Gorillas are declining rapidly in the wild and our role as a zoo is to maintain a safety net of animals in human care. Right now the problem with most of the animals we are dealing with is not a lack of tigers, it is a lack of habitat for tigers.
We could breed the hell out of the tigers we have right around the world but we can't because we haven't got enough zoos to hold them. You would put more pressure on the surviving animals in the wild by releasing zoo-bred animals adding to their numbers.
Our current male gorilla, Kibabu, is 35 and has created 14 offspring. With these breeding programs the idea is that you have an equal contribution of genetic material from every living animal in the population.
By the time you have produced 14 different individuals, you have really done your dash. He is of an age that in the wild he would already have been ousted by a young and up-and-coming male.
To start to find a replacement, we go to the international gorilla stock book: we need to know exactly who's who. For every animal in zoos around the world, there is an original traceback to an animal that came from the wild. To know ''who begat who'' is vital, so that there's no inbreeding.
There are breeding software programs specially developed for zoos so I can see the ''relatedness'' of every individual. I can search the studbook software to get all the males born between certain years still living in their natal group and whose father has been a good role model. We look at genetics and behaviour.
I ended up with a shortlist of five males, all of which were as unrelated as possible to any other gorilla in this part of the world. You can use the software to create pretend babies and you can check that the inbreeding is zero.
I then went with our senior keeper to Austria, France, Britain and the Netherlands just to observe the behaviour of the five on the shortlist. We didn't want an animal that was unsociable or shy and retiring - we wanted the gorilla in the gorilla.
In France at The Valley of the Monkeys, near Bordeaux, it was like looking at our own group in terms of behaviour and calmness. If you know your gorillas, it only takes a couple of hours to come to a decision. It's a bit like if your daughter has a new teenage boyfriend. You watch him with his family for two hours - you get a pretty good idea of his demeanour.
After we had visited all the animals on the shortlist we went back to the hotel and decided with the head keeper that we should write down our top two in order of priority and then swap pieces of paper. They were both the same.
Eleven-year-old Kibali arrived in January, and is behaving in the way we hoped he would. He has mated with a young female, Kimya, a few times now, but we don't think she is pregnant. I think it is going to take a few months. We also do urine tests with a pregnancy testing stick and send samples to our reproductive lab in Dubbo. We are hopeful that they will produce offspring which will help protect the future of gorillas.
There is also a lot that humans can do to help. Recycling old mobile phones reduces demand for minerals found in gorilla habitat, such as coltan, a metallic ore found in central Africa which is the habitat of the gorilla.
The mining is an issue in itself but it's the roads they put in that add to the problem. Suddenly, the poaching of gorillas becomes easier and we are arriving there with our human diseases.
Recycling your mobile phone really can help: it reduces the need to mine this ore and the phones can be refurbished and resold, raising money to help protect the gorilla's habitat. It is a simple thing to do, but it can make a tremendous difference.
As told to Tim Barlass.