Grover said there was a mass stranding of several hundred of the whales in 2017.
A post on the charity's Facebook page alerted its volunteers to the whale washing up on Waimari Beach on Thursday.
"Fetal folds are still visible meaning the animal is most likely less than 6 months old. The calf looked to be in a relatively healthy physical condition with no obvious scars and injuries."
The young long-finned pilot whale. Photo / Rebecca Williams
The Department of Conservation and Ngāi Tahu are on site preparing for a burial, the post said.
Grover said anyone who comes across a beached whale, dead or alive, should contact the Department of Conservation immediately.
"The people that came across this whale were very, very clever. They had to leave but left a note saying 'DOC has been contacted' which meant other people who saw it wouldn't panic."
He said this is a reminder to the public to keep watch for whales.
"In summer, we get species migrating or coming close to the shore. We get many different species here in New Zealand.
"If you see one, don't panic, reach out and ask for help."
• Contact DOC on 0800 362468 or Project Jonah on 0800 494253 if you come across a whale.
