Saltwater Crocodile Crocodylus Porosus Research Articles

Wildlife conservation through traditional values: alarming numbers of crocodile attacks reported from Timor-Leste

AbstractOn the IUCN Red List the saltwater crocodile Crocodylus porosus is categorized globally as Least Concern, with national populations ranging from fully recovered to extinct. The saltwater crocodile population of the Southeast Asian island nation of Timor-Leste was severely depleted by colonial hunting but has recovered since independence in 2002. During 2007–2014 there was a 23-fold increase in reported crocodile attacks (104 documented attacks), concomitant with a 2% annual increase in the human population. Public tolerance to attacks and the reluctance to harm crocodiles are entwined with reverence of crocodiles as sacred beings by most but not all Timorese people. In 2022, 7–8 years after our previous assessment, we visited five sites on the south coast of Timor-Leste in Lautém, Viqueque, Manufahí and Cova Lima municipalities. High rates of crocodile attacks continue. We obtained 35 records of attacks for 2015–2022 (34% fatal). In the municipalities where crocodile attacks occurred (Lautém, Viqueque, Cova Lima), the sacred status of crocodiles prevented inhabitants from harming them in retribution. In Manufahí, where no attacks were reported, such traditional values never existed and crocodiles were hunted for subsistence and to improve safety. The design of a context-specific crocodile management programme that respects the reverence attributed to crocodiles by most people but reduces the risk of people being attacked by crocodiles is a conservation management challenge for the government of Timor-Leste. The developing tourism industry, which relies on coastal beaches and reefs, is jeopardized by the risk of crocodile attacks.

Human–crocodile interactions in the western Solomon Islands: the importance of local data for reducing attacks on people

AbstractInteractions between people and the saltwater crocodile Crocodylus porosus frequently occur on islands and in coastal regions. Saltwater crocodiles impact people's lives and livelihoods by attacking them, resulting in minor or serious injuries, and by interfering in people's foraging activities. Retaliation may include killing the crocodiles involved. To reduce such human–crocodile interactions, data about the occurrence of incidents are required. We present data on encounters with crocodiles and attacks on people in the Roviana Lagoon, Solomon Islands. Data includes time of incident, gender, age and activity of the victim, water conditions and what happened to the crocodile after the incident. We used a questionnaire to capture the details of incidents that occurred during 2000–2020 in the villages of Dunde, Baraulu, Nusa Hope and Kozou. Most incidents were in the evening, mostly involving women, and most victims were aged 20–39 years or ≥ 60 years. In all cases people were attacked while gleaning for shellfish in the mangroves. Attacks occurred irrespective of whether the water was clear or murky, and in all cases the crocodiles were not killed. Such site-specific data will facilitate the formulation of strategies for reducing negative interactions between people and crocodiles in this particular location. Although the saltwater crocodile is categorized as Least Concern on the IUCN Red List, research such as this provides data that can be used for promoting coexistence with and conservation of this species.

Lost to the Sea: Predicted Climate Change Threats to Saltwater Crocodile Nesting Habitat

Climate change is predicted to have devastating impacts on apex predators such as eliminating their required habitats. Crocodilians are no exception as most species require freshwater for nesting, and such freshwater habitats are particularly vulnerable to saltwater inundation (SWI) caused by the sea level rise (SLR) from global warming. Here, we examined the impacts of climate change on saltwater crocodiles Crocodylus porosus in terms of the potential loss of nesting habitat in the Northern Territory, Australia; an area that contains the world’s most extensive nesting habitat for the species. Our spatial model, derived from 730 nest locations and selected environmental features, estimated a total of 32,306.91 km2 of current suitable habitat across the study region. The most important variable was distance to perennial lakes (71.0% contribution, 87.5% permutation importance), which is negatively correlated with nesting habitat suitability. We found that projected changes in temperature and rainfall by 2100 could impact the area of suitable nesting habitat negatively or positively (0.33% decrease under low future emission climate scenario, and 32.30% increase under high emission scenario). Nevertheless, this can be canceled by the strong negative impact of SLR and concomitant SWI on nesting areas. A portion (16.40%) of the modeled suitable habitat for a subsection of our study area, the Kakadu Region, were already subject to > 0.25 m SWI in 2013. The suitable area for nesting in this region is predicted to be further reduced to 1775.70 km2 with 1.1 m SLR predicted for 2100, representing 49.81% loss between 2013 and 2100. Although the estimates of habitat loss do not account for the potential creation of new habitat, nor for the uncertainty in the degree of future SLR, our results suggest that SLR driven by continuing global warming can be the major threat to mound-nest-building crocodilians including C. porosus, rather than direct impacts from changes in temperature and rainfall. The degree of impact on saltwater crocodiles will be determined by the interplay between the loss of nesting habitat, which would appear inevitable under current global warming, and the ability to expand into new areas created by the expansion of the tropics.

