Map shows Pobassoo and Astell Islands off Arnhem Land, where the
quolls were released.
In 2003, 64 northern quolls (Dasyurus hallucatus), taken
from sites across the Northern Territory were released on two
islands in the English Company group off north-east Arnhem Land
(see map right). This translocation aimed to save these small
carnivorous animals from the threat of cane toads which, through
poisoning quolls that tried to eat them, were having a catastrophic
impact on mainland quoll populations.
Recent monitoring of these island quolls has shown there are now
between 5600 and 6200 adult females—a remarkable increase in
numbers. This appears to be good news for the quolls and raises
some questions: why are they doing so well? Are these populations
The translocation and release of the quolls was carried out by
the Gumurr Marthakal Rangers, the Traditional Owners of the
islands, Traditional Owners from where the quolls were sourced,
scientists from the NT Department of Natural Resources and the
Arts, the Territory Wildlife Park and Parks Australia North.
Martin Armstrong, NT Parks & Wildlife, during the original
release in 2003. From the original population of 64 quolls, numbers
have grown to more than 5000. Photos: Ian Morris
Nineteen quolls were released on Pobassoo Island and 45 on
Astell Island in February and March 2003.
These islands were selected because they had rocky sandstone
habitats favoured by quolls, no human settlements and a low risk of
invasion by toads. Also, there were no other animal species that
the introduced quolls would likely have significant negative
Astell and Pobassoo islands were also thought to be large enough
for quoll populations to survive for at least 30 years—long
enough, hopefully, to have worked out solutions to the threat posed
by cane toads to quolls.
Working out how many quolls are now on the islands is not that
easy; you can’t count each one, so a small sample needed to
be trapped and then the total population estimated.
Depending on the likely ‘catchment area’ of each
trap, the population estimates in December 2007 varied from around
4800 to 5300 quolls on the larger Astell Island and from around 820
to 900 quolls on the smaller Pobasso Island.
These numbers (from December, 2007) refer only to adult female
quolls as after an exhausting mating in the dry season, virtually
all the males die, while the young remain in the den for around
4–5 months, so total numbers of quolls would be more than
these figures suggest.
It is thought the quolls are doing well for a couple of reasons,
the first one being that there are no toads around to poison quolls
that try to eat them.
But these populations are higher than those measured for
mainland quolls even before the toad invasion, and a major reason
for the success of the translocation is suspected to be the lack of
predators such as feral cats.
Interestingly, shortly after the translocation, much of Astell
Island was burnt by fire and in 2005 the vegetation of both islands
took a pounding from Cyclone Ingrid.
These quoll population densities will presumably level out or
drop as they are larger than any known natural population density,
but there is no sign yet that the crowded conditions are having any
ill-effects on the animals. The trapped quolls were in good
condition, the populations had healthy genetics and breeding
success continues to be good.
— Peter Jacklyn.