Ecuador seized 211 shark fins in the Galapagos Islands in its second capture in the past month of illegal "finning" that environmentalists say is threatening the ecosystem, according to the park.

Galapagos National Park hauled in an Ecuadorian cargo ship on Wednesday near San Cristobal island that was carrying the fins and detained its crew, a park official told Reuters.

It is the second shipment caught in the past month in the islands, which are located 1,000 kilometres west of mainland Ecuador in the Pacific Ocean.

Last month, the park seized 815 fins, which are sold to make a costly soup in Asia.

Conservationists worry that shark "finning" could cut down on Galapagos' top marine predators.

The islands are famous for their tortoises and exotic birds that inspired 19th century British naturalist Charles Darwin's theory of natural selection.