Sharks driven away by illegal fishermen from a remote reef off Western Australia's northern coast have started to return, thanks to a crackdown by Border Force officers.

Scientists, who say the animals are essential to the health of coral reefs, believe this is a globally significant lesson in preserving fragile ecosystems.

Key points: Sharks return to Ashmore Reef, 350km off the Kimberley coast in northern WA

Sharks return to Ashmore Reef, 350km off the Kimberley coast in northern WA Scientists from the Australian Institute of Marine Science embarked on a research project at the reef in 2004

Scientists from the Australian Institute of Marine Science embarked on a research project at the reef in 2004 Border Force deployed patrol boats near Ashmore Reef to enforce a total fishing ban in 2008

Border Force deployed patrol boats near Ashmore Reef to enforce a total fishing ban in 2008 According to Maritime Border Command, 260 vessels were detected between about 2004 to 2007

According to Maritime Border Command, 260 vessels were detected between about 2004 to 2007 Last financial year, 15 vessels were detected in Australian waters, of which three were in Western Australia

Ashmore Reef, an atoll 350 kilometres off the Kimberley coast near Australia's border with Indonesia, is home to an array of marine life.

It is also a target for illegal fishermen from South-East Asia.

High on their hit list are sharks whose fins and flesh are highly valued in many Asian countries.

In 2004, concerned by a spike in foreign vessel incursions into Australia's northern waters, scientists from the Australian Institute of Marine Science embarked on a research project at the reef.

Marine ecologist Conrad Speed and his colleagues, working in collaboration with the Global FinPrint Project, set up a series of underwater cameras to capture fish stocks.

"There was some concern that the number of fishing vessels were increasing in the area, so to get an understanding of what the fish and shark stocks look like in the area, we started using baited cameras to get an initial assessment," Dr Speed said.

Illegal fishing a threat to biodiversity

What they saw was concerning, with many sharks normally found at healthy reefs absent.

Australian Border Force wase also worried about the increase in illegal vessels to the region.

Scientists conduct research on shark populations at Ashmore Reef in northern WA. ( Supplied: Global FinPrint Project )

Commander, Maritime Border Command Peter Laver is in charge of protecting Australia's maritime borders, and believes illegal fishing is a significant threat to Australia's biodiversity.

"Illegal fishing creates unsustainable pressure on our marine environment. It reduces biodiversity, meaning that fish stocks become unsustainable over time," he said.

In 2008, as part of an increased effort to reduce the hundreds of boats coming into Australian waters, Border Force deployed patrol boats permanently in the vicinity of Ashmore Reef to enforce a total fishing ban.

"It's our remit and responsibility to protect those important resources for Australia and indeed the biodiversity within the ocean area to ensure that sustainable fishing practices maintain a viable marine environment," Commander Laver said.

According to Maritime Border Command, 260 vessels were detected between about 2004 to 2007.

Last financial year, 15 vessels were detected in Australian waters, of which three were in Western Australia.

This year, seven vessels have been detected. The most recent was an illegal fishing vessel intercepted off the Kimberley coast in February.

"The current incursion [rate] is very low because of the compliance activity and our presence throughout the region," Commander Laver said.

Species never seen on reef before are documented

Ashmore Reef in northern Western Australia where scientists are conducting research on shark populations. ( Supplied: Glabal FinPrint Project )

After returning to Ashmore Reef in 2016, Dr Speed said the impact had been huge.

"Over the last eight years we've seen a dramatic increase in the number of sharks," he said.

"In fact, I think we've seen four-and-a-half times as many sharks as we did back in 2008, and it most likely has been due to this reduction in illegal fishing."

Scientists documented species they had never seen before including nurse sharks, leopard sharks, rays and wedge fish.

Dr Speed said the rigorous approach to illegal fishing at Ashmore Reef could help guide management practices at reef systems around the world.

"This is one of the few stories that we know of where shark populations have increased through the protection of the marine protected area," he said.