Scientific Research
Crocodiles
Ruchira Somaweera from the Reptile Ecology Research Lab of University of Sydney is currently based at Lake Argyle studying the Freshwater Crocodiles in the unique habitat of Lake Argyle.
Crocodile researcher Ruchira Somaweera inspects one of the reptiles at Lake Argyle. Picture: Nathan Dyer
Lake Argyle contains the highest density of freshwater crocodiles anywhere in Australia; spotlight surveys in 2010 estimated the non-hatchling population at 35,000 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 (bufadienalides), 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 the habitat degradation, accidental bycatch etc. Ruchira’s 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 minimize these impacts.
In order to put the results of this work into a general and reliable context, he’s trying to understand the biology of the freshwater crocodiles in Lake Argyle – aspects such as their diets, growth rates, 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 Ruchira is 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 pertubations on the persistence of populations. This research will provide some of this 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 his wife Nilu, personnel from Department of Environment and Conservation (DEC) and volunteers from Universities, Ruchira is spending his daytime studying freshwater crocodiles (with cameras and a GPS), mapping habitat characteristics, dissecting dead crocs (looking at the nasty things inside) and spotlighting during night.
For the latest update about crocodiles in Lake Argyle - go to http://au.news.yahoo.com/thewest/a/-/breaking/7916431/crocodile-para
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