Marine scientists working at nearby Portobello would have liked to keep it and study it, but that was not practical, New Zealand Marine Studies Centre programme director Sally Carson said last night.
"It probably weighs over a tonne and getting it off the beach would probably require a boat.
"We have limited resources on a Friday night and limited space in our freezers and there is no-one actually researching sunfish at the moment, so we will probably leave it to the elements.
"It will break up and get eaten quite quickly."
The sunfish, which washed up between Company Bay and Broad Bay yesterday, had created much interest, Ms Carson said.
The marine studies centre fielded "millions" of telephone calls about the sunfish.
She found it was "very cool to see" and feel.
Ocean sunfish
•The heaviest known bony fish in the world.
•Can reach 3.3m in length and weigh up to 2.3 tonnes.
•Average adult fish 1.8m long and weighs one tonne.
•Native to tropical and temperate waters.
•Usually stays in water warmer than 10degC
• Mainly eats jellyfish but also eats squid, small fish and fish larvae
•Can swim as deep as 600m and spends a large portion of its life at depths greater than 200m
•Is so named because it turns on its side and sunbathes on the surface of the ocean
•Is often killed by parasitic infestations. Also eaten by orcas and sharks.
