The past month, Lanky was hesitant to bear weight on his legs and began to refuse food and medication, he said.
"The welfare of our animals is paramount, and the observations showed we were no longer able to sustain his quality of life, so the decision to euthanise Lanky was made in his best interests."
Lanky arrived from Adelaide Zoo in the capital in 1978, Mr Basson said.
"Zoo staff are particularly sad to see Lanky go, as he has been a real character and much loved by everyone who has cared for him over the past decades."
Wellington Zoo's senior keeper, Phil Wisker, who cared for the pelican for nine years, said the bird was a popular attraction for visitors.
"So many of our visitors have told us about their fondness for Lanky, and it's been amazing to see them connect with this very special bird."
He ate a kilo of fish everyday and his favourite food was kahawai, he said.
"However, he was definitely seen from time to time sneaking food off his neighbours, the capuchin monkeys and spider monkeys, who may not have appreciated his behaviour."
Pelicans
* An Australian pelican has the longest beak of any bird in the world.
* The species is commonly found throughout Australia.
* New Zealand had a native pelican which died out before human colonisation, which is believed to have been a sub-species of the Australian pelican.
* Another Wellington Zoo pelican, Percy, lived until age 62 and made it into the Guinness Book of Records as one of the world's longest living birds.