Updated 5:05pm: More than a dozen common dolphins have died following a mass stranding on the Cavalli Islands in the Far North.

Massey University scientists have been working alongside DoC since the discovery was made yesterday.

DoC Bay of Islands Conservation services manager Rolien Elliot says a yachtie had reported a dolphin in the shallows off Motukawanui Island.

"When that was responded to we went round the corner to Wai-iti Bay and there were more dolphins on the beach there.

"Unfortunately they had passed away so they were carcasses on the beach."

Ms Elliot says it's unusual for common dolphins to become stranded and the cause is yet to be known.

DoC Bay of Islands Conservation services manager Rolien Elliot says the cause is yet to be discovered.

"We've had Massey University scientists with us and they took samples of all the carcasses and yes, that will help them towards research into this issue."