from the external nares), the fibrous Eustachian plug sealing the common opening to the paired Eustachian ducts and a nodular tonsillar region, which was situated caudo-laterally to the Eustachian plug. Throughout this region, the epithelium was typically ciliated with goblet cells. However, the tonsillar nodules displayed regions of partial or no ciliation on their surface. SEM and stereomicroscopic observations showed fine longitudinal mucosal folding throughout the pharynx the distension of which, together with the large capacity for mucus production (produced by intraepithelial glands and mucus secreting glands), would facilitate the swallowing of large chunks of food in the living state. The ventrally situated laryngeal mound containing the slit-like glottis also displayed longitudinal folds and a ciliated epithelium. Anatomically, the oesophagus could be divided into two clear regions. The cranial, approximate two-thirds appeared broad and flabby. At the tracheal bifurcation, the oesophagus narrowed significantly and indicated a greater muscular content, confirmed by light microscopy. LM and SEM examination of the oesophagus, however, revealed three regional components, viz., the cranial, mid- and caudal regions. In the cranial region, the epithelium was densely ciliated with intervening goblet cells being present. In the mid-region the ciliated component decreased with a concomitant increase in the goblet cell component. In the caudal region there was a further decrease in the number of ciliated cells and a higher concentration of goblet cells. Transmission electron microscopy (TEM) of the ciliated component of the oesophagus showed typical ultrastructural features of both the ciliated and goblet cells. / Dissertation (MSc (Veterinary Science))--University of Pretoria, 2002. / Anatomy and Physiology / unrestricted

Text in English / Ruti dam is located on the Nyazvidzi river, and is home to many Nile crocodiles (Crocodylus niloticus), which rely on fish and livestock for food. The community also relies on the dam and riverine for its resources. The investigation of crocodile impacts on humans and livestock, the trends and seasonality of attacks and identification of other predators resulted in formulation of research. The field interviews, using a structured questionnaire, field observation and focused group discussions were mainly used in data collection. Threats posed by crocodiles were identified as mainly human and livestock depredation, which has increased since the introduction of the crocodiles into the dam. The crocodile depredation varies between seasons, due to differences in water levels in the dam, and availability of alternative water sources. The attacks were mostly during the dry season and at the beginning of the wet season, when there were fewer water sources and when the water was dark and murky. The study assessed the human-crocodile conflict situation, based on interviews with the local residents and focused group discussions with fishermen. The conflict arose with livestock farmers after animal kills and fishermen, in cases of death, injury or damage to fishing gear. The killing of either humans or livestock was during the early hours of the day. Hostile attitudes of the residents towards crocodiles were high (83.9%). The majority, given the chance to eliminate the crocodile, would do so mercilessly. These negative attitudes can only be ameliorated when the damage is adequately compensated. The absence of compensation has increased the conflict, though no retaliation is taken against the crocodiles. The crocodiles prefer cattle in their kills (41% and 48%), followed by goats (38% and 25%), and, lastly, humans, in Buhera Rural District Council (BRDC) and Gutu Rural District Council (GRDC), respectively. Livestock farmers who stay close to the dam and Nyazvidzi suffer more losses, as their animals are more oftenly exposed to the dangers of crocodile predation, than those of farmers who stay far away, as they can use alternative water sources, and their animals are less likely to be exposed to the dangers of the crocodiles. The settlement pattern in BRDC has had an influence on predation. The farmers have also developed new livestock management techniques to reduce the loss of livestock. The fishermen suffer net damage on most occasions of their fish catches, as the crocodile might have learnt to follow the plastic floats on the water for easier prey from the nets. The fishing strategies have been developed to reduce fish loss. The death of fishermen is mostly that of people who enter the dam without canoes; no deaths were recorded of fishermen in canoes. Also, no capsizing of canoes has been recorded in Ruti dam, as fishermen always move in groups. Attacks in the Nyazvidzi River were on women and schoolchildren. Hyenas, as with the crocodile, have contributed to high kills of livestock (71.1%) and human kills were also reported in 2012 and July 2013. Though conflicts exist in the area, recommendations were made which might help to lower the conflicts. Educational campaigns and direct incentives from predator losses were identified as the main factors in conflict resolutions. The information on the importance of the predators and how or when it kills should be taught to respondents as they will be able to protect their livelihood. / Environmental Sciences / M. Sc. (Environmental Management)

