One of the iconic birds of the Galapagos Islands, the blue-footed booby, has suffered a sharp population decline, authorities in the Ecuadoran archipelago said Wednesday, blaming overfishing.

"We are extremely concerned about what is happening with this population," said Victor Carrion, director of the Galapagos National Park Ecosystems, located some 1,000 kilometers (600 miles) off the Ecuador coast.

A study published in the journal Avian Conservation and Ecology and partly funded by Galapagos authorities, found the blue-footed booby population had dropped from 20,000 in 1960 to just around 6,400 adults in 2012.

The study also found few adult pairs had babies between 2011-2013, and almost no young birds were observed during the study period.

The most likely cause of the decline was a scarcity of sardines, the main food source for the bird species, whose images adorn postcards of the archipelago, where Darwin conducted the studies that led him to the theory of evolution.

The sardines are disappearing because of "overfishing in northern Peru, from where the current carries" the fish to the Galapagos, Carrion said.

But he expressed confidence the decline could be reversed through protective measures to keep the bird species from being listed as endangered.