A New Zealand environmental activist says fishing boats off the coast of Canterbury are sneaking into a mammal sanctuary at night and fishing illegally.
A team led by Earthrace New Zealand's Pete Bethune conducted covert surveillance in planes, boats and kayaks around the Banks Peninsula marine mammal sanctuary earlier this month.
Mr Bethune says his team witnessed a number of boats entering the sanctuary and fishing at night.
"At night, we've got boats sneaking inside the boundaries where they're not supposed to be, and we saw these vessels on multiple nights coming inside the zones where they shouldn't be fishing.
"I just think the marine mammal sanctuary there is a joke."
He says gill-net fishing boats working near the sanctuary were attracting the Hectors dolphins.
"We saw these boats fishing and Hectors dolphins playing around these boats and chasing food, and there's no doubt they're getting caught in those.
"I don't reckon it's a sanctuary at all - it's a killing field."
Mr Bethune says it's well documented around the world that gill net fishing is the number one killer of dolphins.
He said photos and data of the boats have been given to the Ministry for Primary Industries for investigation.