The huge, 36-stone leatherback turtle that was rescued in a Spanish port over the weekend has died shortly after being released to sea.

The marine animal turned up at the Port of Mazarron in the Spanish region of Murcia on Saturday with injuries to its flippers and shell after becoming entangled in a fishing net and struck by vessels.

The leatherback turtle (Dermochelys coriacea), which weighed a whopping 230 kilogrammes (36 stone), was almost 1.5 metres (4 feet and 11 inches) in length.

The turtle was treated at L’Oceanografic, an oceanarium in the Spanish city of Valencia.

The oceanarium said in a statement on 21st March: “Aquarium professionals carried out the relevant veterinary procedures, physical examinations, ultrasound, blood tests, etc., and healed the multiple lesions and erosions that it had all over its body.

“Although its initial condition was very weak, the animal is responding favourably to treatment and will be returned to the sea today (21st March) in Cartagena.

“For this reason, a satellite device has been installed on the turtle’s shell, which will provide scientists with a great deal of information about the routes and behaviour of these fascinating animals at sea.”

However, shortly after being released off the coast of Cartagena on Monday, the huge turtle died.

Carers said the turtle had shown signs of responding well to the treatment over the weekend and believed it was ready to return to its natural habitat. However, the marine animal did not react to contact with the water as expected and submerged and died.

They recovered the turtle’s body and will carry out an autopsy to establish the exact cause of death.

Leatherback turtles are listed as ‘critically endangered’ on the IUCN’s Red List and Spain also includes it in its List of Wildlife Species under Special Protection.

The oceanarium said: “The leatherback turtle is one of the largest turtle species on the planet, weighing up to 600 kilos, and many aspects of its biology are still unknown.

“Its main threats are the hunting of adult specimens on the beach, accidental death in fishing gear, and the plundering of their nests.

“It is characterised by an extraordinary ability to regulate its temperature, which allows it to tolerate very low temperatures and dive to great depths.”

The Spanish park, one of the largest aquariums in Europe, has received nearly 24 million visitors since 2003.