“Across the Waves: How Saltwater Crocodiles Conquered the Indian Ocean and Reached the Seychelles”

 

A remarkable new genetic study has rewritten a long-standing story about the ancient distribution of one of the world’s most powerful reptile species. Saltwater crocodiles (Crocodylus porosus) — best known today from the coasts of South and Southeast Asia, northern Australia, and the Pacific — once crossed thousands of miles of open ocean to inhabit the remote Seychelles Islands in the western Indian Ocean. This colonization occurred long before humans arrived and ultimately drove the island population to extinction.

Uncovering an Ancient Journey

Historical accounts from early European expeditions more than 250 years ago describe crocodiles as widespread along the Seychelles’ coastal shores. However, when permanent human settlement began around 1770, these crocodiles were hunted relentlessly and were gone within about 50 years.

For decades scientists debated whether these vanished crocodiles belonged to a unique island species or were simply members of a known crocodile group. A recent genetic analysis published in Royal Society Open Science has now resolved that mystery. By extracting and comparing DNA from museum specimens of the Seychelles crocodiles with samples from living populations, researchers demonstrated that the disappeared reptiles were saltwater crocodiles — not a distinct local species.

How They Made the Crossing

Saltwater crocodiles are uniquely adapted among large reptiles to long periods at sea. They possess specialized salt-expelling glands that allow them to tolerate salty ocean water, and their powerful bodies and muscular tails help them endure extended travel. These adaptations enabled certain individuals to drift or swim across vast distances, possibly carried by prevailing currents, to reach distant islands like the Seychelles.

According to researchers, the founding members of the Seychelles’ crocodile population likely traveled at least 3,000 kilometers (about 1,860 miles) across the Indian Ocean, and their genetic connections to populations thousands of kilometers away in the Pacific suggest widespread movement across the Indo-Pacific region over geological time scales.

Population Connections Across Oceans

Genetic patterns from the study show that saltwater crocodile populations were historically interconnected across enormous distances. Before their extinction in the Seychelles, the species’ range may have extended more than 12,000 kilometers (about 7,500 miles) from western Pacific islands to the western Indian Ocean, making saltwater crocodiles one of the most widely distributed reptile species on Earth.

These findings also underscore the role of sea currents, animal physiology, and evolutionary resilience in shaping how species dispersed long before humans dominated marine travel or global maps were drawn.

Human Arrival and Extinction

The disappearance of the Seychelles’ crocodile population highlights a pattern seen on many island ecosystems: when humans colonize isolated habitats, long-established wildlife often cannot survive. The hunting pressures and habitat changes that followed European settlement in the Seychelles in the late 18th century quickly led to the complete eradication of these ancient ocean travelers.

Scientific and Conservation Significance

This discovery not only settles a historical question about Seychelles crocodiles but also demonstrates the power of ancient DNA techniques to reveal hidden chapters of species’ histories. It reinforces how environmental adaptation — including tolerance of saltwater and ocean currents — allowed saltwater crocodiles to expand their range far beyond continental shores.

As conservationists work to protect crocodile populations in their current habitats, understanding these deep evolutionary journeys reminds us of the remarkable capabilities of wildlife when left to navigate natural environments across vast distances.

Sources

• “Saltwater crocodiles crossed the Indian Ocean to reach the Seychelles — before humans arrived and wiped them out,” Live Science, Skyler Ware; based on research in Royal Society Open Science.
• “Saltwater crocodiles traveled thousands of miles across the Indian Ocean, genetic study suggests,” Phys.org.
• “Saltwater crocodiles once crossed an ocean to reach the Seychelles,” Earth.com.