This is the heartbreaking moment a pregnant shark was found dead after being strangled by a tourist's discarded hat.

The dead blacktip reef shark had the circular band of the wide-rimmed straw sun hat wrapped around its neck when it was seen lying on a coral reef around the Phi Phi Islands in Krabi province off the coast of southern Thailand.

Divers who noticed the endangered marine creature on February 9 recorded the creature as they carefully removed the item of ocean pollution.

Footages shows how the shark was already in a state of decomposition and that three stillborn babies had fallen from the mother shark's womb.

Hat Noppharatthara Mu Koh Phi Phi National Park is now investigating the incident after retrieving the mother shark and her babies underwater while warning locals and tourists about keeping the oceans clean.

A national park spokesman said: 'Initial investigations showed that the shark swam through the hat and parts of it wrapped into the reef. It was unable to swim further upon being caught and died by suffocation.'

The blacktip shark is listed as ‘near threatened’ by the International Union for Conservation of Nature (IUCN) due to its declining population but it is not yet listed as a protected species in Thailand. One of their biggest threats come from being hunted by fishermen for their fins and meat, particularly in China where Chinese men regard it as a delicacy that boosts men's libido.

These sharks can be found along coastlines nearly everywhere in Thailand but the best places to spot them are in the Phi Phi Islands or the Similan Islands. They are known for their timid demeanour as they often flee from humans except if being handed food.