Text in English / Ruti dam is located on the Nyazvidzi river, and is home to many Nile crocodiles (Crocodylus niloticus), which rely on fish and livestock for food. The community also relies on the dam and riverine for its resources. The investigation of crocodile impacts on humans and livestock, the trends and seasonality of attacks and identification of other predators resulted in formulation of research. The field interviews, using a structured questionnaire, field observation and focused group discussions were mainly used in data collection. Threats posed by crocodiles were identified as mainly human and livestock depredation, which has increased since the introduction of the crocodiles into the dam. The crocodile depredation varies between seasons, due to differences in water levels in the dam, and availability of alternative water sources. The attacks were mostly during the dry season and at the beginning of the wet season, when there were fewer water sources and when the water was dark and murky. The study assessed the human-crocodile conflict situation, based on interviews with the local residents and focused group discussions with fishermen. The conflict arose with livestock farmers after animal kills and fishermen, in cases of death, injury or damage to fishing gear. The killing of either humans or livestock was during the early hours of the day. Hostile attitudes of the residents towards crocodiles were high (83.9%). The majority, given the chance to eliminate the crocodile, would do so mercilessly. These negative attitudes can only be ameliorated when the damage is adequately compensated. The absence of compensation has increased the conflict, though no retaliation is taken against the crocodiles. The crocodiles prefer cattle in their kills (41% and 48%), followed by goats (38% and 25%), and, lastly, humans, in Buhera Rural District Council (BRDC) and Gutu Rural District Council (GRDC), respectively. Livestock farmers who stay close to the dam and Nyazvidzi suffer more losses, as their animals are more oftenly exposed to the dangers of crocodile predation, than those of farmers who stay far away, as they can use alternative water sources, and their animals are less likely to be exposed to the dangers of the crocodiles. The settlement pattern in BRDC has had an influence on predation. The farmers have also developed new livestock management techniques to reduce the loss of livestock. The fishermen suffer net damage on most occasions of their fish catches, as the crocodile might have learnt to follow the plastic floats on the water for easier prey from the nets. The fishing strategies have been developed to reduce fish loss. The death of fishermen is mostly that of people who enter the dam without canoes; no deaths were recorded of fishermen in canoes. Also, no capsizing of canoes has been recorded in Ruti dam, as fishermen always move in groups. Attacks in the Nyazvidzi River were on women and schoolchildren. Hyenas, as with the crocodile, have contributed to high kills of livestock (71.1%) and human kills were also reported in 2012 and July 2013. Though conflicts exist in the area, recommendations were made which might help to lower the conflicts. Educational campaigns and direct incentives from predator losses were identified as the main factors in conflict resolutions. The information on the importance of the predators and how or when it kills should be taught to respondents as they will be able to protect their livelihood. / Environmental Sciences / M. Sc. (Environmental Management)

In general Nile Crocodile Crocodylus niloticus numbers in South Africa appeared to have recovered after persecution and eradication attempts during the last century. Within the last decade, however, the future of South Africa’s Nile Crocodiles seems ominous yet again, as they are faced with renewed threats including habitat destruction and/or degradation. The primary Nile Crocodile populations in South Africa, Kruger National Park, Lake St Lucia and Ndumo Game Reserve are all currently threatened as a result of anthropogenic actions. The vulnerability of South Africa’s major Nile Crocodile populations has highlighted the need for further studies on and assessment of other populations in the country. This study was conducted from April 2009 to July 2010 on the Nile Crocodile population found in Pongolapoort Dam. The aim of the study was to obtain baseline data on the ecology of this previously unstudied population, which included obtaining an estimate of population size and structure, the reproductive dynamics and success of the population, general distribution