Tasmania’s ecology is now unstable – feral cats, disease in wildlife populations, climate change and habitat loss are progressively reducing the island’s biodiversity. In 1996 the Tasmanian Regional Forest Agreement documents cited research describing the Tasmanian devil population as overabundant and estimated its size at between 130,000 and 170,000 animals (an astonishing number of devils, amplified by the tens of thousands of 1080-poisoned marsupial bodies left in the bush and around farm edges).
This was the year that the transmissible facial cancer was first detected in north-east Tasmania. In 2009 a discussion paper prepared by DPIPWE to support the Cat Management Act 2009 stated that there were 92,000 pet cats and about 150,000 feral cats in Tasmania. In 2012, the new Invasive Species Unit is now claiming that ‘the feral cat population had increased at an alarming rate in recent years and was wreaking havoc on the ecosystem’. (Sunday Examiner 13 May 2012 page 20). So in 2012 devils are in decline and feral cats only just recognised as a problem for Tasmania’s biodiversity.
TCT’s Biodiversity Campaigner Jennifer Rowallan has put the cat-transmitted disease, toxoplasmosis front-of-stage in the Trust’s ongoing advocacy for biodiversity conservation (The Tasmanian Conservationist March 2012 no. 235, ‘Toxoplasmosis – A cat disease that Tasmanians should be concerned about’. The disease is now well established in Tasmania; in fact, Tasmania has one of the higher Toxoplasma exposure levels in mammals precisely because we have so many cats and the environment favours the long-term survival of these microscopic parasites in soil and through the faunal food chain.
The impact of toxoplasmosis on free-ranging wildlife was first identified in Tasmania almost 30 years ago and, in the days when the Department of Primary Industries actually took an interest in monitoring the disease in sheep flocks as well as wildlife, some useful research was done. The reality is that, whilst ever there are cats (Felis catis) in urban, rural and natural environments in Tasmania, all warm-blooded fauna (humans, marsupials and birds) are at risk of exposure and we must live with this parasite. Toxoplasmosis is a disease that Australian fauna had no contact with prior to the introduction of cats with human settlement. The sheer number of free-ranging cats in Tasmania and the longevity of Toxoplasma oocytes’ survival in the environment lead to the disease being a threatening process for the survival of some species of marsupials and responsible for seasonal mortalities of a number of others. The eastern-barred bandicoot (Perameles gunni) is particularly affected by toxoplasmosis which continues to kill these bandicoots.
Detecting a wildlife disease always relies on awareness amongst the general public and a willingness of the animal disease infrastructure in Tasmania’s government to respond. Sadly, due to cost-cutting, much of the veterinary practitioner surveillance for new and emerging disease was terminated about two years ago; useful capability to test and report diseases in wildlife was curtailed dramatically. This came at the same time that University of Tasmania (UTAS) wildlife researchers were going to scientific conferences and speaking about the unprecedented declines in eastern quoll (Dasyurus viverrinus) populations across Tasmania. In March 2012 Mercury journalist Helen Kempton interviewed UTAS zoologist Chris Johnson. He said: ‘Eastern quoll numbers also appear to be on the way down and cats – either eating or stressing populations [of eastern quoll] – is one of the theories behind their demise. The [eastern] quoll is also being impacted by the hidden threat of toxoplasmosis which is transmitted by cats’. In May 2012 Bronwyn Fancourt, a PhD zoology student nominated the eastern quoll for listing as a threatened species under Tasmanian legislation, citing feral cat predation and disease as potential factors in the 60 per cent decline over the last decade.
Recently the decline of the larger spotted-tailed or tiger quolls (Dasyurus maculatus) in Victoria was also linked to toxoplasmosis. Speaking of the demise of the Victorian tiger quoll, biologist and nature writer Leonard Cronin told ABC Radio National, ‘…they put a bounty on their heads so people used to come in and shoot them, poison them and the population declined dramatically and then they got infected with a parasite called toxoplasmosis and that really damaged the population so now they are endangered basically’ (‘Confirmed tiger quoll sighting raises hopes of naturalists’, ABC The World Today program, Monday 12 May 2012).
Several small dasyurids such as Antechinus, Sminthopsis and Planigale spp., are susceptible to this parasite, particularly when they are immune-suppressed or become infected in captivity. Further work is needed to determine whether the disease toxoplasmosis is actually responsible for quoll declines or whether there are any other causes for the loss of quolls in eastern Australia. One thing is certain, ignorance about the impact of toxoplasmosis is not bliss for Tasmania!
David Obendorf
Wildlife Veterinarian