New Recorded of Saltwater Crocodile Crocodylus porosus Schneider, 1801 from East Coast Mangrove Ecosystem in Surabaya, East Jawa, Indonesia

A single specimen of saltwater crocodile Crocodylus porosus Schneider, 1801 (1.50 cm in length) was captured and photographed by a local fisherman by gill net at fishpond around mangrove ecosystem of east coast Surabaya on December 2020. The location where the estuarine crocodile caught is an important wetland area in Surabaya with an excellent mangrove cover. Wonorejo mangrove location is about 10 km from the centre of Surabaya, the second-largest city in Indonesia. This finding is considered as a first reported of C. porosus in Surabaya, and at the same time is proof of the importance of the mangrove area on the east coast of Surabaya as a habitat for wildlife that must be conserved appropriately. Routine monitoring of mangrove areas, including their wildlife, is essential so that they are not displaced by the development of the city which changes the land function to become a residential area.

Post-testicular sperm maturation in the saltwater crocodile Crocodylus porosus: assessing the temporal acquisition of sperm motility.

Conservation efforts to secure the long-term survival of crocodilian species would benefit from the establishment of a frozen sperm bank in concert with artificial breeding technologies to maintain genetic diversity among captive assurance populations. Working towards this goal, our research has focused on the saltwater crocodile Crocodylus porosus as a tractable model for understanding crocodilian sperm physiology. In extending our systematic characterisation of saltwater crocodile spermatozoa, in this study we examined the development of motility during sperm transport through the excurrent duct system of the male crocodile. The results show that approximately 20% of crocodile testicular spermatozoa are immediately motile but experience a gradient of increasing motility (percentage motile and rate of movement) as they transit the male reproductive tract (epididymis). Moreover, we confirmed that, as in ejaculated crocodile spermatozoa, increased intracellular cAMP levels promoted a significant and sustained enhancement of sperm motility regardless of whether the cells were isolated from the testis or epididymis. Along with the development of artificial reproductive technologies, this research paves the way for the opportunistic recovery, storage and potential utilisation of post-mortem spermatozoa from genetically valuable animals.

Plasma and acrosomal membrane lipid content of saltwater crocodile spermatozoa.

This study describes the chemical lipid composition of the sperm plasma and acrosomal membranes of the saltwater crocodile Crocodylus porosus with the aim of providing new insights into sperm physiology, particularly that associated with their preservation ex vivo . The specific fatty acid composition of the sperm plasma and acrosomal membranes is documented. The mean (±s.d.) ratio of unsaturated to saturated membrane fatty acids within the plasma membrane was 2.57±0.50, and was determined to be higher than a similar analysis of the lipids found in the acrosomal membrane (0.70±0.10). The saltwater crocodile sperm plasma membrane also contained remarkably high levels of cholesterol (mean (±s.d.) 40.7±4.5 nmol per 106 sperm cells) compared with the spermatozoa of other amniote species that have so far been documented. We suggest that this high cholesterol content could be conferring stability to the crocodile sperm membrane, allowing it to tolerate extreme osmotic fluxes and rapid changes in temperature. Our descriptive analysis now provides those interested in reptile and comparative sperm physiology an improved baseline database for interpreting biochemical changes associated with preservation pathology (e.g. cold shock and cryoinjury), epididymal sperm maturation and capacitation/acrosome reaction.