of the population in the dam and seasonal changes in their distribution. The impact of the impoundment on this population was also discussed. Initial surveys from 1981 and 1989 described few crocodiles in the system. Currently Pongolapoort Dam contains a significant Nile Crocodile population that was previously not considered as substantial. A conservative estimate of 273 Nile Crocodiles was determined for Pongolapoort Dam in 2009-2010. A combination of survey methods allowed for a population structure to be gauged and identified as having 116 juveniles (< 1.2 m), 75 sub-adults (1.2 - 2.5 m), and 82 adults (> 2.5 m). Currently the population has a high percentage of juveniles (42 %), suggesting a growing population, with the proportion of adults (30 %) able to sustain a viable population into the future. From the construction of the Pongolapoort impoundment in 1972 the water level has fluctuated and the surrounding landscape has been altered. As a result the Nile Crocodiles residing in the area had to adapt to the ever changing environment. Their general distribution changed after dam wall completion, when the dam began to fill. First distributional change was a movement out of the gorge section into the newly flooded areas. After the Domoina floods (1983) the dam level rose by over 70 % and the crocodiles moved into the current inlet section. The majority of the crocodile population is now found in the inlet section of the Pongolapoort Dam, utilizing the Phongola River in summer months and residing in the inlet section as historical basking sites during the winter months. Investigating reproductive ecology is essential in order to access the population dynamics of an unstudied population, as reproductive output can be a measure of population health. Reproduction and nesting of Nile Crocodiles in Pongolapoort Dam, and in particular determining the effects of the impoundment on these were investigated. No previous reproductive effort had been documented prior to this study. Crocodiles congregated at a major basking site, where the Phongola River entered the dam, during August 2009 with a 576 % increase in numbers. This signalled the commencement of the breeding season. Females with transmitters made short trips upstream during this time. In November, with the first rains, the river rose and the majority of crocodiles moved up the inlet, and females established nests. Three major nesting areas were identified, two of which were located in the river inlet to the dam. Approximately 30 nesting females were identified during the 2009/2010 nesting season. All nesting areas identified had been used in prior nesting seasons. Nests were located on a variety of substrate types, from clay formed through culluvial and fluvial deposits to course river sand. Several of the nests were predated by Water Monitor (Varanus niloticus). Although the number of nesting females was greater than expected, during the study period there was a total recruitment failure of nests along the river due to a flash flood of the Phongola River in January 2010, destroying all nests prior to hatching. As several juvenile crocodiles were found during surveys, this preliminary study suggests that the Pongolapoort Dam Nile Crocodile population has a relatively high potential reproductive out-put, although their annual successes may vary greatly because of loss of nesting sites because of water level fluctuations and predation. It appears that the impoundment has generally had a positive impact on this Nile Crocodile population recruitment although suitable nesting sites may become limited. There appear to be no current threats to the Nile Crocodile Pongolapoort Dam population, however illegal gill-netting and poaching on the dam and surrounding reserves is on the rise and if not prohibited can result in future problems. A second concern is the high abundance of alien invasive plants that dominate the area, most notably in the river inlet section, the Nile Crocodiles main nesting area. The water quality entering the system is unknown at present and should be tested in future studies to assess whether there may be any reason for concern. In general the Nile Crocodile population in Pongolapoort Dam appears to be one of the least vulnerable and most reproductively successful in South Africa at present. The population has increased dramatically as a result of successful reproductive output even with the ecosystem changes as a result of the impoundment of the Phongola River. It is unlikely that the population increase was as a result of immigration from surrounding areas as the dam wall is a substantial barrier between the dam and the lower crocodile population of Ndumo Game Reserve some 70 km downstream. The high number of crocodiles found through all size classes, juveniles to large adults, also suggests that this population has been stably increasing for a number of years and has a sustainable breeding population. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2010.

