The Critically Endangered Sumatran rhino (Dicerorhinus sumatrensis) recently made waves in the media after being found in the wild in Indonesian Borneo for the first time in 40 years. The excitement was short-lived, however, as the same rhino – a four-year-old female – died before she could be moved to a protected forest. The smallest of the rhinos, the Sumatran rhino was once numerous throughout Southeast Asia, but the species has suffered a catastrophic decline over the past 20 years. Today there are fewer than 100 individuals remaining.
A team of scientists from the Leibniz Institute for Zoo and Wildlife Research examined the historical decline of Sumatran rhinos in Borneo, exploring potential strategies to rescue the species from the brink of extinction. The reasons for the rhino’s diminishing numbers were poorly understood, but it is now believed to be down to a combination of poaching and low female fertility rates.
Poaching has driven Sumatran rhinos into tiny, isolated regions, with their numbers so low that females struggle to reproduce. “Females do not find a mating partner within the small isolated populations anymore”, explains Petra Kretzschmar, the lead author of the study, “the long non-reproductive periods lead to the development of reproductive tract tumours.” These sometimes football-sized tumours were present in a number of captured Sumatran rhinos in the past, and ultimately makes the females infertile.
The study used both current and past data to determine the probability that the population will go extinct within a given number of years. The analysis revealed that the percentage of breeding females and the period in which females could reproduce were key factors in the species decline. It also suggested that if no action is taken, these issues would make the extinction of the Sumatran rhino inevitable.
The scientists urge that measures must be introduced to prevent hunting and to stimulate breeding through assisted reproduction techniques. They recommended that remnant populations of 15 individuals or less should be relocated to highly protected areas, where conservationists can monitor the health of the population and carry out “reproductive management.”
Just two subspecies of the Sumatran rhino exist today, D. s. harrissoni in Borneo and D. s. sumatrensis in Sumatra. The Sumatran rhino in Borneo is almost extinct, with only one population known to conservationists. The female discovered in the wild earlier this year was found in Indonesian Borneo, but hopes to bring her into a captive breeding program were quickly dashed upon her death. “The captured animal was one of the last females of its species,” says Kretzschmar, “it died right after capture due to an infection of a snare wound.”
Rhino poaching remains a prevalent issue, with their horns highly sought after for use in traditional Asian medicines. This, in addition to the reproductive issues the animal has, means the task of saving them will certainly not be easy.
Kretzschmar P, Kramer-Schadt S, Ambu L, Bender J, Bohm T, Ernsing M, Göritz F, Hermes R, Payne J, Schaffer N, Thayaparan ST, Zainal ZZ, Hildebrandt TB, Hofer H (2016): The catastrophic decline of the Sumatran rhino (Dicerorhinus sumatrensis harrissoni) in Sabah: Historic exploitation, reduced female reproductive performance and population viability. Global Ecology and Conservation 6, 257–275. doi:10.1016/j.gecco.2016.02.006
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