Integrating local perspectives into conservation could facilitate human–crocodile coexistence in the Ayeyarwady Delta, Myanmar

AbstractConservation will always fail when it does not address the drivers of biodiversity loss, which in many cases involves understanding human behaviours and the attitudes that underlie them. The saltwater crocodile Crocodylus porosus is a keystone species in mangrove wetlands but also a dangerous predator that affects people's safety and livelihoods. Although saltwater crocodiles are protected under the Myanmar Biodiversity and Protected Area Law, the government has not integrated local people's attitudes into conservation and management. As a consequence, saltwater crocodiles, although categorized as Least Concern on the IUCN Red List, are restricted to a single protected area, Meinmahlakyun Wildlife Sanctuary, in Myanmar. To examine local attitudes towards the species, we investigated local knowledge about the environment, crocodiles, habitats and threats, awareness of human–crocodile conflict, and perceptions of the benefits and impacts of saltwater crocodile conservation through questionnaires in 244 households in 17 villages. We found that people were highly knowledgeable about the local environment, saltwater crocodiles, and their habitats. People with seasonal livelihoods that rely on natural resources from Meinmahlakyun had negative attitudes towards crocodile conservation. People were likely to have negative attitudes if they perceived there were no benefits from conserving the species. Law enforcement through restricting resource access does not enhance conservation success and builds resentment towards the conservation of the species. Local people suggested that, as a basis for management, understanding risks posed by crocodiles was the best approach to facilitate human–crocodile coexistence in the Ayeyarwady delta region.

Harvesting predators: simulation of population recovery and controlled harvest of saltwater crocodiles Crocodylus porosus

Abstract ContextThe population of saltwater crocodiles, Crocodylus porosus, in the Northern Territory, Australia, has been recovering from a period of intensive, unregulated harvest (1945–1971) since protection in 1971. Consequently, the management goal is shifting from restoring a seriously depleted population to managing an abundant population through controlled harvests for both commercial purposes and public safety. AimsWe conducted this study to (1) examine whether the controlled harvest of eggs and adults since protection has had an adverse effect on population size and structure, and (2) explore the effect of future harvest scenarios on population size and structure by adjusting harvest levels of both eggs and adults. MethodsOn the basis of 40 years of population monitoring data and knowledge of population attributes from previous research, we developed density-dependent, structured matrix population models to explore our aims. Key resultsThe models supported that the depleted population recovered rapidly under protection and that the harvest rates since protection were benign. The model estimated the 2017 harvested population, 46 years after protection, to be ~102000 non-hatchlings (>0.6m crocodiles), of which 42.2% are large (>2.1m total length) individuals. This is similar to the estimated population before the period of intensive, unregulated harvest. Like other crocodilians, the harvest simulations showed that the viability of the population is highly sensitive to adult survival rates. The estimated population should be able to sustain an annual harvest of up to 135500 eggs if the harvest of large crocodiles remains small (<500 per year). ConclusionsAlthough egg harvest has little impact on population size and structure, population size is sensitive to adult harvest. ImplicationsCrocodile populations are highly sensitive to adult survival, which needs to be taken into account when considering future harvest scenarios.

Estimating population status and site occupancy of saltwater crocodiles Crocodylus porosus in the Ayeyarwady delta, Myanmar: Inferences from spatial modeling techniques

Saltwater crocodiles Crocodylus porosus are listed as critically endangered in Myanmar because they are limited to Meinmahlakyun Wildlife Sanctuary (MKWS) in the Ayeyarwady delta region. Little contemporary data exists on their distribution and population size which hinders effective conservation and management. We conducted standardized spotlight surveys and camera trap surveys along the rivers inside MKWS, and two nearby reserved forests. We used Hierarchical N-mixture models, Spatial Count models, and the relative abundance index to estimate site use by and population sizes of saltwater crocodiles in the Ayeyarwady delta. To address biases in detectability, we used maximum-likelihood and Bayesian approaches (1) to assess occupancy (site use) and population parameters of saltwater crocodiles, and (2) to assay abiotic and anthropogenic factors affecting it. Saltwater crocodiles were more likely to be abundant and occupy in the waterways inside MKWS than the reserved forests, and in the narrow and low salinity waterways than the wide and high salinity ones. Abundance of saltwater crocodiles was lower in areas with the human settlements than in areas with no settlement. Creeks within MKWS had moderate salinity and no human settlement and therefore it can be regared as the last remaining optimal saltwater crocodile habitat of the Ayeyarwady Delta. We estimated the saltwater crocodile population sizes in MKWS were 75 ± 9.92 individuals as absolute spotlight index, 58 ± 8.02 individuals as the maximum likelihood estimate of the N-mixture models and 68 ± 10.00 individuals as the Bayesian estimate of the spatial count models. Current population estimates of saltwater crocodiles are lower than the previously reported population size in 1999, and the declining population is now restricted to MKWS. We suggest developing buffer zones in the reserved forests around the wildlife sanctuary to increase habitat areas for saltwater crocodiles and to improve the outlook for long-term saltwater crocodile survival in Myanmar.

