A rising population of feral animals and invasive plants on Astola, Pakistan’s only marine protected island, is posing a growing threat to its rich but fragile biodiversity, with some rare seabird species almost eliminated.

Located in the northern part of the Arabian Sea, east of Pasni district in the southwestern Balochistan province, Astola is the country’s largest offshore island and the only marine protected area known for its rich marine biodiversity.

The island is one of the world’s largest breeding sites of the yellow-billed tern, a small seabird found in Latin America, apart from supporting a large variety of water birds such as coursers, gulls, and plovers.

Its glistening beaches are also nesting grounds for the endangered green turtle and hawksbill turtle, while the Astola saw-scaled viper, a subspecies of the Russell’s viper is endemic to this small island.

However, a gradual increase in the number of stray cats, as well as rats, has resulted in a rapid decline in the population of turtles and seabirds in recent years. They are attacking and killing nesting seabirds, while also damaging and eating their eggs.

Astola is known to be the world’s largest breeding colony of the yellow-billed tern, but cats have now eliminated the bird from the island. Many seabirds, especially terns, used to make thousands of nests on isolated rocky platforms and ledges across the island. However, this is no longer the case as these feral animals have wreaked havoc on the island’s already fragile biodiversity.”

‘Ferocious hunters’

Cats are not part of the natural fauna of Astola and were actually brought there by local fishermen to hunt rats. According to Khan, a local fisherman released a pair of cats on the island in the 1970s to control rat population, which was feasting on seabirds and migratory quails. The rats would attack seabirds’ nests, while also damaging fishing nets and other equipment laid out by sailors.

Rather than protecting the nests and fishing nets, these cats have turned out to be a permanent nemesis. They are nocturnal and ferocious hunters who have become the top predators of the island, adding that they even feed on reptiles, including skinks and agamas. “Astola, which was once a crowded bird colony, is deserted today. The few birds that still nest here are careful to do so on the detached rocks off the island’s southern shore.

‘Difficult to control’

As part of efforts to protect the island’s biodiversity, WWF-Pakistan launched a program to exterminate the cats in 2012, culling at least 18 adult cats. However, the current number on the island is estimated to be more than 50. Their population is difficult to control because of their nocturnal habits and the island’s treacherous terrain, which makes it extremely difficult to track them down.

Invasive plants like mesquite are also spreading rapidly on the island, covering a part of its southern section and smothering other plant species.