Landscape genetics and habitat viability of the estuarine crocodile in Sabah

PhD Researcher: Sai Kerisha Kntayya

Supervisors: Benoit Goossens, Pablo Orozco Ter-Wengel

Institution: Cardiff University

Duration: October 2017 – October 2022

Research questions

1. To estimate baseline population demographic information of the estuarine crocodile in Sabah using common crocodilian census techniques.
2. To characterise the spatial ecology of the estuarine crocodile population in Sabah by satellite tracking individuals to determine movement patterns, home range and habitat use.
3. To characterise the genetic diversity of the estuarine crocodile populations in Sabah using genetic markers.
4. To determine the influence of landscape structure on the gene flow of estuarine crocodile populations in Sabah.
5. To determine extinction vulnerabilities and future population trends of the estuarine crocodile in Sabah using Population Viability Analysis (PVA).

Methods

A total of 10 rivers, comprising six districts in Sabah, were surveyed, covering all regions and major river systems in the state that are known to harbour crocodile populations. Historical data from these previous surveys were used to facilitate population trend identification. Visual encounter surveys were carried out by boat. Each stretch of river was surveyed upstream from a motorboat at night for approximately 50km, depending on the river. An H14.2 led lenser head torch was used to identify the red eye shine of crocodiles. Once an individual was spotted, the GPS location, habitat category and the estimated size of the animal were recorded into a data sheet.

Multiple surveys were conducted, each at the same time as surveys, to avoid seasonal bias. Individuals of not more than 70cm in length were sampled by hand capture. Once secured, a number of morphological parameters were recorded, including total length and weight. Tagging of adult crocodiles for spatial analysis was used 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 were taken, including tissue samples for genetic analysis.

Expected outcomes: how will this research 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 was undertaken 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 helped inform the State whether non-detriment findings on the estuarine crocodile population in Sabah can be demonstrated and consequently provide management plans to establish whether, and subsequently ensure, sustainable utilisation and, ultimately, the survival of this species.