A former CSIRO plant scientist has slammed the science behind the data used by the ACT government to justify the culling of eastern grey kangaroos, saying there were "significant deficiencies" in the review of the target density of kangaroos to promote biodiversity.
Dr William Taylor was giving evidence on day two of a hearing on the validity of the kangaroo cull before the ACT Civil and Administrative Tribunal, which Animal Liberation ACT is using to dispute the validity of a licence issued by the Conservator of Flora and Fauna to conduct the cull.
The protestors are arguing the decision to issue the licence was based on false data and would not help the environment.
Dr Taylor gave evidence, citing his credentials as a former Assistant Professor of Genetics at the University of California, Berkeley before joining the CSIRO as a research scientist in 1987, and as a former editor of the International Journal of Plant Sciences.
While the cull is designed to protect plant species from overgrazing by kangaroos, Dr Taylor said he initially became involved in looking at the research behind it when he was "horrified by what was being passed off as science" when it came to an experiment by the Friends of Mount Majura group "purporting to show the effect of grazing by kangaroos and rabbits".
In relation to a review on sustainable kangaroo density estimates,Dr Taylor questioned how the researchers concluded the optimum kangaroo density was one per hectare with an "almost complete lack of evidence".
He said while the review measured the effect of grazing on biomass, it didn't make any connection with biomass and biodiversity.
"In some cases, grazing by kangaroos is a good way to control weed species," he said.
Also appearing on day two of the hearing, which is expected to last four days, was Raymond Mjadwesch, a consultant ecologist, who disputed that kangaroo populations are increasing at the rate claimed in scientific reports the Conservator is referencing to authorise the cull.
Mr Mjadwesch said the assumed rate of population growth referenced in the Territory's kangaroo management plan of 20 per cent was "a wrong estimate", and claimed a normal growth rate would be more like 10 per cent.
He said a graph purporting to show the rate of increase in one area had to be based on a flawed counting methodology, as the claimed rise in population was "biologically impossible or implausible".
"If you look at the biology of the species, these graphs make no sense," Mr Mjadwesch said, claiming it didn't take into account the 70 to 75 percent mortality rate for joeys.
Dr Donald Fletcher, an ACT government senior ecologist whose research informed the graphs, defended his counting methodology, which he said used a large number of people in a relatively small area, in this case one secured by a fence preventing the migration of kangaroos in or out.
He said actual observations showed the rate of population increase was possible to be higher than the theoretical rate of increase, which assumes an even spread of ages and a steady food source.
He said it was possible to grow higher with a female bias in the population.
"We have abundant evidence from a variety of sources ... that the eastern grey kangaroo achieves a wide range of growth in practice," Dr Fletcher said.