Scientists are shocked by the report that “Japanese sardines were discovered for the first time on the West Coast of the United States” – GIGAZINE

by Simona Scolari

National Oceanic and Atmospheric Administration(NOAA) The Fisheries Service has reported the discovery of the previously unknown Japanese sardine (Sardinops melanosticta) in the California Current ecosystem along the west coast of the United States.

Molecular Ecology | Molecular Genetics Journal | Wiley Online Library
https://onlinelibrary.wiley.com/doi/10.1111/mec.17561

“A Total Shock” – Japanese Sardines Detected in US Waters
https://scitechdaily.com/a-total-shock-japanese-sardines-detected-in-us-waters/

NOAA researcher Gary Lango and his colleagues initially began their research to investigate the population genetic structure of the California sardine (Sardinops sagax). However, in the process of genome analysis, unexpected strong genetic differentiation was found, and detailed analysis revealed the existence of Japanese sardines.

NOAA research teams collected 345 individuals in 2021 and 2022. Of these, all of the samples collected in 2021 were California sardines, but 50 of the samples collected in 2022 were found to be Japanese sardines. Furthermore, in the 2023 survey, 334 individuals, or approximately 40% of the 825 samples collected, were identified as Japanese sardines.

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The research team also analyzed past survey samples from 2013 to 2021, and no Japanese sardines were detected during this period. This suggests that the crossing of the Pacific Ocean by Japanese sardines may be a phenomenon that occurred around 2022.

The Japanese sardines discovered were between 1 and 3 years old, with 2-year-old fish predominating. Its distribution range is wide, from Washington state to Southern California, and it has been confirmed that it sometimes forms flocks with the California sardine.

Japanese sardines and California sardines look almost identical, but NOAA researchers used the latest genome sequencing technology to determine whether the two species are genetically distinct, using millions of genetic markers and the complete sequence of their mitochondrial genomes. We have confirmed that they are different species. According to the research team, it is estimated that Japanese sardines and California sardines differentiated about 200,000 to 300,000 years ago. This period coincided with the Ice Age, and the cooling of the North Pacific is thought to have geographically isolated the two species and promoted speciation.

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The research team believes that the reason why Japanese sardines are now found in the California Current ecosystem is due to the effects of unusual marine heatwaves observed in the North Pacific over the past decade, allowing Japanese sardines to migrate. This suggests that a corridor with favorable environmental conditions may have been formed.

Looking ahead, the research team says many questions remain, including the potential for interbreeding between the two species, the impact on the ecosystem, and whether Japanese sardines will persist in this new habitat. He also argued that this discovery is an important example for understanding the impact of climate change on marine ecosystems, and also demonstrates the importance of long-term monitoring.