Last updated December 13, 2018 at 5:36 pm
Zoologists question the reliability of claims that ape numbers have increased.
Australian wildlife researchers have criticised a report by the Indonesian government, saying its estimate that orangutan populations increased by more than 10% from 2015 to 2017 is deeply flawed.
The experts, led by Erik Meijaard from the University of Queensland and writing in the journal Current Biology, say the results from Indonesia’s report are “scientifically unjustified” and the researchers used poor methodology, raising concerns about future protection for Bornean, Sumatran, and Tapanuli orangutans.
The report, The State of Indonesia’s Forest 2018, was prepared by the nation’s Ministry of Environment and Forestry (MOEF), with support from the Food and Agricultural Organisation and Norway’s International Climate and Forest Initiative and released earlier this year.
“All three species of orangutan are critically endangered and on a steep decline,” says Meijaard. “Their numbers are not increasing as indicated by the Indonesian government report”.
The report estimates that in 2015 there were 1153 orangutans at the nine monitored locations, and suggests that by 2016 there was more than twice that.
Meijaard and his colleagues point out “three major issues” with the findings.
First, “it is biologically impossible for an orangutan population to double its size in a year”, they write.
Second, some of the areas used for population sampling are relocation sites for orangutans, “implying that any net positive change in the monitored sites was inevitably preceded by at least an equally large negative change in non-monitored populations from which orangutans had been initially removed”.
Third, the monitored sites represent less than 5% of the Bornean and Sumatran orangutan range and represent none of the Tapanuli range.
Another problem with the data is that it doesn’t accurately represent the orangutan population. All the monitoring was done on protected national parkland, whereas most of the apes live in non-protected area, the scientists say.
“We believe that the current Indonesian government methods provide an unrealistically positive and biased picture of orangutan population trend,” they write.
The conclusions of the report could lead the government to fail to properly address conservation of its endangered species, the critics say.
“If the government thinks that orangutan populations are increasing, it calls for completely different strategies compared to those required for dealing with rapidly decreasing populations,” Meijaard explains.
“It is important that the government realises that populations remain in decline. Therefore, a new approach to orangutan conservation is needed.”
The scientists focus their criticism on the report’s estimates of orangutan populations, but note that the Indonesian government also estimates that numbers for 18 of its other 25 “priority species” increased by more than 10%.
The scientists find this claim dubious.
“This is not possible for some of the listed species, such as the Sumatran rhinoceros (Dicerorhinus sumatrensis), given known breeding rates and threat levels,” they write. “For the past several decades overall Sumatran-rhinoceros birth rates have been exceeded by death rates.”