Forest and Bird is worried at a spike in the number of dolphins being accidentally caught in fishing nets off Bay off Plenty.

There were 44 reports of dolphin bycatch over the last year.

In all of the six years prior, the recorded number was only nine.

Forest and Bird's Dr Rebecca Stirnemann says it's a massive increase.

She believes it's likely there are more incidents which go unreported.

"We're relying on fishing boats reporting these and not all of them do. So we don't know the full extent of the problem"