In which year did the hippo population reach 30 in number?

In May 2006, the hippo was identified as a vulnerable species on the IUCN Red List drawn up by the International Union for Conservation of Nature (IUCN), with an estimated population of between 125,000 and 150,000 hippos, a decline of between 7% and 20% since the IUCN's 1996 study.