A new report from Friends of the Earth suggests combined pressure from habitat loss, inbreeding and disease may pose significant threats to the survival of the koala in Victoria and South Australia.
The group is calling for federal protection for key populations of the species.
The death of koalas during logging of plantations across Victoria and South Australia has attracted international attention. A petition to the Victorian government by German environmental group Rainforest Rescue received more than 85,000 signatures after a report on ABC's 7:30 in July last year suggested many koalas had been killed during logging of plantations.
Friends of the Earth campaigner Anthony Amis told Green Left Weekly that the last endemic southern koala population in Victoria, in the Strzelecki Ranges to the south-east of Melbourne, “needs to be managed the same as animals that have federal protection in New South Whales and Queensland, they need to be treated as a separate management unit.
“Koala populations in the south-west of the state need management to look after their animal rights, so they don't suffer when plantations are logged. Their only protection at the moment is the state wildlife act,” Amis said.
Amis says there could be thousands of koalas in bluegum plantations in south-western Victoria and south-east South Australia. “Most of the bluegums were established after 1996. The biggest year of planting was around 2000 to 2001, and the trees are generally cut at about 10 to 12 years.”
Plantation companies appear to have improved practices after the TV exposure, but the report notes that these leave unanswered the question of what happens to displaced animals, once their habitat has been removed.
THE SAD HISTORY OF THE VICTORIAN KOALA
Friends of the Earth's report chronicles some of the sad history of the koala in Victoria and South Australia, after being nearly wiped out by hunters in the early 20th century. The history shows why, despite a rebound in numbers, the species still faces serious threats to its survival.
Most populations of koalas across Victoria and SA are descended from a mere handful that were saved from hunting in the early 20th century: a group of four that were translocated to Frenchs Island in Victoria, and another small group on neighbouring Phillip Island.
The only populations known to have survived in the wild, preserving a larger and more diverse gene pool, are in the Strzelecki Ranges. Other koalas in the two states are nearly all descended from the very small founder populations on French and Phillip Islands.
As the koalas bred and overpopulated the islands over the years, thousands of animals were translocated all over the state and have again overpopulated some regions, leading to starvation and population crash. These translocated populations are descended from the same handful of animals that lived in the early 20th century, what is known in genetics as a “bottleneck event”.
A HARD LESSON IN GENETIC DIVERSITY
Across Bass Strait, the Tasmanian devil is expected to become extinct in the wild within a couple of decades due to the devil facial tumour disease.
Devils were estimated to have numbers as high as 150,000 in the 1990s before the disease emerged, but these numbers were based on low genetic diversity after the population experienced a bottleneck event or events in the past, probably at least partly due to widespread hunting and poisoning in earlier decades.
While the exact historical details are lost, a severe lack of genetic diversity seems to be a major contributor to the lack of immune resistance to the disease.
Unlike the devils, who became extinct in mainland Australia 600 years ago, koalas do have larger, more genetically diverse populations in northern NSW and Queensland. But these are a different breed to the southern koala, which some scientists have even considered a separate subspecies.
No threat equivalent to the devastating but highly unusual devil facial tumour disease has emerged in southern koalas, but the low genetic diversity of much of the population still gives Amis cause for concern. “I don't think those translocated populations are going to be very stable, long term. Phillip Island in the 1970s and 80s had a big population, but it's now around 20 koalas,” Amis said.
The report includes information from animal carers, not yet subjected to formal scientific study and publication, documenting what may be congenital deformities in some of the translocated populations. One published scientific report has found that the Kangaroo Island population in SA has widespread testicular abnormalities, likely resulting from its extraordinarily narrow gene pool.
A widely reported koala disease is Chlamydia, which is transmitted sexually and from mothers to their offspring. A large percentage of koalas are infected, and the disease leads to many problems including infertility. Chlamydia has been implicated in the rapid decline of some koala populations in the past, but this is usually in combination with other stress factors such as habitat destruction.
In fact, koala populations established from the French Island refuge lack Chlamydia, and it is thought the lack of this disease is a factor leading to overpopulation and subsequent starvation in some translocated koala colonies. Amis thinks this “boom-bust” cycle has been accentuated through the planting of hundreds of thousands of hectares of new habitat in plantation industry areas.
SAVING DIVERSITY: PROTECT THE STRZELECKI KOALAS
the two endemic populations of the Victorian koala in Gippsland have been scientifically recognised as genetically distinct populations, with far greater genetic diversity than the translocated island populations. Yet no special conservation status is given to them under state or federal environmental law.
This is because existing conservation law only applies to threatened sub-species at the lowest level, not smaller sub-groups such as populations.
Southern koalas overall have high numbers, but the overall number obscures the many internal and external threats facing populations. It masks the real threat to the future of the Strzelecki koalas. The Friends of the Earth report details the survey work conducted on them.
“We're trying to get a handle on the possible size of the Strzelecki population,” Amis said. “I am taking a bit of a guess but I think it's under a thousand animals. There's a couple of hotspots where we have found 100-150 animals, but outside those the numbers are much lower.”
Amis blames “roadkill, logging, fire, and dog attack” in particular for a steep decline in numbers. “The 2009 fires knocked out about 40% of the animals – about 40% of the priority habitat got burned, including a lot of spots we knew that were chock-a-block with koalas. If you combine that with the logging, there's been a lot of habitat destroyed in the last 15 years or so. Over the last decade, perhaps a 50-60% reduction in numbers in the Strzelecki Ranges alone.”
The Strzelecki koalas are geographically and genetically close to the NSW populations, but according to Amis “the situation in southern NSW is quite dire.”
He said: “Koalas in the Strzeleckis and south-eastern NSW are related, they are basically the same animal, but I think there's about 20 koalas left in the Bega region. All the way from the south coast of NSW up to Wollongong I think there's only a few hundred animals.”
While the presence of the genetically diverse Strzelecki koala populations suggests that the southern koala could regain a healthy population size and gene pool, a lot still rests on how their habitat, including plantations, is managed, most crucially in the Strzelecki Ranges.
The ongoing habitat surveys are being conducted in a partnership between Friends of the Earth, Friends of Gippsland Bush and Rainforest Rescue. They have found two separate areas of Koala hotspots in the Strzeleckis, and the report notes: “The job now is to try and link up the 'islands' – if possible.”
As an account of the devil facial tumour disease by science journalist David Quammen grimly concludes, “the best time to cope with the problem of genetic impoverishment is before that problem occurs ... behind the genetic complexities, lie old truths we know well: keep habitat abundant and intact, and don’t let a species become rare.”
Now would be a good time to put those principles into practice for the southern koala.
[Download the report. Ben Courtice is a member of Friends of the Earth.]