Since 2008, large numbers of Nile crocodile (Crocodylus niloticus) carcasses were found in the Kruger National Park (KNP), South Africa. Most of the crocodile carcasses were found in the Olifants Gorge, which is situated below the Letaba and Olifants river confluence, before the Mozambique border and Massingir Dam. The Massingir Dam is an important resource and it plays a significant role in the welfare of the local Mozambican population. Autopsies performed on the crocodiles indicated that the adipose tissue colour changed from normal white to yellow and this is usually a sign of pansteatitis. Pansteatitis is caused by lipid peroxidation in an organism and it is characterised by the lack of vitamin E. This disease is recognisable by the hardening of the fatty tissue and yellow discolouration, and is mostly associated with aquatic organisms from polluted ecosystems. There are speculations that the crocodile fatalities may be associated with the Massingir Dam that backed up into the Olifants Gorge after flooding. After the dam was reconstructed, it flooded the Olifants Gorge, causing it to act like a localised sediment trap as the water flow slowed down and as a result, caused pollutants to build-up. Sediment samples were collected from selected rivers and ponds within the KNP. These samples were analysed for selected elements, persistent organic pollutants (POPs), and polycyclic aromatic hydrocarbons (PAHs). The sediment samples were analysed in Norway for POPs and PAHs with the use of a high-resolution gas chromatography/mass spectrometry (GC/MS) and the heavy metals were analysed in South Africa with the use of inductively-coupled plasma mass spectrometry (ICP/MS). In order to identify which elements may have affected the health of the crocodiles, a series of sediment quality indices were used. These indices made it possible to determine which elements may have been involved. The order of probability of heavy metals causing harm was Se>As>Ni>Cr>Cu>I>V>Mn>Co>Fe>Cd>Hg>Zn>Pb>Ba>U. The data was compared to selected international guidelines. All the information was used to determine which of the sampled sites had the highest contamination. The sites sampled with the highest concentrations were in the Crocodile, Nkomati, Olifants, and Letaba Rivers. Concentrations of the elements, POPs, and PAHs were also quantifiable in the Olifants Gorge. The following elements (Fe, Co, Cu, Cr, Pb, V, As, and Ni) were quantified at elevated levels and may therefore have caused negative effects on the crocodiles in the Olifants Gorge. These elevated concentrations, in combination with the dramatic change in the physical environment due to the dam, could have added additional stress that may have contributed to the observed crocodile mortalities in the Olifants Gorge. / MSc (Environmental Sciences), North-West University, Potchefstroom Campus, 2015

Since 2008, large numbers of Nile crocodile (Crocodylus niloticus) carcasses were found in the Kruger National Park (KNP), South Africa. Most of the crocodile carcasses were found in the Olifants Gorge, which is situated below the Letaba and Olifants river confluence, before the Mozambique border and Massingir Dam. The Massingir Dam is an important resource and it plays a significant role in the welfare of the local Mozambican population. Autopsies performed on the crocodiles indicated that the adipose tissue colour changed from normal white to yellow and this is usually a sign of pansteatitis. Pansteatitis is caused by lipid peroxidation in an organism and it is characterised by the lack of vitamin E. This disease is recognisable by the hardening of the fatty tissue and yellow discolouration, and is mostly associated with aquatic organisms from polluted ecosystems. There are speculations that the crocodile fatalities may be associated with the Massingir Dam that backed up into the Olifants Gorge after flooding. After the dam was reconstructed, it flooded the Olifants Gorge, causing it to act like a localised sediment trap as the water flow slowed down and as a result, caused pollutants to build-up. Sediment samples were collected from selected rivers and ponds within the KNP. These samples were analysed for selected elements, persistent organic pollutants (POPs), and polycyclic aromatic hydrocarbons (PAHs). The sediment samples were analysed in Norway for POPs and PAHs with the use of a high-resolution gas chromatography/mass spectrometry (GC/MS) and the heavy metals were analysed in South Africa with the use of inductively-coupled plasma mass spectrometry (ICP/MS). In order to identify which elements may have affected the health of the crocodiles, a series of sediment quality indices were used. These indices made it possible to determine which elements may have been involved. The order of probability of heavy metals causing harm was Se>As>Ni>Cr>Cu>I>V>Mn>Co>Fe>Cd>Hg>Zn>Pb>Ba>U. The