The long-finned pilot whale that died on Whanganui's South Beach last week was too weak to swim when refloating was attempted.
The whale was discovered on South Beach heading towards Whangaehu around midday last Thursday and died at 8.33pm that day.
Wildbase at Massey University performed a necropsy to determine the cause of death, with the Department of Conservation suspecting the pilot whale was an old individual.
"The whale had very worn teeth and some were missing," senior biodiversity ranger Sara Treadgold said.
"No squid beaks were found in its stomach, so it had not been fed for a while.
"The animal was underweight but had no sign of injuries or medical conditions."
Project Jonah general manager Daren Grover said female pilot whales tend to live around 60 years and males 30-45 years.
The whale was stranded alive and seemed lethargic and did not want to swim away when it could at high tide, Treadgold said.
The whale was not euthanised; it died after struggling to swim.
DoC staff were at the beach on Thursday evening and throughout Friday. They attempted to move the carcass out of the surf zone, but anchored it instead on the falling tide.
Chris Shenton, an iwi representative from Ngāti Apa Ngā Wairiki, was on site and supported with a karakia.
A contractor was employed to dig a burial trench and the animal was buried at South Beach.