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Mauger L.A.,Southern Utah University | Velez E.,Kelonia Conservation Society | Cherkiss M.S.,Wetland and Aquatic Research Center | Brien M.L.,Wildlife Management International Pty. Ltd | And 2 more authors.
Nature Conservation | Year: 2017

Maintaining genetic diversity is crucial for the survival and management of threatened and endangered species. In this study, we analyzed genetic diversity and population genetic structure at neutral loci in American crocodiles, Crocodylus acutus, from several areas (Parque Nacional Marino Las Baulas, Parque Nacional Santa Rosa, Parque Nacional Palo Verde, Rio Tarcoles, and Osa Conservation Area) in Pacific Costa Rica. We genotyped 184 individuals at nine microsatellite loci to describe the genetic diversity and conservation genetics between and among populations. No population was at Hardy-Weinberg Equilibrium (HWE) over all loci tested and a small to moderate amount of inbreeding was present. Populations along the Pacific coast had an average heterozygosity of 0.572 across all loci. All populations were significantly differentiated from each other with both FST and RST measures of population differentiation with a greater degree of molecular variance (81%) found within populations. Our results suggest C. acutus populations in Pacific Costa Rica were not panmictic with moderate levels of genetic diversity. An effective management plan that maintains the connectivity between clusters is critical to the success of C. acutus in Pacific Costa Rica.


Manolis C.,Wildlife Management International Pty. Ltd | Zuur A.,Highland Statistics Ltd
PLoS ONE | Year: 2015

Conflicts between humans and crocodilians are a widespread conservation challenge and the number of crocodile attacks is increasing worldwide. We identified the factors that most effectively decide whether a victim is injured or killed in a crocodile attack by fitting generalized linear models to a 42-year dataset of 87 attacks (27 fatal and 60 non-fatal) by saltwater crocodiles (Crocodylus porosus) in Australia. The models showed that the most influential factors were the difference in body mass between crocodile and victim, and the position of victim in relation to the water at the time of an attack. In-water position (for diving, swimming, and wading) had a higher risk than on-water (boating) or on-land (fishing, and hunting near the water's edge) positions. In the in-water position a 75 kg person would have a relatively high probability of survival (0.81) if attacked by a 300 cm crocodile, but the probability becomes much lower (0.17) with a 400 cm crocodile. If attacked by a crocodile larger than 450 cm, the survival probability would be extremely low (<0.05) regardless of the victim's size. These results indicate that the main cause of death during a crocodile attack is drowning and larger crocodiles can drag a victim more easily into deeper water. A higher risk associated with a larger crocodile in relation to victim's size is highlighted by children's vulnerability to fatal attacks. Since the first recently recorded fatal attack involving a child in 2006, six out of nine fatal attacks (66.7%) involved children, and the average body size of crocodiles responsible for these fatal attacks was considerably smaller (384 cm, 223 kg) than that of crocodiles that killed adults (450 cm, 324 kg) during the same period (2006-2014). These results suggest that culling programs targeting larger crocodiles may not be an effective management option to improve safety for children. © 2015 Fukuda et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.


Tingley R.,University of Melbourne | Crase B.,National University of Singapore | Webb G.,Wildlife Management International Pty. Ltd | Webb G.,Charles Darwin University
Animal Conservation | Year: 2016

Invasive 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 (0.6-1.2m) 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. © 2015 The Zoological Society of London.