Impacts of anthropogenic pressures on the contemporary biogeography of threatened crocodilians in Indonesia

AbstractThe Greater Sunda region of South-east Asia supports a rich diversity of economically and ecologically important species. However, human pressures are reshaping contemporary biogeography across the region. Megafaunal distributional patterns have been particularly affected because of deforestation, poaching and human–wildlife conflict. Crocodilians are at the centre of these conflicts in Indonesia and yet remain poorly studied across much of the archipelago. We conducted population surveys of salt-water crocodiles Crocodylus porosus and false gharials Tomistoma schlegelii in Sumatra, and examined whether crocodile abundance and distribution are correlated with variations in human disturbance, fishing pressure, and habitat type. We then used these data to model remaining suitable habitat for T. schlegelii across South-east Asia. We found that abundance of T. schlegelii and C. porosus was correlated with distance from human settlements, and fish-trapping pressure. We recorded the presence of T. schlegelii in a river system in which it was previously unknown, thus expanding the known range of the species. We also found that the predicted remaining suitable habitat for T. schlegelii in Indonesia is largely limited to areas of low human activity. From these empirical and modelling approaches we propose several key conservation priorities: (1) eliminate the use of fish traps in remaining patches of T. schlegelii habitat, (2) prioritize crocodile population surveys in remaining suitable habitat, particularly in remote areas, (3) consider T. schlegelii to be potentially Endangered locally in Sumatra, and (4) expand existing reserves around the Lower Kampar River and Berbak National Park/Sembilang National Park areas of Sumatra.

A new marker based on the avian spindlin gene that is able to sex most birds, including species problematic to sex with CHD markers.

We have developed a new marker (Z43B) that can be successfully used to identify the sex of most birds (69%), including species difficult or impossible to sex with other markers. We utilized the zebra finch Taeniopygia guttata EST microsatellite sequence (CK309496) which displays sequence homology to the 5' untranslated region (UTR) of the avian spindlin gene. This gene is known to be present on the Z and W chromosomes. To maximize cross-species utility, the primer set was designed from a consensus sequence created from homologs of CK309496 that were isolated from multiple distantly related species. Both the forward and reverse primer sequences were 100% identical to 14 avian species, including the Z chromosome of eight species and the chicken Gallus gallus W chromosome, as well as the saltwater crocodile Crocodylus porosus. The Z43B primer set was assessed by genotyping individuals of known sex belonging to 61 non-ratite species and a single ratite. The Z and W amplicons differed in size making it possible to distinguish between males (ZZ) and females (ZW) for the majority (69%) of non-ratite species tested, comprising 10 orders of birds. We predict that this marker will be useful for obtaining sex-typing data for ca 6,869 species of birds (69% of non-ratites but not galliforms). A wide range of species could be sex-typed including passerines, shorebirds, eagles, falcons, bee-eaters, cranes, shags, parrots, penguins, ducks, and a ratite species, the brown kiwi, Apteryx australis. Those species sexed include species impossible or problematic to sex-type with other markers (magpie, albatross, petrel, eagle, falcon, crane, and penguin species). Zoo Biol. 35:533-545, 2016. © 2016 The Authors. Zoo Biology published by Wiley Periodicals, Inc.