data was compared to selected international guidelines. All the information was used to determine which of the sampled sites had the highest contamination. The sites sampled with the highest concentrations were in the Crocodile, Nkomati, Olifants, and Letaba Rivers. Concentrations of the elements, POPs, and PAHs were also quantifiable in the Olifants Gorge. The following elements (Fe, Co, Cu, Cr, Pb, V, As, and Ni) were quantified at elevated levels and may therefore have caused negative effects on the crocodiles in the Olifants Gorge. These elevated concentrations, in combination with the dramatic change in the physical environment due to the dam, could have added additional stress that may have contributed to the observed crocodile mortalities in the Olifants Gorge. / MSc (Environmental Sciences), North-West University, Potchefstroom Campus, 2015

Thesis (PhD (Conservation Ecology and Entomology))--Stellenbosch University, 2008. / The Okavango Delta, Botswana, is a unique ecosystem and this is reflected in its extraordinary biodiversity. The Nile crocodile (Crocodylus niloticus Laurenti) is the apex predator, and performs a number of vital functions in this system, making it a keystone species. The panhandle crocodile population has declined significantly over the last 80 years and is now threatened as a result of past over-exploitation and present human disturbance. In order to effectively conserve this species and in turn the health of this important region it is imperative to gain an understanding of their ecology and population dynamics. The population status of the Nile crocodile in the panhandle region of the Okavango Delta, Botswana, was assessed using a combination of capture-mark-recapture surveys, spotlight surveys and aerial surveys. The capture-mark-recapture experiment was conducted continuously from 2002 - 2006. A total of 1717 individuals, ranging in size from 136 mm – 2780 mm SVL, were captured, of which 224 animals were recaptured. Using a Bayesian technique, the total annual population in the panhandle region of the Okavango Delta was estimated to be 2 570 ± 151.06 individuals, with an adult population of 649.2 individuals with the number of breeding females estimated to be 364 individuals. It was concluded that this population cannot sustain the further harvest of breeding animals prior to the increase and stabilization of the population. Spotlight counts revealed a decline in the encounter-rate of crocodiles on the Okavango River with time, although more long-term data needs to be collected to confirm this trend. During the low-water season (September - February), 22.34 % of all crocodiles were observed, while during the flood-season only 13.34 % were observed, yielding correction factors for spotlight surveys of 4.46 (low-water) and 7.49 (high-water) for all animals in the panhandle. Two aerial surveys, conducted at the low-water and high-water peaks yielded total estimates of 588 (77.7 % of adults) during the low-water period and 350 (56.7 % of adults) during the high-water period. Correction factors of 1.28 (low-water) and 1.77 (high-water) were calculated for aerial surveys. An annual average of 50 nests was located in the panhandle, representing a 50 - 60 % decrease over the last 20 years. In regions with high human disturbance, breeding females situated their nests in hidden locations, away from accessible channels. Hatchlings exhibited elongation of the jaw in order to capture smaller prey items and morphometric shifts in jaw shape coincided with a dietary change at 400 mm SVL. The jaw became broader and deeper as animals matured, presumably in preparation for larger mammalian prey. The average growth rate of recaptured yearlings was 0.198 ± 0.116 mm.d-1 SVL and was closely correlated to the amount of time an individual spent in above-average water temperatures. Body condition (RCF) was significantly and positively correlated with a rise in water-level and negatively correlated to time spent in above-average water and air temperatures. Average RCF values were intersected when animals had spent 50 % of their time in above-average temperatures and water level. Generally crocodiles in the panhandle showed no significant sex-related differences in their sizes or the distances they travelled. The majority of recaptures (62.5 %) moved less than 500 m from the initial capture site. Adults in the panhandle occupied definite ranges, within which were preferred core areas where the majority of their time was spent. The panhandle crocodile population has declined significantly over the last 80 years, and is now threatened as a result of past over-exploitation and present human disturbance. The management of this population, including both its conservation and sustainable commercial utilisation, requires an adaptive strategy based on accurate monitoring procedures.

