Phone: 08 8984 9137
Fax: 08 8984 9139
Location: University of Sydney Tropical Ecology Research Facility, Middle Point Village, Northern Territory
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.
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.
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:
- 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.
- Hands-on training programmes for the general public with interactive demonstrations on snakes and presentations explaining the importance of snakes.
- Awareness programmes for school children between 4-9 yrs of age.
- 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.srilankanreptiles.com
||Bachelor of Science with 1st Class Honours
Department of Zoology, Faculty of Science, University of Peradeniya, Sri Lanka
|2008 onwards||PhD student
School of Biological Sciences, University of Sydney
|23.||Somaweera, R., Shine, R., Webb, J., Dempster, T. & Letnic, M. 2012. Why does vulnerability to toxic invasive cane toads vary among populations of Australian freshwater crocodiles? Biological Invasions: in review.|
|22.||Somaweera, R. & Shine, R. 2012. Crocodilian compromises: nest-site selection in a population of freshwater crocodiles with no access to sandy beaches. Austral Ecology: in review.|
|21.||Somaweera, R., Wijethilake, N. & Bowatte, G. 2012. Does the invasive shrub Ulex europaeus benefit an endemic Sri Lankan lizard? Herpetological Conservation and Biology: in review.|
|20.||Pizzatto, L., Somaweera, R., Kelehear, C. & Brown, G.P. 2012. Rhinella marina (Bufo marinus: Cane Toad). Prey. Herpetological Review: in review.
|19.||Somaweera, R., Brien, M. & Shine, R. 2012. When predators become prey: a review of predation on crocodilians. Herpetological Monographs: in review.|
|18.||Böhm, M., Somaweera, R. et al. 2012. The conservation status of the world's reptiles. Biological Conservation: in review.|
|17.||Somaweera, R. 2012. Unprovoked attacks by Australian freshwater crocodiles with a probable new case report from Lake Argyle in Western Australia. Australian Zoologist: in press.|
|16.||Somaweera, R. & Shine, R. 2012. Australian freshwater crocodiles (Crocodylus johnstoni) transport their hatchlings to the water. Journal of Herpetology: in press.|
|15.||Somaweera, R. & Shine, R. 2012. The (non) impact of invasive cane toads on freshwater crocodiles at Lake Argyle in tropical Australia. Animal Conservation: in press.|
|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.|
|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.|
|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|
|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|