Estuarine crocodile (Crocodylus porosus)
IUCN Red List Status – Least Concern ver 3.1
Project coordinator: Sai Kerisha Kntayya
Title: Assessing the impacts of habitat fragmentation and subsequent anthropogenic expansion on the behavioural, population, and nesting ecology of the estuarine crocodile, Crocodylus porosus.
Status – Completed
Project coordinator: Dr Luke Evans
Laboratory assistant: Anita B. Tahir
The project sought to examine the effects of habitat loss and fragmentation on the ecology and population genetics of the estuarine crocodile (C. porosus). Additionally, the role played by humans in this anthropogenically-altered landscape was examined. The project utilised a host of technologies, some previously established, some completely novel in crocodilian research, in order to provide a new insight into how the landscape is utilised by these cryptic predators. This project represents a first detailed look at Sabah’s crocodilian population, as well as being the first active crocodile research carried out in Sabah’s longest river. A major aim of the project was to establish base-line behavioural ecology data in equatorial rainforest ecotypes, whilst also examining how prior population fluctuations have impacted the genetic health of the regions crocodiles. One major output from the project will be an understanding of how to move forward with a future management plan for Sabah’s crocodiles, in order to mitigate future conflict whilst maintaining active and healthy wild populations.
Three major technological methodologies were employed during the project, namely satellite tracking, drone reconnaissance, and microsatellite and mitochondrial analysis.
Implementation of three distinct satellite tracking technologies, that included Iridium, ARGOS, and remote download systems. Tags were all attached at the nuchal plate, in accordance with the method set forth by Kay (2004). Tags were attached to both male and female crocodiles, ranging from 2.12 m up to 5.18 m.
Drone technology was utilised for the first time in crocodilian research. This aerial photography utilising programmable autopilot technology allowed for the selective surveying of potential nesting habitats. Using a ‘fixed wing’ aircraft enabled single flights of in excess of 35 km. This level of aerial coverage provides a repeatable method of nest surveying. The results from confirmed nest sites allowed further refinement of modelled flight areas ensuring that a high proportion of detection could be ensured with the minimum of flight time. For further details regarding methodology please see Evans et al. (2015).
Microsatellite and mtDNA
Both microsatellite and mtDNA analysis are established methodologies utilised to provide an understanding of a range of demographic traits. The project sought to utilise these analyses to gain an understanding of genetic health of the population, as well as to understand whether or not recent a population bottleneck had resulted in decrease in observable heterozygosity. In order to do this, a locus from the control region of the mitochondrial genome was sequenced for 122 individuals captured from the Kinabatangan. Additionally, 24 microsatellite loci were selected from previously published works.
A total of nine individuals were tagged, with seven of those units providing usable data. Males were found to adhere to one of two behavioural strategies, territorial and nomadic, mirroring findings of Campbell et al. (2013). Territory sizes were, however, found to be smaller than those described in Australia, this was attributed to increased prey availability and ecosystem productivity. Only two females were tagged and appeared to also displaying differences in behavioural strategy. However, due to the small sample size further work is required to confirm this.
Nests were detectable aerially through the use of drones and medium-large scale surveys shown to be feasible. Nests were found to all display a number of similarities in terms of habitat characteristics allowing for refined modelling of survey locations. This provides an
- Stepping stone to tangible management plan.
- Placing of warning signs in areas deemed to be at high risk of human-crocodile conflict.
Collaborators: Wildlife Rescue Unit, Sabah Wildlife Department – Local counterpart – Silverster Saimin.
Title: Landscape Genetics and Habitat Viability of the Estuarine Crocodile in Sabah.
PhD Candidate: Sai Kerisha Kntayya
Supervisors: Benoit Goossens, Pablo Orozco Ter-Wengel
Institution: Cardiff University
Duration: October 2017 – October 2022
- To estimate baseline population demographic information of the estuarine crocodile in Sabah using common crocodilian census techniques.
- To characterize the spatial ecology of the estuarine crocodile population in Sabah by satellite tracking individuals to determine movement patterns, home range and habitat use.
- To characterize the genetic diversity of the estuarine crocodile populations in Sabah using genetic markers.
- To determine the influence of landscape structure on the gene flow of estuarine crocodile populations, in Sabah.
- To determine extinction vulnerabilities and future population trends of the estuarine crocodile in Sabah using Population Viability Analysis (PVA).
A total of 10 rivers, comprising six districts in Sabah will be surveyed, covering all regions and major river systems in the state that are known to harbor crocodile populations. Historic data from these previous surveys will facilitate population trends identification. Visual encounter surveys will be carried out by boat. Each stretch of river will be surveyed upstream from a motorboat at night for approximately 50km depending on the river. A H14.2 led lenser head torch will be used to identify the red eye shine of crocodiles. Once an individual is spotted, the boat is brought as close as possible to the animal. Once in close proximity to the animal, a GPS location, the habitat category and an estimated size of the animal will be recorded into a data sheet. Other parameters such as density, distance surveyed and river systems will also be recorded. Multiple surveys will be conducted across the rivers, each during the same time of previous years to avoid seasonal bias. Individuals of not more than 70cm in length will be sampled by hand capture. Once secure, a number of morphological parameters will be recorded including total length, snout-vent length, and head length. Weight will be recorded by a spring-balanced weight. Tagging of adult crocodiles for spatial analysis will take place using iridium satellite tags from African Wildlife Tracking (AWT) company providing location fixes and allowing for two-way data communication. During the process of tagging, monomorphic measurements will be taken and a tissue sample will be obtained for genetic analysis.
Expected outcomes, how is this research going to impact the species/habitat
Whilst estuarine crocodile populations in Sabah have recovered following state-wide protection, there have been no studies on the extinction risk of this animal in the context of the rigorous state economic development that will undoubtedly cause future alterations to the landscape. This study is vital due to the recent and escalating occurrences of HCC throughout Sabah, prompting current interest by the state government of Sabah to evaluate the ramifications of a legal harvest. The results of this study will help to reveal whether non-detriment findings (NDF) on the estuarine crocodile population in Sabah can be demonstrated, and consequently provide management plans to establish whether, and subsequently ensure, sustainable utilization and ultimately, the survival of this species.