Koala population on St Bee’s island draws scientists to study fluctuations in numbers – ABC

By September 6, 2022 News

ABC Tropical North / By Hannah Walsh
Posted 4 Sep 2022

The koala population on St Bee’s Island is recognised around the world. (Supplied: Department of Environment and Science)
On a tropical island in North Queensland, an iconic marsupial lives its best life away from predators.
Despite being listed as endangered in February, on St Bee’s Island the koala does not die from land clearing, being hit by a car, eaten by a dog or disease.
In fact, what regulates the population, which can fluctuate up to 200 per cent some years, remains mostly a mystery.

This year it is estimated there are around 100 koalas on the island. (Supplied: Bill Ellis)
The fate of the colony has been measured by researchers since the late 1990s and has received interest from around the globe.
Scientists from Central Queensland University, the University of Queensland and the Department of Science have just returned from a week-long trip trekking the island in search of the Aussie icon.

The team from the Department of Environment and Science with Alistair Melzer (right) from Central Queensland University. (Supplied: Department of Environment and Science)
It is hoped in years to come, this survey will be done solely using drone technology, which is already being trialled, and thermal imaging.
Climate factors considered
St Bee’s Island is about 38km offshore from Mackay. The secluded national park is characterised by hilly terrain and dense grassland.
CQU researcher Alistair Melzer travels to the island at least once a year to survey the world-famous koala population.
“We walk in a systematic way across the landscape and collect information on the koalas we see,” Dr Melzer said.
“The pattern we’re seeing of population increases and declines seems to be associated with broad climatic indices.
“The exact cause on this island we haven’t yet worked out and that’s ongoing research.”

A team from CQU and UQ spent the week combing the island and catching koalas.
(Supplied: Department of Environment and Science)
He said the population had had two peaks and two declines over the 20-year period he had been visiting the island.
“At the moment, we’re at the bottom of one of those declines,” he said.
“The peaks we recorded were around 300 and 350 animals and that was in 1999 and 2010.
“The troughs have been around about 100 or so animals … in 2003 and now.”
Dr Melzer said his team would keep monitoring to see if the population built back up.
“The koalas we see appear very healthy … so we’re pretty sure it has nothing to do with disease,” he said.
“We think it’s something in the condition of the forest within which they’re living and that would tie in with climatic variability.”

St Bee’s Island is off the coast of Mackay.(Supplied: Department of Environment and Science)
UQ ecological researcher Bill Ellis said having an understanding of exactly what regulated the population was an important question.
“My little team is mostly involved in surveying and catching the koalas in a particular area of the island,” he said.
“We’re looking at population dynamics … rates of reproduction, health and those kinds of things.
“We mark every individual with an ear tag so every year when we go back we can find out if we’re seeing new individuals or the same from previous years.”
Dr Ellis said a number of cyclones and dry years had had a big impact on the population.
“We think this is potentially pointing to another impact on the mainland, which is that climate has a pretty significant impact,” he said.
“We know in the south-east, cars and dogs are a massive issue … and disease.
“But underlying all of that, it’s the environmental conditions.”
Maintaining habitat
A small team from the Department of Environment and Science also attended the latest research trip.
Ecological assessment manager Rhonda Melzer said their goals involved maintaining koala habitat, recovering ecosystems and using fire-adapted ecosystems on the island.
“We want to maintain the koala habitat on the island and part of doing that in the long term is to promote seedling regeneration, in particular blue gums,” she said.
“Unlike some islands off the coast of say Victoria and South Australia, where there’s been really significant impacts on the habitat from koalas because they’ve bred up and eaten themselves out of house … that hasn’t happened on St Bee’s.”
St Bee’s was a grazing property for many years and formally became national park in 2001.

Thermal imaging from drones is used to count koalas on the island. (Supplied: Department of Environment and Science)
Comparing populations
Dr Alastair Melzer said the bigger picture in Queensland was mixed.
“In the western edge of the animals’ distribution, there has been significant localised extinctions generally associated with big droughts,” he said.
“In hill and ranges areas of the region … the populations are persisting.
“In some areas around Capricornia there’s a suggestion that koala populations are resurging, but very slowly and at low density.

Koalas are considered an endangered species in NSW, Queensland and the ACT. (ABC North Queensland: Chloe Chomicki)
“In south-east Queensland … the most abundant population … they’re under significant pressure because of the amount of urbanisation and the intensification of infrastructure that’s going on.”
Dr Ellis said there was not one clear solution across all populations of koalas.
“We need different solutions in south-east Queensland to what we have in Central Queensland and at the borders of their population.”