Long‐term monitoring reveals declines in an endemic predator following invasion by an exotic prey species

AbstractInvasive predators can cause population declines in native prey species, but empirical evidence linking declines of native predators to invasive prey is relatively rare. Here, we document declines in an Australian freshwater crocodile Crocodylus johnstoni population following invasion of a toxic prey species, the cane toad Rhinella marina. Thirty‐five years of standardized spotlight surveys of four segments of a large river in northern Australia revealed that the density of freshwater crocodiles decreased following toad invasion and continued to decline thereafter. Overall, intermediate‐sized freshwater crocodiles (0.6–1.2 m) were most severely impacted. Densities of saltwater crocodiles Crocodylus porosus increased over time and were generally less affected by toad arrival, although toad impacts were inconsistent across survey sections and size classes. Across the entire river, total freshwater crocodile densities declined by 69.5% between 1997 and 2013. Assessments of the status of this species within other large river systems in northern Australia, where baseline data are available from before the toads arrived, should be prioritized. Our findings highlight the importance of long‐term monitoring programmes for quantifying the impacts of novel and unforeseen threats.

Characterization of crocodile teeth: Correlation of composition, microstructure, and hardness

Structure and composition of teeth of the saltwater crocodile Crocodylus porosus were characterized by several high-resolution analytical techniques. X-ray diffraction in combination with elemental analysis and infrared spectroscopy showed that the mineral phase of the teeth is a carbonated calcium-deficient nanocrystalline hydroxyapatite in all three tooth-constituting tissues: Dentin, enamel, and cementum. The fluoride content in the three tissues is very low (<0.1 wt.%) and comparable to that in human teeth. The mineral content of dentin, enamel, and cementum as determined by thermogravimetry is 71.3, 80.5, and 66.8 wt.%, respectively. Synchrotron X-ray microtomography showed the internal structure and allowed to visualize the degree of mineralization in dentin, enamel, and cementum. Virtual sections through the tooth and scanning electron micrographs showed that the enamel layer is comparably thin (100-200 μm). The crystallites in the enamel are oriented perpendicularly to the tooth surface. At the dentin-enamel-junction, the packing density of crystallites decreases, and the crystallites do not display an ordered structure as in the enamel. The microhardness was 0.60±0.05 GPa for dentin, 3.15±0.15 GPa for enamel, 0.26±0.08 GPa for cementum close to the crown, and 0.31±0.04 GPa for cementum close to the root margin. This can be explained with the different degree of mineralization of the different tissue types and is comparable with human teeth.

Standardised method of spotlight surveys for crocodiles in the Tidal Rivers of the Northern Territory, Australia

Standardised spotlight survey procedures have been an integral part of long-term (1975-2012) monitoring programs for Saltwater Crocodiles Crocodylus porosus and Freshwater Crocodiles C. johnstoni in tidal rivers of the Northern Territory (NT) of Australia. These programs, implemented four years after depleted Saltwater Crocodile populations were protected from hunting in 1971, have been instrumental in documenting post-protection population recovery and evaluating management interventions. This article describes a standardised method for spotlight survey of crocodiles in tidal rivers, with particular emphasis on practical aspects that were not previously documented. It also shows example survey data and how it is analysed. This practical guide is primarily oriented at maintaining survey standardisation within the NT, but it should help wildlife managers to use standardised spotlight counting as a monitoring tool for crocodilian species in similar habitats elsewhere.

Providencia rettgeri-associated Septicemia and Meningoencephalitis in Juvenile Farmed American AlligatorsAlligator mississippiensis

Abstract Providencia rettgeri was found to be associated with high mortalities in farmed American alligators Alligator mississippiensis being grown under intensive culture conditions on a commercial aquaculture facility. The outbreak was likely precipitated by an episode of severe temperature stress resulting from a thermostat that was improperly set. Animals were lethargic and in poor physical condition, and exhibited neurologic signs, including head tilt and circling. Histopathology findings revealed heterophilic meningoencephalitis, pneumonia, hepatitis, and splenitis. The epizootic was successfully resolved by adding neomycin sulfate to the diet. Providencia rettgeri is recognized as an infrequent opportunistic pathogen of captive American alligators and the saltwater crocodile Crocodylus porosus in Australia. Meningoencephalitis in alligators has not previously been attributed to P. rettgeri.