Thesis (MSc(Conservation Ecology and Entomology)--University of Stellenbosch, 2006. / The stomachs of 286 crocodiles (17 cm to 166 cm snout to vent length) were lavaged over a two year period. Crocodylus niloticus has a similar ontogenetic shift in diet to that of other crocodilians. Yearlings predated primarily on aquatic insecta and arachnida, as crocodile size increased (juveniles) the diet became more diverse including crustacea, amphibia and fish. The largest size class (sub-adults) consumed primarily fish. Yearlings fed consistently throughout the year, however a higher proportion of empty stomachs occurred within the juvenile and sub-adult size classes during the winter months. A captive experiment with wild caught crocodiles (0.7 kg - 20 kg) indicated a decrease in satiation rate (maximum mass of food eaten as a percentage of crocodile body mass) from 11.3 % to 6.5 % with an increase in crocodile size. Wild yearlings consumed 0.48 % of their body mass in prey per day, and juveniles, 0.23 %. The wild food conversion rates of natural prey were low, 32 % and 40 % for yearlings and juveniles respectively. This was possibly due to a high percentage of indigestible (chitinous) invertebrate mass in the diet. The percentage of stomach stone mass to crocodile body mass increased with crocodile size. Seven species of nematodes were found within the stomachs, four of which represent new geographic records.

Thesis (MA (Geography and Environmental Studies))--University of Stellenbosch, 2006. / The Okavango river along the panhandle of the Delta, in Botswana, is home to many wildlife species as well as to many large village communities. Local communities rely on the riverine system and its resources for subsistence and commerce. Activities associated with the utilization of these resources are governed by the fluctuating water levels of the river, which inhibit access during high water levels and allow access during low water levels. The high intensity of activities, such as reed harvesting, fishing and increased tourism, during low water periods coincides with the breeding season of many wildlife species in the system, including the Nile crocodile (Crocodylus niloticus). Over 90% of crocodile breeding areas in the Delta are found only in the panhandle region. The association between the intensity of human activities in the floodplains and crocodile nesting activity means that much of the habitat required for nesting is vulnerable to human disturbance and this could have severe negative impacts on the future of the Okavango crocodile population. The study evaluated habitat vulnerability by mapping and spatially comparing habitat suitability, based on optimum environmental requirements for crocodile nesting, and human disturbance factors. A detailed crocodile nesting survey was carried out to locate and test all nesting sites according to criteria selected by species experts. The results from the survey were used to locate suitable nesting habitat in the study area by analysis in a Geographic Information System (GIS). Disturbance factors were visually identified and their locations in the study area spatially mapped. Their spatial influences on crocodile nesting were used as factors in a Multi-Criteria Evaluation (MCE) that evaluated the combined effect of the disturbances on the area defined as suitable crocodile habitat. The results indicate the extent of habitat vulnerable to human disturbances. The results from the study show that 59% of once suitable crocodile habitat is currently disturbed by human activities. Most of the remaining 41% of undisturbed habitat is located along the Moremi/Phillipa side channel, which represents a core area for protection measures to be instated. The study recommends the declaration of a crocodile nesting sanctuary in this side channel to ensure the breeding success of this keystone species.