Sustainable harvesting of kangaroos
From the November 2008 edition of Agriculture Today.
Theory behind harvesting
If some animals are taken out of a population, the resources that those animals would have consumed become available to the animals that remain.
Since resources may then be less limited, the fecundity of individuals is enhanced and mortality is reduced.
The population compensates for the harvested animals.
However, if the rate of removal is too high, the population will be unable to compensate and will slide to extinction if harvesting continues.
Sustainable use is the use of biological resources in a way and at a rate that does not lead to the long-term decline of biological diversity, maintaining potential to meet the needs and aspirations of present and future generations.
Sustainability of commercial kangaroo harvesting relies on their populations not exhibiting long-term declines that might compromise their viability.
Ecologically sustainable harvesting seeks to take animals at a rate within the capacity of species and their habitats to maintain themselves.
The available evidence strongly supports the claim that under the current harvest rates and strategies, commercial kangaroo harvesting is ecologically sustainable.
All viable populations are capable of net growth.
Under favourable conditions births will exceed deaths and a population will have net growth.
However, even populations that are undergoing a temporary decline, such as during a drought, can be harvested sustainably.
Extensive modelling studies that simulate kangaroo populations in a natural environment have demonstrated that sustainable harvesting can occur during and after a major drought.
These results are supported by the long-term kangaroo monitoring programs undertaken by each State agency responsible for managing the commercial harvest.
Kangaroo harvesting is not constant across the landscape, but very patchy.
Many areas on co-operative properties will be inaccessible to harvesters, with low to no culling.
At a regional scale a different pattern emerges.
Most kangaroo harvesting is concentrated around sites that have chillers to store carcases for the meat trade.
On a regional scale, areas located more than approximately 100 kilometres from a chiller box have low rates of harvesting.
Kangaroo harvesting is regulated by controlling the numbers taken under a variable quota system that holds harvest rate relatively constant and is set as a proportion of the population size - called a proportional harvest strategy.
This strategy relies on an accurate estimate of population size and allows adjustments in the quota that tracks population trend.
While it is expensive to implement, it provides information on the state of the population size and trend (growing, declining or stable), which is then used to determine future quotas.
This takes into account variation in the environment, and consequently variation in the kangaroo population.
The proportional harvest strategy is simple yet robust, used for many wildlife harvests around the world, with a track record for sensible management.
Dr Steve McLeod is a NSW DPI kangaroo specialist livestock research officer who, with colleague Dr Ron Hacker, produced a report for the Murray-Darling Basin Commission in 2004 that quantified the impact of sex selective harvesting on kangaroo populations, which became the basis for the Kangaroo Management Options Report and for their book, Living with Kangaroos.
