A chance discovery during routine research has revealed that Japanese sardines, previously thought to live only in the Asian North Pacific, have crossed into the American Pacific off the U.S. West Coast.
“It was a total shock,” NOAA research scientist Gary Longo said of the finding.
In a paper published 23 October in the journal Molecular Ecology, researchers suggested that climate change may be responsible for the fish's appearance.
“Small coastal pelagic fish such as sardines are good indicators of change," Longo said. "Often, they are the first ones we see responding to shifting temperatures because they have short generation times, are highly mobile, and can use a variety of habitats.”
NOAA's annual survey of coastal pelagic species led to the surprise discovery of Japanese sardines in U.S. waters from Washington to Southern California, where only Pacific sardines were thought to reside. The two species are indistinguishable to the naked eye, but genomic analysis confirmed their differences. Scientists reviewed surveys dating back to 2013 to determine the date the Pacific crossings began and found that Japanese sardines had only entered the West Coast samples starting in 2022.
The study’s authors have suggested that marine heatwaves warming the North Pacific in the last decade may have opened a new habitat to the Japanese sardines. Climate change is likely to blame for shifting stocks in many worldwide fisheries, with coldwater species moving and disappearing and warmwater species extending their ranges northward.
“It leaves us with many more questions than we can possibly answer right away,” Southwest Fisheries Science Center Researcher Matthew Craig, who was also a co-author of the study, said. “A lot of fish distributions change as ocean conditions change. Now, the question is whether Japanese sardines will die out over time, or will they persist in this new part of their range?”
Another key question the scientists hope to answer is whether the two sardine species can interbreed. Since Pacific sardine stocks have diminished in the California Current, the answer to this question would inform how sardine populations are managed in the West Coast fisheries.
Southwest Fisheries Science Center Director Kirsten Koch pointed out that the finding underscores the importance of long-term monitoring like the species surveys that NOAA conducts.
“This is one of those remarkable discoveries that never would have happened if scientists had not been out there, looking," Koch said. "The long-term records from earlier surveys also help us understand how unusual it is.”
