Researchers find evidence of different sardine species off West Coast

Gary Longo was looking for what he thought would be small genetic differences across a single species of small, ocean-dwelling fish: Pacific sardine.

But as he examined the early data, he suddenly got a sinking feeling. He was looking at what appeared to be two completely different species.

Pacific sardines are small but ecologically important fish. For fishery management purposes, they are usually grouped into three subpopulations: the northern stock, the southern stock and the Gulf of California stock.

Longo, a contractor with the National Oceanic and Atmospheric Administration’s Southwest Fisheries Science Center, was part of a group looking to see if the different sardine stocks were genetically distinct from each other.

Now, as he looked at the data, he thought he must have made a mistake. Maybe he’d accidentally swapped plates with different samples.

Gradually, he and Matt Craig, a research geneticist with the center, realized they were looking at a sardine, but a species of sardine they had never detected along the West Coast of North America before: Japanese sardine, thousands of miles away from home.

In a paper published Wednesday, Craig and Longo theorize that unusually warm waters in the North Pacific Ocean may have created a sort of bridge, allowing Japanese sardines to overwinter there, moving from their usual habitat in the West Pacific over to the East Pacific. Craig and Longo’s work indicates Japanese sardines were present off the West Coast of North America in 2022 and 2023.

To the researchers, it’s another chapter in the story of how shifting ocean conditions are rapidly reshuffling species. In the last few years, market squid temporarily shifted north. Atlantic bluefin tuna appeared in fisheries hundreds of miles north of their usual summer feeding grounds. And now: sardines.

For researchers and fishery managers there are more questions than answers, but the discovery could complicate efforts to understand the Pacific sardine population off the West Coast at a key moment.

Unknown impacts

NOAA is in the middle of attempting to develop a plan to rebuild that species following years of dramatic decline and amid litigation over the agency’s response. The West Coast population of Pacific sardines, the northern stock, were declared overfished in 2019. There hasn’t been a fishery on them in nearly a decade.

A court rejected NOAA’s rebuilding plan earlier this year, agreeing with environmental groups that NOAA did not properly execute a plan to rebuild the Pacific sardine population and prevent overfishing by the legal deadline. A new rebuilding plan will need to be in place by June.

Michael Milstein, a spokesman for NOAA, says there isn’t enough information yet to say what the Japanese sardines could mean for fishery management. NOAA just completed its California Current Coastal Pelagic Species Survey, a trawl survey that travels from Canada to Northern Baja Mexico each summer.

“That will tell us more about how many are out there now and whether there is a continuing trend,” Milstein wrote in an email to KMUN.

Pacific sardines and Japanese sardines so closely resemble each other that it is nearly impossible to tell them apart just by looking at them. As researchers collected fish and took tissue samples, there was nothing they could see to indicate they were holding different species in their hands – until they looked at things on the much smaller level of DNA.

Evidence in Japanese sardine’s DNA suggests they’ve been here before, sharing a relatively recent evolutionary past with Pacific sardines. “Relatively recent” means tens of thousands of years ago, though. Large scale climate changes likely separated the two groups, Craig said. Their DNA is now distinct from each other.

Today, Pacific sardines and Japanese sardines live on opposite sides of the Pacific Ocean with the cold waters of the Northern Pacific forming what researchers had previously believed was an impassable barrier for migration in the modern era. They form an important base to the food chain as fodder for larger animals that humans like to eat.

More questions

Longo said sardines are a helpful species to study if you want to understand shifts in ocean temperatures. They are a highly mobile fish, both as adults and when they are larvae. They are generalists, able to live in a wide range of habitats.

“They tend to follow changing temperatures pretty well and quickly,” Longo said. “So they can kind of be thought of as a canary in the coal mine for temperature shifts — and there may be more coming if this habitat corridor stays open and is ecologically OK for other species.”

For Longo and Craig one of the biggest questions they have — besides the obvious question of whether the Japanese sardines are here to stay — is if Japanese and Pacific sardines will hybridize. That is, interbreed and produce viable offspring.

According to Longo, such hybrids could be detected at the genetic level.

In fish, Craig says they do see quite a few instances of hybridization.

“So if that’s the case going on here, that’s just going to add a whole other layer to the onion we’re trying to peel back — and give us more questions,” he said.

If the two sardine species aren’t able to interbreed and the Japanese sardines stick around, they could end up competing with Pacific sardines for resources

Given the similarities between Pacific and Japanese sardines Craig says there are likely plusses and minuses to them sharing space in the same part of the ocean.

“What does it mean for the fish over here? What does it mean that the Japanese sardine are here? The real answer to that is we don’t know yet,” Craig said.

But, he added, that’s science at its most fun: When you stumble across something that leaves you with more questions than answers.

This story comes to you from the Northwest News Network, a collaboration between public media organizations in Oregon and Washington.