QUITO, May 2 (Reuters) - Ecuador should step up efforts to protect the unique ecosystem of the world-famous Galapagos islands from growing tourism and immigration, a United Nations envoy said on Wednesday.

"It is crucial for us to eliminate these threats to secure the conservation of biodiversity ... The government has to show its efforts to confront those threats," UNESCO Director-General Koichiro Matsuura said during a visit to Quito.

President Rafael Correa declared the pristine islands at risk in April and said Ecuador would consider suspending some tourism permits. More than 145,000 people visited the islands last year.

The volcanic archipelago, located 625 miles (1,000 km) west of Ecuador's coast, inspired British naturalist Charles Darwin's theory of evolution.

A growing population, illegal fishing of sharks and sea cucumbers, and internal bickering among the islands authorities have taken a toll.

Centenarian tortoises and blue-footed boobies live alongside 24,000 islanders who earn a living from fishing and a growing tourism industry.

Thousands of mainland workers have also flocked to the islands in recent years, seeking better paying jobs. The government plans to enforce stricter immigration control.

UNESCO could decide in June if the World Heritage site should be declared "in danger."

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