OIST's eDNA survey found 126 fish beyond their northern records, a seaweed grazer among them

A seawater DNA survey of Japan's whole coastline has detected 126 fish species further north than they had ever been recorded, scientists from the Okinawa Institute of Science and Technology (OIST) reported on October 26 in Diversity and Distributions. The list includes fish that fishers sell and at least one that is suspected of stripping seaweed beds.

OIST calls it the largest marine environmental DNA (eDNA) study in Japan and the first time the method has been applied at the scale of a whole country.

Buckets of seawater instead of nets

Environmental DNA works by sampling the tiny fragments of DNA that animals shed into the water. A single bucket of seawater can reveal which species have been nearby, which is far cheaper than dive surveys or trawling, though contamination has to be carefully controlled.

The team contributed nearly 1,000 new samples and combined them with earlier efforts. In total the dataset holds 2,672 samples taken at 316 locations between 2017 and 2024. From these, the researchers identified thousands of fish species before flagging the 126 that turned up north of their recorded ranges.

The release frames the results as evidence that these species "may" be living further north. A DNA trace shows a species was present in the water, not how many individuals live there or whether they breed.

Why it could only be done in Japan

First author Ayşe Haruka Oshima Açıkbaş, who has since completed her PhD at OIST, said Japan was one of the few places where a survey like this was possible. The reference tool used to match DNA to species, known as the MiFish primers, was developed in Japan, and local researchers have spent years sequencing the region's fish, which makes identifications more complete.

The other ingredient was people. The survey depended on a network of marine stations, fisheries and environmental agencies to collect water along the coast.

The fish that matter to the dinner table

Among the 126 species are commercially important fish such as Japanese scad and blacktip grouper. Also on the list is the black rabbitfish, a grazer suspected of causing lasting damage to seaweed beds in a phenomenon Japanese researchers call isoyake.

Senior author Timothy Ravasi said fishers are already noticing different catches than a few decades ago, and that the change hits small family fishing businesses hardest because new species need new gear, skills and buyers.

The team now wants to move from mapping where DNA appears to modelling why a species' DNA appears at certain sites but is absent from others, which would let the data be used for forecasting rather than just snapshots.