Kanehoalani Kawelo spotted the whale shark at a depth of 10-12m while snorkelling off the island of Lanai on 29 July, and could see that the tightly wrapped line was digging into its fins.

He and his sister were with their mother Kapua Kawelo and husband Joby Rohrer, both marine biologists.

The entangled animal had been spotted in other Hawaiian locations in previous weeks and an alert had been issued by the US National Oceanic & Atmospheric Administration for sightings to be reported so that official action could be taken.