Ruchira Somaweera


PhD student 2008-2012

Current Email:


Shine Lab Research

Biology and Conservation of Freshwater Crocodiles at Lake Argyle, Western Australia


Lake Argyle contains one of the largest populations 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 and understanding the pathways by which populations could recover.

freshie swimming

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, permanent and a stagnant water body, therefore I am studying the current population of crocodiles at the lake, 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 volunteers from universities etc. and members from the Cane Toad Group of the Department of Environment and Conservation (DEC), and the with the support from community groups such as Stop The Toad Foundation (STTF), Kimberley Toad Busters (KTB) and Save The Endangered East Kimberley Species (SEEKS), 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.

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



 Year  Qualification
2002-2006 Bachelor of Science with 1st Class Honours
Department of Zoology, Faculty of Science, University of Peradeniya, Sri Lanka
2008-2012 PhD
Biological Sciences, University of Sydney


 #  Publication details
23. Somaweera, R., M. Brien, and R. Shine.  2013.  The role of predation in shaping crocodilian natural history.  Herpetological Monographs: in press.
22. Somaweera, R., R. Shine, J. Webb, T. Dempster, and M. Letnic.  2013.  Why does vulnerability to toxic invasive cane toads vary among populations of Australian freshwater crocodiles?  Animal Conservation 16:86-96.
21. Somaweera, R., and R. Shine.  2013.  Nest-site selection by crocodiles at a rocky site in the Australian tropics: making the best of a bad lot.  Austral Ecology 38:313-325.
20. Somaweera, R., Wijethilake, N. & Bowatte, G. 2012. Does the invasive shrub Ulex europaeus benefit an endemic Sri Lankan lizard? Herpetological Conservation and Biology 7:219-226.
19. Pizzatto, L., Somaweera, R., Kelehear, C. & Brown, G.P. 2012. Rhinella marina (Bufo marinus: Cane Toad). Prey. Herpetological Review: in review.
18. Böhm, M., Somaweera, R. et al. 2013. The conservation status of the world's reptiles. Biological Conservation 157:372-385.
17. Somaweera, R. 2011. Unprovoked attacks by Australian freshwater crocodiles with a probable new case report from Lake Argyle in Western Australia. Australian Zoologist 35:973-976.
16. Somaweera, R. & Shine, R. 2012. Australian freshwater crocodiles (Crocodylus johnstoni) transport their hatchlings to the water. Journal of Herpetology 46:407-411.
15. Somaweera, R. & Shine, R. 2012. The (non) impact of invasive cane toads on freshwater crocodiles at Lake Argyle in tropical Australia. Animal Conservation 15:152-163.
14. Somaweera, R., Webb, J. & Shine, R. 2011. It’s a dog-eat-croc world: dingo predation on the nests of freshwater crocodiles in tropical Australia. Ecological Research 26:957-967.
13. Somaweera, R., Crossland, M.R. & Shine, R. 2011. Assessing the potential impact of invasive cane toads on a commercial freshwater fishery in tropical Australia. Wildlife Research 38:380-385.
12. Somaweera, R., Webb, J. & Shine, R. 2011. Determinants of habitat selection by hatchling crocodiles (Crocodylus johnstoni). PLoS ONE 6(12):e28533.
11. Somaweera, R., Webb, J., Brown, G.P. & Shine, R. 2011. Hatchling Australian freshwater crocodiles rapidly learn to avoid toxic invasive cane toads. Behaviour 148:501-517.
10. Somaweera, R., Somaweera, N. & Shine, R. 2010. Frogs under friendly fire: how well can Australians distinguish native frogs from invasive cane toads? Conservation Biology 143:1477-1484.
9. Somaweera, R. & Somaweera, N. 2010. Serpents in jars: the snake wine industry in Vietnam. Journal of Threatened Taxa 2(11):1251-1260.
8. Somaweera, R. 2009. Observations on the reproductive ecology of the Kandyan Day Gecko, Cnemaspis kandiana, in Gannoruwa Forest Reserve, Sri Lanka. Journal of the National Science Foundation of Sri Lanka 37(1):13-22.
7. Somaweera, R. & Somaweera, N. 2009. Lizards of Sri Lanka: A Colour Guide with Field Keys. Chaimaira Publications, Germany: 304pp.
6. Somaweera, R. & Somaweera, N. 2009. An overview of Sri Lankan sea snakes with an annotated checklist and a field key. Taprobanica 1(1):43-57.
5. Smith, E.N., Manamendra-Arachchi, K. & Somaweera, R. 2008. A new species of coralsnake of the genus Calliophis (Squamata: Elapidae) from the Central Province of Sri Lanka. Zootaxa 1847:19-33.
4. Somaweera, R. & Das, I. 2008. Lepidodactylus lugubris (Mourning Gecko) in Malaysia: Sarawak. Herpetological Review 39(3):368.
3. Somaweera, R., Ukuwela, K. & Alagoda, T. 2006. A note on specimens of Gerarda prevostiana (Colubridae: Serpentes) collected from Sri Lanka. Ceylon Journal of Science (Bio. Sci.) 35(1):91-93.
2. Somaweera, R. 2006. Sri Lankawe Sarpayin (‘The Snakes of Sri Lanka’). Wildlife Heritage Trust of Sri Lanka: 297pp.
1. Somaweera, R. 2006. Defensive posture in Kaloula taprobanica Parker (Microhylidae: Amphibia). Journal of the Bombay Natural History Society 103(1):108-109.

