Scientists shocked by report that 'Japanese sardines discovered for the first time on the US West Coast'
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The National Oceanic and Atmospheric Administration (NOAA) Fisheries Service has reported the discovery of a previously unidentified 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 team initially set out to study the population genetic structure of the California sardine (Sardinops sagax), but in the process of analyzing the genome, they found unexpectedly strong genetic differentiation, and after further analysis, they discovered the existence of Japanese sardines.
NOAA's research team collected 345 individuals in 2021 and 2022. Of these, all 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, but no Japanese sardines were detected during this period. This suggests that the Japanese sardines' crossing of the Pacific Ocean may have occurred around 2022.
The Japanese sardines found were 1 to 3 years old, with 2-year-old fish predominating. Their distribution range is wide, stretching from Washington state to Southern California, and they have sometimes been spotted forming schools together with California sardines.
Although Japanese sardines and California sardines look almost identical, NOAA's research team used the latest genome sequencing technology to confirm that the two species are genetically distinct, using millions of genetic markers and the complete sequence of the mitochondrial genome. According to the research team, it is estimated that Japanese sardines and California sardines diverged about 200,000 to 300,000 years ago. This period overlapped with the ice age, and it is believed that the cooling of the North Pacific Ocean geographically isolated the two species and promoted speciation.
By Brian Gratwicke
The research team suggests that the reason Japanese sardines have become present in the California Current ecosystem may be that unusual marine heatwaves observed in the North Pacific over the past decade have created a corridor with favorable environmental conditions that allows Japanese sardines to migrate.
As for future issues, the research team stated that many questions remain, such as the possibility of interbreeding between the two species, their impact on the ecosystem, and whether Japanese sardines will persist in this new habitat. They also argued that this discovery is an important example for understanding the impact of climate change on marine ecosystems and shows the importance of long-term monitoring.
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