Manolis C.,Wildlife Management International Pty. Ltd | Appel K.,Parks and Wildlife Commission of the Northern Territory
Journal of Wildlife Management | Year: 2014

We reviewed the historical records of attacks by saltwater crocodiles (Crocodylus porosus) and the removal of problem saltwater crocodiles in the Northern Territory of Australia. Between 1977 and 2013, 5,792 problem crocodiles were removed, of which 69.04% were males and 83.01% were caught within the Darwin Crocodile Management Zone where suitable breeding habitats were hardly available. The most common size class was 150-200 cm and their mean size did not change significantly over years. This reflected the greater mobility of juvenile males as the majority of problem crocodiles, dispersing from core habitats that were occupied by dominant individuals. Eighteen fatal attacks and 45 non-fatal attacks occurred between 1971 and 2013. The rate of crocodile attacks, particularly non-fatal cases, increased over time. This increase was strongly related to the increasing populations of both humans and crocodiles, and the increasing proportion of larger (>180 cm) crocodiles. The management of human-crocodile conflict (HCC) should incorporate both human (e.g., public education and safety awareness) and crocodile (e.g., population monitoring, removal of problem crocodiles) components. Crocodiles in the 300-350-cm class were most responsible for attacks, and they should be strategically targeted as the most likely perpetrator. Approximately 60% of attacks occurred around population centers including remote communities. Problem crocodile capture and attacks both peak in the beginning (Sep-Dec) and end (Mar-Apr) of the wet season. However, fatal attacks occurred almost all year around. Attacks by crocodiles >400 cm often resulted in death of the victim (73.33%). Local and male victims were much more common than visitors and females, respectively. The most common activity of victims was swimming and wading. Despite the increasing rate of attacks over time, the Northern Territory's management program, and in particular the removal of problem crocodiles from urban areas, is considered to have reduced potential HCC. Public education about crocodile awareness and risks must be maintained. © 2014 The Wildlife Society. © The Wildlife Society, 2014.


PubMed | California State University, Fullerton, Environmental Research Institute of the Supervising Scientist, Charles Darwin University, Wildlife Management International Pty. Ltd and 3 more.
Type: Journal Article | Journal: Integrative and comparative biology | Year: 2015

Much of what is known about crocodilian nutrition and growth has come from animals propagated in captivity, but captive animals from the families Crocodilidae and Alligatoridae respond differently to similar diets. Since there are few comparative studies of crocodilian digestive physiology to help explain these differences, we investigated young Alligator mississippiensis and Crocodylus porosus in terms of (1) gross and microscopic morphology of the intestine, (2) activity of the membrane-bound digestive enzymes aminopeptidase-N, maltase, and sucrase, and (3) nutrient absorption by carrier-mediated and paracellular pathways. We also measured gut morphology of animals over a larger range of body sizes. The two species showed different allometry of length and mass of the gut, with A. mississippiensis having a steeper increase in intestinal mass with body size, and C. porosus having a steeper increase in intestinal length with body size. Both species showed similar patterns of magnification of the intestinal surface area, with decreasing magnification from the proximal to distal ends of the intestine. Although A. mississippiensis had significantly greater surface-area magnification overall, a compensating significant difference in gut length between species meant that total surface area of the intestine was not significantly different from that of C. porosus. The species differed in enzyme activities, with A. mississippiensis having significantly greater ability to digest carbohydrates relative to protein than did C. porosus. These differences in enzyme activity may help explain the differences in performance between the crocodilian families when on artificial diets. Both A. mississippiensis and C. porosus showed high absorption of 3-O methyl d-glucose (absorbed via both carrier-mediated and paracellular transport), as expected. Both species also showed surprisingly high levels of l-glucose-uptake (absorbed paracellularly), with fractional absorptions as high as those previously seen only in small birds and bats. Analyses of absorption rates suggested a relatively high proportional contribution of paracellular (i.e., non-mediated) uptake to total uptake of nutrients in both species. Because we measured juveniles, and most paracellular studies to date have been on adults, it is unclear whether high paracellular absorption is generally high within crocodilians or whether these high values are specific to juveniles.


