Born in 1974 in southern Sudan, 41-year-old Nola died on 22 November 2015 at the San Diego zoo Jeff Keeton via Wikimedia Commons

With the death of a northern white rhino at the San Diego zoo on Sunday, there are just three of the species left on the planet at a sanctuary in Kenya. Efforts are on at both places to employ artificial reproductive techniques like test tube fertilisation and surrogate mothers to revive the species on the brink of extinction.

The authorities at the zoo are developing reproductive techniques where preserved genetic material from 13 northern white rhinos will be used to create embryos. These will be implanted in six female southern white rhinos who will act as surrogates. The two white rhino species are genetically distinct.

If successful, the technique could be applied to other rhino species, including the Sumatran and Javan rhinos — both also critically endangered.

Around 94 southern white rhinos, 68 greater one-horned rhinos and 14 black rhinos have been born at the zoo down the years. Nola, who was 41 years old, was battling many health issues and on Sunday (22 November) the authorities decided to euthanize the rhino. White rhinos can live up to 50 years.

First test tube rhino?

Conservation efforts are focused on the two female and one male northern white rhino at the Ol Pejeta Conservancy in Kenya where they are under strict protection against poachers.

Scientists plan to create the first test tube rhino using the sperm of the last remaining male northern white rhino, Sudan, and eggs from his two female partners. Sample vials have been frozen and stored in a zoo in the Czech republic.

The fact that the three failed to breed naturally prompted examinations by veterinarians who found the male's sperm count very low. The two female rhinos either could not get pregnant, or could not carry out a pregnancy to term.

A crowd-funding initiative seeks to raise the $750,000 (£494,000) required for the first rhino in-vitro fertilisation project. The fertilised eggs will be implanted into a surrogate southern white rhino female. "It's a race against time," Richard Vigne, who runs the Ol Pejeta wildlife park, told The Sunday Times.

But critics of the project believe it is too late for the northern white rhinos when the numbers are down to three.

The demand for rhino horn in Vietnam has resulted in more than 3,000 rhinos being killed by poachers in South Africa since 2010. The white rhino is particularly vulnerable to poaching, because it is relatively not as aggressive, and moves around in herds, according to WWF.

The northern white rhino could once be found in southern Chad, the Central African Republic, southwest of Sudan, northern Democratic Republic of the Congo (DRC), and northwestern Uganda. And in the 1960s, there were more than 2,000 remaining in the wild. After recovering partially in 2000 when there were around 30 numbers of the northern white rhino in the wild, the species was decimated by poachers. Southern white rhinos number around 10,000.