SPOTTED TREE FROG – Litoria spenceri
Story by Michael Williams and Dr. Graeme Gillespie Bsc, PhD (All information and text is subject to copyright and cannot be reproduced without permission)
STATUS – CRITICALLY ENDANGERED
LOCATION – Central Victoria into New South Wales
“Some of the greatest battles fought to save life on earth begin with the smallest of interventions and sacrifice; testaments to compassionate individuals that cannot stand idle and bear witness to the relentless persecution of the defenceless”. – Michael Williams
DESCRIBING THE SPOTTED TREE FROG
The Spotted Tree Frog was first discovered and described as maculata by Professor Baldwin Spencer at the turn of the last century. The species was to be later renamed spenceri by Alain Dubois, after he established in 1984 the name maculata had previously been used to describe another species. A medium-sized frog, males are around 41mm (SVL – snout to vent length) with the largest of the species being the female at 52mm (SVL). The dorsal surface of individuals range in color from brown to green and is adorned with a reticulated pattern of dark brown patches. The underside of the animal is granular and can be either white or yellow with the groin area and hind limbs highlighted in orange. The species is restricted to the western fall of the Great Divide; from central Victoria to Mt. Kosciuszko in New South Wales where it occurs along upland streams between 280-1100 metres above sea level. The preferred habitat is montane riparian forest in and along rifle and cascade stream sections with exposed rock banks. This ideal environment supports the species in highly patchy communities along most occupied streams. Individuals are highly sedentary not venturing away from their sections of stream and documented evidence shows adults’ moving less than 80 metres along these transects over a period of several years. Breeding season for the Spotted Tree Frog takes place between early October to early December, but is largely variable due to seasonal conditions and individual populations. Eggs are deposited under large in-stream rocks with clutch sizes varying from 50 to nearly 1000 with an average of 500. Subsequent larval development occurs in shallow side pools or slow-flowing margins of stream over summer and autumn with metamorphosis taking place between mid-February and late March. Since its discovery, the species was encountered in only 19 streams and has always been considered rare. The species is now believed to be extinct in four of these streams and has substantially declined in distribution and abundance along most others with two populations dying out in the past five years.
A JOURNEY OF DISCOVERY
Dedicating the past 20 years of his life to studying the ‘Critically endangered’ Spotted Tree Frog, Melbourne based herpetologist Dr. Graeme Gillespie has been at the forefront of field research into this cryptic species sudden decline in the wild. Historical locations where the frog was known to occur in great numbers have been extensively surveyed by Dr. Gillespie and his colleagues throughout the past two decades in an attempt to map the current distribution and to determine the frog’s greatest threats. Dr. Gillespie’s extensive investigations have revealed many threats to the species survival, but none more devastating than predation by non-native fish species, such as North American Brown and Rainbow trout being introduced into the Australian environment. Like many introduced predators into foreign landscapes, the Brown and Rainbow trout has established itself incredibly well since it’s introduction into Australia in 1894; dispersing into most lakes, rivers, streams and other waterways by means of natural flows and in many cases through illegal introduction by reckless public individuals. Despite opportunities existing to secure important populations of this species from predation by removal of trout and the immediate construction of barriers to stop the fish entering known Spotted Tree Frog sites, the Victorian Government has ignored every attempt by Dr. Gillespie in addressing these issues for any of the areas where the frog is known to occur.
As well as predation by trout, the Spotted Tree Frog like many worldwide amphibian species is susceptible to infection from a fungal disease that has decimated populations worldwide. Chytrid fungus (Phylum Chytridiomycota), of which there are many different types, behaves very similar to the common cold or flu in that it becomes more aggressive, spreading with increasing intensity within larger, more dense amphibian communities. The Chytrid fungus attacks the keratin layer of the frog’s skin preventing it from absorbing oxygen eventually suffocating the infected individual resulting in a prolonged and agonizing death. Dr. Gillespie and his colleagues were to uncover one of the first outbreaks of the fungus within Australia during a five year survey of a population of Spotted Tree Frog surviving in great numbers within a remote area of Kosciuszko National Park; Dr. Gillespie recalls – “The area at Bogong Creek in Kosciuszko National Park is the perfect Spotted Tree Frog habitat. You had to be really careful where you placed your feet when walking for fear of stepping on one!” A seemingly healthy and abundant population, the Kosciuszko National Park frogs were completely wiped out by the aggressive fungus and sadly, many species of frog throughout Australia, now face the same bleak future at the hands of this killer.
Australia is known worldwide for its destructive bush fires. Much of Australia’s varying landscape is subject to such fires and many of its flora and fauna bear the full impact of these events. Dr. Gillespie has studied the many adverse effects of sediment loads into Spotted Tree Frog habitat and has concluded that all stages of the frog’s development are severely affected. Forest harvesting practices, road and bridge construction create varying levels of sediment loads into waterways, but it is fire events that cause the greatest amounts of load to enter the environment.
Surviving and breeding in and around forest streams, the Spotted Tree Frog is affected greatly by fire events, as immense deposits of ash is generated and continually dumped into nearby streams, completely asphyxiating most organisms that survive within these waters. Inevitably associated with such events, is the loss of ground cover, plants and trees. The integrity of soil is severely compromised and now, the once stable river banks give rise to continuing landslips that deposit incredible amounts of sediment load into the once pristine waterways, greatly impacting on all aquatic life. Tadpoles are such life, relying on macro-invertebrates as part of their diet, but now face a shortage of quality food vital for healthy growth and development.
Dr. Gillespie is the leading authority on frog conservation in Australia and Southeast Asia with over 25 years of experience in threatened species conservation and is highly respected throughout his field. With Dr. Gillespie’s vast knowledge and data on the Spotted Tree Frog collected over the past two decades, the species remains one of the most researched and endangered frogs in Australia.