Brien M.L.,Charles Darwin University | Brien M.L.,Wildlife Management International Pty. Ltd | Lang J.W.,University of Minnesota | Webb G.J.,Charles Darwin University | And 3 more authors.
PLoS ONE | Year: 2013

We examined agonistic behaviour in seven species of hatchling and juvenile crocodilians held in small groups (N = 4) under similar laboratory conditions. Agonistic interactions occurred in all seven species, typically involved two individuals, were short in duration (5-15 seconds), and occurred between 1600-2200 h in open water. The nature and extent of agonistic interactions, the behaviours displayed, and the level of conspecific tolerance varied among species. Discrete postures, non-contact and contact movements are described. Three of these were species-specific: push downs by C. johnstoni; inflated tail sweeping by C. novaeguineae ; and, side head striking combined with tail wagging by C. porosus . The two long-snouted species (C. johnstoni and G. gangeticus) avoided contact involving the head and often raised the head up out of the way during agonistic interactions. Several behaviours not associated with aggression are also described, including snout rubbing, raising the head up high while at rest, and the use of vocalizations. The two most aggressive species (C. porosus, C. novaeguineae) appeared to form dominance hierarchies, whereas the less aggressive species did not. Interspecific differences in agonistic behaviour may reflect evolutionary divergence associated with morphology, ecology, general life history and responses to interspecific conflict in areas where multiple species have co-existed. Understanding species-specific traits in agonistic behaviour and social tolerance has implications for the controlled raising of different species of hatchlings for conservation, management or production purposes. © 2013 Brien et al.


Brien M.L.,Charles Darwin University | Brien M.L.,Wildlife Management International Pty. Ltd | Webb G.J.,Charles Darwin University | Webb G.J.,Wildlife Management International Pty. Ltd | And 3 more authors.
Behaviour | Year: 2013

Detailed observations on groups of captive saltwater crocodile (Crocodylus porosus) hatchlings revealed sporadic periods of intense agonistic interactions, with 16 highly distinctive behaviours, in the morning (06:00 08:00Ah) and evening (17:00 20:00h) in shallow water. Ontogenetic changes in agonistic behaviour were quantified by examining 18 different groups of hatchlings, six groups each at 1 week, 13 weeks and 40 weeks after hatching. Agonistic interactions between hatchlings at 1 week of age (mean 7.3± 0.65/night) were not well-defined and varied in intensity (low, medium, high), number of individuals that were aggressive, and the outcome, while most interactions involved contact (94.5%). There were also clutch specific differences in the frequency of agonistic interactions. At 13 and 40 weeks, a more hierarchal dominance relationship appeared to be established which primarily involved aggression submission interactions. Agonistic interactions were more frequent (13 weeks 9.7 ± 0.61/night; 40 weeks 22.2± 0.61/night) and intense (medium, high), but shorter in duration, in which the subordinate individual fled in response to an approach by a dominant animal that often gave chase but did not make contact. While the full repertoire of behaviour was displayed by hatchlings at 1 week of age, a smaller subset based on dominance status was displayed among 13- and 40-week-old hatchlings. Agonistic behaviour occurs in C. porosus shortly after hatching and is important in establishing and maintaining dominance hierarchies that are characterised by aggression submission interactions. This type of interaction appears typical for C. porosus both in the wild and in captivity, and may be important in preventing serious injury in a species equipped with formidable armoury. Dispersal by hatchling C. porosus at around 13 weeks of age appears to be driven by a growing intolerance of conspecifics, while territoriality is apparent at an early age. Consequently, agonistic behaviour and social status may be major contributors to the observed differences in growth rates and survival in captivity. © Koninklijke Brill NV, Leiden, The Netherlands.