Conference Presentations

 Year  Conference details
2011 Dingo predation on the nests of freshwater crocodiles in tropical Australia. Annual Conference of the Ecological Society of Australia, November 2011, Tasmania, Australia.
2011 Parental care behaviour of freshwater crocodiles in tropical Australia. 2011 Conference of the Australian Society for the Study of Animal Behaviour, April 2011, Adelaide, South Australia.
Impact of cane toads (Bufo marinus) on freshwater crocodiles (Crocodylus johnstoni) at Lake Argyle, Western Australia. Student Conference on Conservation Science, Bangalore, India.
2010 Evolutionary impacts of invasive cane toads on Australian crocodiles. 2010 Annual International Meeting of the Association for Tropical Biology and Conservation, Bali, Indonesia.
2010 Cane toads and freshwater crocodiles in Lake Argyle. 2010 Kimberley Environmental Forum, Kununurra, WA. Australia.
2008  “Alien vs Predator” – a case study of helping snakes by helping people around a tropical forest in Hantana, Sri Lanka. Proceedings of the ATBC Confenece “Towards sustainable land-use in tropical Asia”, Kuching, Malaysia.
2007 Climatic change, habitat loss or mere over-killing? What causes the extinction of Sri Lankan snakes? Proceedings of the Student Conference on Conservation Science, University of Cambridge, UK.
2006 Geckos on the move: how humans have influenced the distribution of Hemidactylus geckos in Sri Lanka. Abstract of the International Conference on Humid Tropical Ecosystems: Changes, Challenges & Opportunities, Kandy, Sri Lanka.
2001 A comparison of amphibian diversity in Kandyan home garden agro-ecosystems of central Sri Lanka. 4th World Congress in Herpetology, Sri Lanka.
2001 Biodiversity of the Bundala National Park and Ramsar wetland. 7th Annual Forestry and Environment Symposium 2001, Sri Lanka.

Guest Lectures and Seminars

Year Lecture/Seminar
2011 It's hard being a freshy: natural history of freshwater crocodiles at Lake Argyle in east Kimberley. NT Field Naturalists Club, Charles Darwin University, Australia, 9 March 2011.
2011 Survival fitness of freshwater crocodiles in tropical Australia. University of Sydney Tropical Wildlife Ecology and Management Course, Darwin, Australia, 15 February 2011.
2010 A tale of a toad and a croc: cane toads and freshwater crocodiles in Lake Argyle. Department of Biological Sciences, National University of Singapore, Singapore, 10 March 2010.
2010 Sex in the croc world: reproductive ecology of freshwater crocodiles. University of Sydney Tropical Wildlife Ecology and Management Course, Darwin, Australia, 17 February 2010.
2008 Myths & reality – the snake fauna of Sri Lanka. Wayamba University, Sri Lanka, June 2008.
2008 Conservation of snakes in Sri Lanka. Kandy Nature Club, Sri Lanka, April 2008.
2006 Biodiversity and its conservation. University of Peradeniya School Science Camp programme, Ratnapura, September 2006
little freshie

Grants and Awards

 Year Award
2011 Finalist at 2011 Postgraduate Excellence Award, The University of Sydney
2011 Chicago Board of Trade Endangered Species Fund grant. Project title: Usage of traditional knowledge to minimize human-crocodile conflict and conserve crocodiles in Sri Lanka
2011 National Geographic Society Research and Exploration grant. Project title: Evolutionary ecology of the endemic horn lizards of Sri Lanka
2011 University of Sydney Postgraduate research support travel grant
2010 University of Sydney Postgraduate Research Support Grant
2010 University Research Grant from Wildlife Preservation Society of Australia Inc.
2010 Indian National Centre for Biological Sciences Travel Grant to India
2009 University of Sydney Postgraduate Research Support Grant
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
freshie underwater