The pup was born in the shallows of St Kilda Beach in Dunedin yesterday morning.
The Department of Conservation said in a statement the pup was euthanised after its mother failed to bond and left for the ocean this morning.
Born to what was thought to be a first-time mother, the pup would likely have drowned shortly after birth had it not been taken from the water and placed near the mother by a member of the public.
It was hoped the mother and pup would bond, however by nightfall there was no sign this had happened, and the pup hadn’t been fed, Doc said in the statement.
This morning the mother left the pup, which was very weak and unresponsive.
After being assessed by a vet and Doc staff member as being unable to feed even if the mother returned, the decision was made to euthanise it.
"Although it was a sad end for the pup, it was a great example of the whole community doing what they could to give the pup the best chance," Doc Ranger Jim Fyfe said
The Dunedin City Council and its contractors limited vehicle and public access to the mother and pup, while members of the public and NZ Sea Lion Trust volunteers kept a watchful eye over it and alerted dog-walkers and passers-by to its presence.
"It was great to see so many people interested in this incredibly rare event, and sad for all involved that the outcome couldn’t have been better.
“While we are lucky to have such special visitors to our coastline, people should also be mindful and respectful that leopard seals are large wild animals that should be viewed from at least 20 metres away at all times," Mr Fyfe said.
Dr Krista Hupman of NIWA, along with a team of researchers at leopardseal.org is studying leopard seals around New Zealand and flew down from Wellington to offer her support and advice.
"The opportunity to witness this incredibly rare event was too good to miss, as this is only the second time ever, and the first time in 40 years, that a leopard seal has given birth on New Zealand shores."
A spokesperson for Leopard Seal Sightings New Zealand said in a statement it was a "terribly emotional time" for everyone involved,
"The mother left the pup alone this morning and returned to sea.
"Unfortunately the pups condition deteriorated so much the vet determined it would not be able to suckle even if the mother returned to the beach.
"Due to this the Department of Conservation decided it was best to euthanise the pup in an effort not to prolong any suffering."
Doc would work with local iwi to decide the next steps.
The public were asked to stay behind barriers at the beach in case the mother returned.
The spokesperson thanked Dunedin man Dalton Williams who saved the seal pup from drowning after it was abandoned by its mother after being born in the water.
