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Hawaii's Kona Coast is home to the most accessible population of manta rays in the world.

Night time boat tours are hugely popular - tour operators say up to 300-400 people try to see the rays each night.

But while many operators are responsible, there are concerns that not everyone is abiding by the rules.

State authorities are drawing up new rules to limit visiting divers - there is talk of a permit system and a requirement for boats to operate in shifts.

The Travel Show's Carmen Roberts reports.