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.

The whale shark appeared emaciated and it seemed likely that the line had been interfering with its ability to feed.

The family were unaware of the previous sightings but after consideration decided to take matters into their own hands.

They were initially worried about scaring the whale shark off and daunted by the thickness of the braided line, later reckoned to be 12cm and to weigh some 70kg.

It took Rohrer five breath-hold dives over the space of about 45 minutes to saw through the line with a 10cm dive-knife.

"That's a good example of how the things that we discard can destroy beautiful animals like that so easily," Rohrer later told Hawaii News Now.

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