A 4.5 tonne sperm whale that washed ashore in southern Spain died from ingesting large amounts of plastic sheets used in greenhouses on farms in the region, a scientist revealed.

The whale, washed up last year on a beach in Andalusia, had over 17kg of garbage blocking its stomach, including 30 square metres of plastic sheeting, said Renaud de Stephanis, a marine biologist at the Donana Biological Station, run by the Spanish National Research Council.

"We quickly realised that it had a real greenhouse inside its stomach. We did not expect it, but it did not surprise us," he said.

"There were a dozen metres of plastic rope, plastic sheeting used on the outside of greenhouses, and plastic sheeting used inside, and even two flower pots."

More than 250 marine animals including turtles, dolphins and otters have problems because of plastic garbage that finds its way into the ocean and which can cause them to choke, de Stephanis said.

Sperm whales, which can be found throughout the Mediterranean Sea, typically feed on large squid which could resemble drifting plastic sheet. Sea turtles, which feed on jellyfish, often choke on plastic bags.

The whale that washed ashore in March last year on a beach south of Granada, not far from Almeria, was "in a state of advanced emaciation", said de Stephanis. "It was as if it had a rock inside its intestine. Nothing could get through. There was so much plastic that it finally exploded," he added.

Very few large mammals, including only four sperm whales, have been proved to have died because they swallowed plastic waste, de Stephanis said.

The discovery shows that "the sea is full of rubbish" and that waste management systems for plastic, not only in Spain, are not always effective, he said.

"These big plastics crumble and the little pieces also go inside fish. And that is what we end up eating," said de Stephanis.