DNA filtered from sea water has revealed the presence of rare shark species roaming the ocean that were previously missed by scientists.

Tests performed by an international research team have revealed the previously hidden diversity of sharks around the New Caledonian archipelago in the south western Pacific.

Their findings, which included the presence of hammerhead and bull sharks, have important implications for the conservation of marine life in these threatened waters.

By testing samples of water collected from the region, the scientists detected six shark species that had previously been missed by nearly 3,000 dives and 400 baited video traps.

“We are talking about literally a few bottles of water,” Professor Stefano Mariani, a conservation geneticist at the University of Salford, told The Independent.

Together with an international team of scientists, Professor Mariani applied their straightforward technique to locate sharks long feared ot have been wiped out in the area due to human encroachment on their habitat.

The method makes use of water-borne DNA from substances including faeces, mucus and scraps of skin. Genetic material collected this way is known as environmental DNA, or eDNA.

Over the years, scientists have assembled a genetic library containing all 500 or so species of shark.

“It has been possible in the past few decades for scientists to sample all of them and get DNA references,” said Professor Mariani.

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Using these reference points to guide them, the research team was able to sift through the wealth of genetic information contained in their water samples and pick out the genetic signatures left behind by individual species.

“These are not unknown species of sharks that nobody had ever seen – we are talking about species of sharks that are known to science, but were no longer known to inhabit those areas,” said Professor Mariani.

While they were reassured that these sharks had not gone locally extinct, the scientists said their results emphasise the need to protect species that may be evading our best efforts to monitor them.

Sharks attack submarine during filming for Blue Planet II

Their results were published in the journal Science Advances.

Notable species identified in the new study included the great hammerhead, an impressive creature valued both culturally and economically.

Like many hammerhead sharks, this species has been overfished due to its particularly large fins, which are used in some Asian nations to make shark fin soup.

Another species threatened by humans that was discovered by the new eDNA analysis was the silky shark, which is also valued for its edible fins.

The scientists came across more common species as well. Their analysis showed that previously unrecorded bull sharks were present in the region – a notable discovery considering this species is one of the few known to pose any real threat to humans. The presence of these sharks therefore suggests another use for eDNA analysis that goes beyond conservation efforts.

“This could potentially also be an interesting method to test waters where people think there are no sharks – maybe there are some sharks so you need to be a bit careful when you enter the water,” said Professor Mariani.

The data collected from the team’s eDNA samples was not restricted to sharks. In fact, shark material made up a tiny fraction of the contents of the 22 water bottles collected on the research trips around New Caledonian reefs.

The scientists now intend to document the rest of the creatures found using their DNA analysis, and expand the scale of their studies by sampling larger volumes of water.

Professor Mariani said in the future this low-effort method of undertaking a marine census could be applied by ordinary citizens in order to build a global map of underwater diversity.