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Scientists have taken an unprecedented look at marine fish species living in the world's oceans by studying traces of genetic material in seawater. One of the most surprising results was discovering species in places where records say they are missing.

The problem with current mapping projects, which aim to chart where species live and the conditions they need to survive, is that they are based on limited information. Traditional methods such as nets and underwater cameras primarily target easy-to-reach areas and often miss small, elusive species. This means our picture of ocean biodiversity is far from complete.

A powerful tool for global surveys

To fill these knowledge gaps, research led by Loïc Sanchez at the University of Montpellier, France, and the Center National de la Recherche Scientifique used a powerful technique called Environmental DNA (eDNA). This approach can detect multiple species and identify their ranges without capturing or photographing them.

The research team collected nearly 1,000 water samples from 542 locations worldwide, including polar regions and tropical islands. They then analyzed the fish DNA in those samples and compared it with occurrence databases, such as the Global Biodiversity Information Facility (GBIF).

These new eDNA surveys reveal just how incomplete our records are. According to results by the team in PLOS Biology, 93% of geographic ranges were underestimated. This means species were living far outside the areas where they were historically mapped. For example, the crocodile icefish, which was previously known only to live in the freezing conditions of the Antarctic region, was detected in Patagonia (southern South America).

Additionally, 7% of species' ecological niches were also underestimated, meaning they were found to tolerate environmental conditions that were previously thought impossible for them to live. For example, the crocodile icefish was found in water nearly 10 degrees Celsius warmer than the maximum temperature at which it was known to survive.

Solving blind spots

The clear implication of these findings is that current mapping methods need to be updated, as they leave vast blind spots.

As the scientists commented in their study, "Our results suggest that sampling in remote areas and performing eDNA surveys in over-sampled areas may both increase fish ecological niche ranges toward unexpected values with consequences in biodiversity modeling, management, and conservation."

If conservation efforts are to have a better chance of protecting species from threats like climate change and human activity, their entire habitat range and survival limits must be known to assess whether they're at risk of extinction.