Surprise! Japanese Sardines Astonish Scientists by Crossing the Pacific to the West Coast

By fisheries.noaa.gov.

Next generation genomic sequencing of Pacific sardine reveals not one, but two species of sardine in the California Current in 2022 and 2023.

When research scientist Gary Longo first saw the results of his genomic analysis of sardines, he thought he must have mixed up his samples.

Besides the Pacific sardines common on the West Coast, many of the fish appeared to be another species. “It was a total shock,” he said. Then he compared their genetic code to other known species. “That was the ‘aha moment’ when we realized we were looking at a second species of sardine.”

The analysis shows that of the 345 sardine samples collected during NOAA Fisheries’ 2021 and 2022 Coastal Pelagic Species Surveys, all of the fish in 2021 were Pacific sardines, but those collected in 2022 were a mix of Pacific sardines and Japanese sardines.

Examination of another 825 sardines collected the following year found the same result: many were Japanese sardines. Known only from the west side of the North Pacific Ocean near Asia, the Japanese species had not been documented on the West Coast before.

The scientists from NOAA Fisheries and other institutions reported the surprise appearance today in the journal Molecular Ecology. Both species look so similar that only genetic examination can tell them apart. The scientists took advantage of recent advances in genomic sequencing to examine data from millions of genetic markers and constructed full mitochondrial genomes for sardine to verify the identification. .

In 2022 and 2023, Japanese sardines were found from Washington State to southern California and were sometimes schooling together with Pacific sardines. The Japanese sardines were 1 to 3 years old, typical adult age classes for sardines.

Curious if the Japanese sardines had been missed in previous surveys, the researchers took advantage of the genetic resources archive at the Southwest Fisheries Science Center.

read more at fisheries.noaa.gov.