Ruchira Somaweera Tropical Ecology Research Facility Middle Point, NT Ph: (08) 8984 9137 Fax: (08) 8984 9139 e-mail: ruchira.somaweera@gmail.com Websites: http://www.pdn.ac.lk/socs/zaup/reptiles/ruchira.html http://www.phylodiversity.net/bb07/students/ruchira/

Current Research Past Research Education Publications Presentations Grants and Awards

Effects of fishing and cane toads on the freshwater crocodiles at Lake Argyle, Western Australia 

Lake Argyle contains the highest density of freshwater crocodiles anywhere in Australia; spotlight surveys in 1989 estimated the non-hatchling population at 25,000 animals. Viability of crocodile populations in the Lake (and elsewhere) is threatened by the imminent arrival of invasive (toxic) cane toads. Because Australia has no native toads, many Australian predators, including freshwater crocodiles, lack physiological resistance to toad toxins (bufadienolides), and die if they attempt to eat toads. Substantial mortality of freshwater crocodiles has been documented at the toad invasion front, and Letnic, Webb and Shine (in the journal Biological Conservation 2008) recently reported that population densities of crocodiles declined by up to 77% following toad invasion on the Victoria and Daly Rivers. If a similar decline occurs at Lake Argyle, it may result in the total collapse of the crocodile population, an impact vastly greater than any attributable to habitat degradation, accidental bycatch etc. My doctoral research focuses mainly on predicting and measuring the impact of cane toads on freshwater crocodiles at Lake Argyle, and on developing new ways to minimise these impacts.

In order to put the results of this work into a general and reliable context, I am trying to understand the biology of the freshwater crocodiles in Lake Argyle – aspects such as their diet, growth rate, reproductive biology and so forth. Currently there is very little reliable information on these topics with regard to crocodiles in a vast stagnant water body, therefore I am studying the current population of crocodiles at the Lake before the toads arrive, in order to understand their life histories (feeding, growth, maturity and reproduction etc.) and habitat usage along the shoreline to identify areas, and identify which life stages of crocodiles may be more vulnerable to toads (for example, what sizes of crocodiles eat native frogs, and so are likely to take toads also?). Management of long-lived animals such as crocodiles requires data on age structure, growth, maturity, and the effects of perturbations on the persistence of populations. This research will provide some key data before toads invade and have a major impact on the crocodiles at the Lake. This data, together with data on other aspects will provide managers with solid and reliable information to model (and hopefully, mitigate) the impacts of toads on crocodiles and will ultimately lead to better management of freshwater crocodiles in Lake Argyle.

With the help of members from the Cane Toad Group of the Department of Environment and Conservation (DEC), my wife Nilu, and volunteers from Universities etc., I am spending my days hunting for crocs (with cameras and a GPS), mapping habitat characteristics, dissecting dead crocs (looking at the nasty things inside), and spotlighting at night.

 

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Past Research

Gecko reproduction

For my Bachelor’s degree research project, I investigated the egg-laying strategies of the Kandyan day-gecko (Cnemaspis kandiana) in rock caves at Gannoruwa Forest Reserve in Sri Lanka. Ecological studies on Sri Lankan geckos are very few in number, thus my study helped to increase the knowledge on reproductive behaviour and biology of this endemic gecko, and revealed that it is another species engaged in communal nesting, adding its name to the list of the other nine communal nesters (out of the 51 described species) of this Old World gecko genus. The study was intended to address issues such as the breeding habitats and the environmental conditions preferred by C. kandiana, different aspects of its oviposition and reproduction, its interactions with other species in the nesting habitat and to check whether this species is actually practising communal nesting or whether there is only a situation where a single female lays multiple clutches at a single location.

 

Snake conservation work

Me, my wife (Nilu) and my colleagues back in Sri Lanka, strongly believe that successful conservation of Sri Lankan snakes can ONLY be achieved if the conservation efforts are backed by strong and scientific programmes to help raise public awareness, and encourage the involvement of the general public in conservation activities.

As an animal group, snakes cause the highest number of human deaths in Sri Lanka, where annually ~150 out of ~30 000 victims die. Thus, snakes are ruthlessly over-killed through fear, misidentification, poor knowledge and as a precautionary measure against snakebite. Our studies indicated that from 1-13 snakes per week are killed in the ten villages we studied over the past year. Given this situation, the conservation and management of snakes in Sri Lanka must be backed by strong educational programmes and public awareness campaigns which we were actively conducting.

Some of our work involved:
1. Awareness programmes for the general public about, a) how to make human premises snake-proof, b) how to remove a snake if found in a house, c) precautions and first aid in case of a snake bite.
2. Hands-on training programmes for the general public with interactive demonstrations on snakes and presentations explaining the importance of snakes.
3. Awareness programmes for school children between 4-9 yrs of age.
4. Dissemination of information by distributing copies of a poster on identifying venomous snakes and a local-language field guide on snakes.

The project resulted in the publication of the first comprehensive local language guide to the snakes of Sri Lanka, aimed at both amateurs and specialists. It described and illustrated all the 98 species of Sri Lankan snakes, both terrestrial and marine. See http://www.pdn.ac.lk/socs/zaup/reptiles/snakebook.htm

 

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Grants and Awards

2009	IUCN-SSC Crocodile Specialist Group Student Research Grant
2008	Association for Tropical Biology and Conservation travel grant to Kuching, Malaysia
2008	Endeavour International Postgraduate Research Scholarship (EIPRS)
2008	Endeavour Postgraduate Award (EPA)
2008	International Postgraduate Award (IPA), University of Sydney
2008	Australian Leadership Award
2007	Centre for Tropical Forest Science and the Arnold Arboretum (CTFS-AA) travel grant for the Harvard Summer School in Borneo
2007	Miriam Rothschild Bursary from University of Cambridge for an internship at the Natural History Museum in London
2007	Professor Felix Prashantha Amerasinghe memorial gold medal for excellence in Zoology, University of Peradeniya
2007	University award for academic excellence, University of Peradeniya

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