The Nile crocodile (Crocodylus niloticus) is one of 23 extant crocodilian species, and has been farmed in southern Africa since the 1960s. For the crocodile industry, chronic stress and its often negative consequences are a concern, since stressors can negatively affect animal production as well as the health of the crocodiles. When confronted with a stressor, an individual displays a stress response consisting of a suite of physiological and behavioral alterations to cope with the challenge. So far, however, no method for determining stress-related responses in Nile crocodiles has been established. In other crocodilians, the assessment of physiological responses to stress, like the related alterations in glucocorticoid concentrations, has already been done, but only by using an invasive approach, with the disadvantage of a possible handling-induced stress response. By establishing a non-invasive technique to monitor glucocorticoid levels in captive Nile crocodiles based on faecal hormone analysis, this study not only made an important contribution to a better understanding of stress and related hormonal changes in Nile crocodiles, but also provided a solid basis for developing similar non-invasive tools to collect information on the level of stress experienced by other crocodilians. Specifically the study aimed 1) to assess adrenocortical activity in Nile crocodiles by measuring faecal glucocorticoid metabolite (FGM) concentrations, and 2) to characterise changes in FGM levels in captive Nile crocodiles in relation to different housing conditions. An adrenocorticotropic hormone (ACTH) challenge was performed on 10 sub-adult crocodiles at Le Croc crocodile farm, South Africa, resulting in serum corticosterone levels of up to ~1200 %, 1 - 5 hours post-injection, above the pre-injection levels. An additional 8 individuals were exposed to electric immobilisation and handling only (control group), which resulted in a 20 – 2700 % elevation in serum corticosterone concentrations, indicating that handling was already a sufficient stressor. FGM levels in 3 singly housed animals (2 ACTH challenge; 1 handling only) reached peaks of 136 – 380 % above pre-injection levels at about 7 to 15 days following treatment, demonstrating that non-invasive hormone monitoring can be used for assessing adrenocortical function in captive Nile crocodiles based on FGM analysis. By assessing the impact of group size (n = 1, 2, or 4 individuals) on FGM levels, highest mean hormone values were found in the paired animals. A possible explanation for this finding could be that the necessary re-grouping for the study resulted in an unstable group composition, especially for the paired animals of similar size, which is reflected in comparable higher FGM concentrations. However, future research would be necessary to investigate this potential relationship in more detail. My study created opportunities to improve the management and welfare of farmed crocodiles in terms of more appropriate housing conditions and husbandry for these animals. Finally, the now established non-invasive method for monitoring adrenocortical function in Nile crocodiles provides a solid basis for further studies focusing on monitoring factors influencing adrenocortical function in populations of Nile crocodiles in the wild. / Dissertation (MSc)--University of Pretoria, 2012. / Paraclinical Sciences / unrestricted

Since the first report of Mycoplasma-associated polyarthritis in farmed Nile crocodiles in 1995, the disease has spread across Zimbabwe and South Africa and has resulted in significant economic losses on infected farms. Due to poor response to antimicrobial treatment and frequent relapses, the use of an autogenous vaccine to manage disease outbreaks was evaluated. Two previous trials had been performed with a similar vaccine and the results suggested that the vaccine could be effective in alleviating disease, although the numbers of animals were limited in both. This trial aimed to evaluate an inactivated, alum-adjuvanted M. crocodyli whole-cell vaccine in a large group of yearling crocodiles under field conditions on a farm in Zimbabwe where repeated M. crocodyli outbreaks have been reported. The safety of the vaccine was assessed by administrating the vaccine intraperitoneally to a subset of crocodiles. No adverse clinical reactions were observed in any of these crocodiles. A group of two thousand two hundred crocodiles received two intramuscular vaccinations four weeks apart in the autumn of 2011, while another group of two thousand two hundred crocodiles served as unvaccinated controls. Serum was collected from a subset of the vaccinated and unvaccinated crocodiles at different time-points before and after vaccination to evaluate the humoral response to vaccination. Latex slide agglutination tests (LAT) were performed on all samples and positive samples were titrated with the latex slide agglutination test and metabolism inhibition assay. A low percentage of sera were positive with serological tests done prior to vaccination, suggesting either circulating Mycoplasma or maternal immunity. Statistically significant increase in sero-positivity was detected with LAT four weeks after primary vaccination, although the titre remained low. Six weeks after the booster vaccination the percentage seropositive vaccinated crocodiles had decreased and there were no statistically significant difference between the percentage seropositive vaccinated and unvaccinated crocodiles. A significant outbreak of Mycoplasma-like polyarthritis was encountered 6 months after vaccination, in October 2011. Both vaccinated and unvaccinated crocodiles were affected. Serum samples from different subsets of crocodiles were collected and evaluated similar to the vaccine trial. The results indicated that a similar rate of sero-positivity was present in all crocodiles, irrespective of vaccination- or disease status Sera collected during this trial was used to evaluate the performance of the latex slide agglutination assay compared to the metabolism inhibition assay (“Gold standard” assay), as the performance of the LAT had not been evaluated previously. The calculated diagnostic sensitivity was 72%, diagnostic specificity was 32%, the predictive value of the positive test was 36% while the predictive value of the negative test was 69%. This trial indicated that the autogenous, inactivated, alum-adjuvanted, whole-cell vaccine against M. crocodyli was not able to protect farmed Nile crocodiles on an infected farm against clinical Mycoplasma-associated polyarthritis. It was also found that the latex slide agglutination assay could be useful as a robust, pen-side assay to evaluate exposure to M. crocodyli, although other assays, such as PCR, bacterial culture or growth inhibition assays, has to be performed to confirm the presence of disease. / Dissertation (MSc)--University of Pretoria, 2012. / Veterinary Tropical Diseases / unrestricted

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

A diverse assemblage of exquisitely-preserved fossil animals and plants were collected from Sawmill Sink blue hole in Abaco, Bahamas. More than 40 species have been identified including extinct tortoise, an extant crocodile, and birds that no longer live in The Bahamas. This study addresses the mechanisms that preserve fossils in blue holes and discusses paleoecological implications from faunal diversity and sediment composition. Blue holes are waterilled caves with surface openings that may trap animals and surface-driven vegetation. In Sawmill Sink the talus cone within the halocline acts as a substrate on which organics collect that drive microbe ecology. Their byproducts, hydrogen sulfide and anoxia, inhibit biological destruction and delay necrolysis. Low tidal flow and quiescent water conditions further enhance stability of the depositional environment. In addition, subaerial conditions during glacial lowstands allowed owls to roost; their deposits formed a rich assemblage of small fossil vertebrates.

M.Sc. (Geology) / Please refer to full text to view abstract

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.

No description available.

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