Conservation and sustainable use of wildlife - an evolving concept

The proposition that wildlife conservation can sometimes be enhanced through allowing and even promoting the harvesting of wildlife is a sensitive issue. For the last 30 years, conservation has tended to focus on protecting rather than using wildlife. Yet conservation through sustainable use (CSU) is now a mainstream conservation strategy, and research on sustaining rather than stopping uses is commonplace. This paper discusses some of the fundamental and confusing elements of the CSU concept. Two case histories are discussed: Saltwater Crocodiles Crocodylus porosus in the Northern Territory of Australia, and Hawksbill Turtles Eretmochelys imbricata in Cuba. That wildlife populations are themselves highly dynamic entities, capable of adapting to harvest reductions, is well established, but often not appreciated. To advance conservation, research at the dynamic population level of resolution needs to take precedence over research on individual population dynamics.

Relationships between blood pressure and heart rate in the saltwater crocodile Crocodylus porosus.

The cardiac limb of the baroreflex loop was studied in the saltwater crocodile Crocodylus porosus. The classical pharmacological methodology using phenylephrine and sodium nitroprusside was used to trigger blood pressure changes, and the resulting alterations in heart rate were analysed quantitatively using a logistic function. Interindividual differences in resting heart rates and blood pressures were observed, but all seven animals displayed clear baroreflex responses. Atropine and sotalol greatly attenuated the response. A maximal baroreflex gain of 7.2 beats min-1 kPa-1 was found at a mean aortic pressure of 6.1 kPa, indicating the active role of the baroreflex in a wide pressure range encompassing hypotensive and hypertensive states. At the lowest mean aortic pressures (5.0 kPa), the synergistic role of the pulmonary-to-systemic shunt in buffering the blood pressure drop also contributes to blood pressure regulation. Pulse pressure showed a better correlation with heart rate and also a higher gain than mean aortic, systolic or diastolic pressures, and this is taken as an indicator of the existence of a differential control element working simultaneously with a linear proportional element.

Renivermis crocodyli (Digenea: Exotidendriidae) n. g., n. sp. from the kidneys of the saltwater crocodileCrocodylus porosus in Australia

Renivermis crocodyli, n. g., n. sp., is described from the kidneys of the saltwater crocodileCrocodylus porosus Schneider from northern Australia. The genusRenivermis is grouped withExotidendrium Mehra, 1935 andSimhatrema Chattopadhyaya, 1970 in the family Exotidendriidae Mehra, 1935. An amended diagnosis of the family and a key to its genera are given.

Energy Metabolism during Unrestrained Submergence in the Saltwater Crocodile Crocodylus porosus

Metabolic rate and the relative contributions of aerobiosis and anaerobiosis to energy supply during unrestrained submergence were calculated in juvenile Crocodylus porosus. Voluntary undisturbed dives were short in duration (mean = 4.7 min ± 0.3 SEM; n = 60) and did not result in a decline in metabolic rate below predive levels. These dives were aerobic because negligible quantities of blood lactate were generated. Crocodiles surfaced before pulmonary O₂ tensions (PLo2) dropped below 70 mmHg (mean = 75 mmHg ± 4.4 SEM; n = 23), and it is proposed that metabolic rate does not decline during voluntary dives because tissues do not become hypoxic. When submergence was prolonged beyond voluntary limits, aerobic metabolism (estimated from the rate of decline in PLo2) did not decline until PLo2 fell below 50 mmHg. This suggests that internal O₂ tensions rather than submergence per se influenced aerobic metabolism during these dives. Crocodiles appear to change aerobic metabolism during submergence to meet specif...

Saltwater crocodile attacks on man

All instances of attacks on humans by large saltwater crocodiles Crocodylus porosus over a ten-year period are reported. Despite daily human intrusions into the crocodile's aquatic environment and the presence of extremely large male crocodiles (the usual offenders), only four instances of attack occurred in 10 years. Hence, saltwater crocodiles in Orissa, India, cannot be considered a serious threat to human life and actively avoid preying on man—an easy victim.