A post-mortem examination continues today to determine the cause of death of Moko the fun-loving dolphin, but an international expert on the species says it may never be known what killed him.

Wade Doak said Moko's body appears to be too decomposed to definitively say what killed him, but if he had been struck by a boat propeller it would be obvious.

He said, however, that a likely cause of death would be drowning from set nets and he has urged New Zealand lawmakers to ban them.

"Moko left behind such a rich heritage," he said.

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