Some species, like salmon, spend most of their lives in the ocean and return to their birthplace to spawn.
“A salmon will go out of its stream and then it’ll go in the middle and mix with a bunch of different populations,” said Wes Larson, the genetics program manager at the NOAA Alaska Fisheries Science Center and co-author of a paper published last month on sablefish genetics. “So it would be like the one that would go to New York for college and then come back home.”
Larson said that sablefish, or black cod, don’t return home to spawn. In this analogy, if salmon move back home to settle down, black cod tend to meet someone abroad and start a family.
“The sablefish, it’s doing its thing, it’s eating, it’s swimming around finding food, and then we think basically, it just sort of spawns close-ish to where it’s at,” Larson said.
That tendency to mate randomly is called panmixia, and it means that Alaska doesn’t have genetically distinct populations of sablefish. A sablefish born in the Bering Sea could mate with a Southeast sablefish — or with a fish from up north.
Larson said there are limits on that mixing.
“It’s not equally probable that a fish from Mexico will come up to Alaska compared to, like, a fish from northern B.C., but the panmixia means that there’s enough exchange across the whole range,” he said.
Larson said that understanding that kind of genetic variation is important in fisheries management.
“When you’re setting quotas and things like that, it’s important to know whether you’re fishing on a stock that exchanges with other stocks or a stock that doesn’t, because if you don’t know that information, and let’s say it’s structured, you can really fish down a certain area,” he said. “If they don’t exchange with other areas, then you can basically fish that out, essentially.”
Larson and other researchers did a deep dive into Alaska’s sablefish populations, using advanced techniques to map and compare the entire genetic footprints of juvenile and adult sablefish across Alaska and Washington.
Although previous studies have shown evidence of panmixia, a 2023 study by Mexican researchers suggested that Alaska sablefish might actually have distinct populations. Larson said that’s part of the reason that he and other researchers wanted to publish new data.
“If management took that microsatellite paper, that would sort of change the management paradigm,” Larson said. “Which, if it’s real, is important, but we didn’t think it was real.”
Larson said the new data, which used millions of genetic markers, provides a much higher-resolution picture of the population – and confirms that fisheries managers are using an appropriate framework to manage Alaska sablefish.