Brien M.L.,Charles Darwin University | Brien M.L.,Wildlife Management International Pty Ltd | Webb G.J.,Charles Darwin University | Webb G.J.,Wildlife Management International Pty Ltd | And 2 more authors.
Australian Journal of Zoology | Year: 2013

We examined agonistic behaviour in hatchling Australian freshwater crocodiles (Crocodylus johnstoni) at 2 weeks, 13 weeks, and 50 weeks after hatching, and between C. johnstoni and saltwater crocodiles (Crocodylus porosus) at 40-50 weeks of age. Among C. johnstoni, agonistic interactions (15-23s duration) were well established by two weeks old and typically involved two and occasionally three individuals, mostly between 17:00 and 24:00hours in open-water areas of enclosures. A range of discrete postures, non-contact and contact movements are described. The head is rarely targeted in contact movements with C. johnstoni because they exhibit a unique 'head raised high' posture, and engage in 'push downs'. In contrast with C. porosus of a similar age, agonistic interactions between C. johnstoni were conducted with relatively low intensity and showed limited ontogenetic change; there was also no evidence of a dominance hierarchy among hatchlings by 50 weeks of age, when the frequency of agonistic interactions was lowest. Agonistic interactions between C. johnstoni and C. porosus at 40-50 weeks of age were mostly low level, with no real exclusion or dominance observed. However, smaller individuals of both species moved slowly out of the way when a larger individual of either species approached. When medium- or high-level interspecific interactions did occur, it was between similar-sized individuals, and each displayed species-specific behaviours that appeared difficult for contestants to interpret: there was no clear winner or loser. The nature of agonistic interactions between the two species suggests that dominance may be governed more strongly by size rather than by species-specific aggressiveness. © CSIRO 2013.


Somaweera R.,University of Sydney | Brien M.,Wildlife Management International Pty. Ltd | Brien M.,Charles Darwin University | Shine R.,University of Sydney
Herpetological Monographs | Year: 2013

Although adult crocodilians have few predators (mostly humans and other crocodilians), hatchlings and eggs are killed and consumed by a diverse array of invertebrates, fishes, anurans, reptiles, birds, and mammals. We review published literature to evaluate the incidence of predation in crocodilian populations, and the implications of that mortality for crocodilian life-history evolution. Presumably because predation is size-dependent, small-bodied crocodilian taxa appear to be more vulnerable to predation (across a range of life stages) than are larger-bodied species. Several features of crocodilian biology likely reflect adaptations to reducing vulnerability to predation. For example, the threat of predation may have influenced the evolution of traits such as nest-site selection, maternal care of eggs and hatchlings, crèche behavior in hatchlings, and cryptic coloration and patterning. Even for such large and superficially invulnerable taxa such as crocodilians, the avoidance of predation appears to have been a significant selective force on behavior, morphology, and ecology. © 2013 The Herpetologists' League, Inc.


Brien M.L.,Charles Darwin University | Brien M.L.,Wildlife Management International Pty. Ltd | Webb G.J.,Charles Darwin University | Webb G.J.,Wildlife Management International Pty. Ltd | And 2 more authors.
PLoS ONE | Year: 2014

Hatchling fitness in crocodilians is affected by "runtism" or failure to thrive syndrome (FTT) in captivity. In this study, 300 hatchling C. porosus, artificially incubated at 32°C for most of their embryonic development, were raised in semi-controlled conditions, with growth criteria derived for the early detection of FTT (within 24 days). Body mass, four days after hatching (BM4d), was correlated with egg size and was highly clutch specific, while snout-vent length (SVL4d) was much more variable within and between clutches. For the majority of hatchlings growth trajectories within the first 24 days continued to 90 days and could be used to predict FTT affliction up to 300 days, highlighting the importance of early growth. Growth and survival of hatchling C. porosus in captivity was not influenced by initial size (BM4d), with a slight tendency for smaller hatchlings to grow faster in the immediate post-hatching period. Strong clutch effects (12 clutches) on affliction with FTT were apparent, but could not be explained by measured clutch variables or other factors. Among individuals not afflicted by FTT (N = 245), mean growth was highly clutch specific, and the variation could be explained by an interaction between clutch and season. FTT affliction was 2.5 times higher among clutches (N = 7) that hatched later in the year when mean minimum air temperatures were lower, compared with those clutches (N = 5) that hatched early in the year. The results of this study highlight the importance of early growth in hatchling C. porosus, which has implications for the captive management of this species. © 2014 Brien et al.

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