DNA analysis reveals pink salmon swim home with incredible accuracy

Sampling_Paddy_Creek_w_ 3 bears_MartaRee

Above: Researchers Julia McMahon, left, and Pete Rand measure and take tissue samples from pink salmon carcasses in Paddy Creek where it flows into Prince William Sound, Alaska, as black bears hunt in the background. (Photo by Marta Ulaski)

By Jeff Richardson

Analysis of a massive database of pink salmon DNA has revealed unexpected details about the abundant salmon species, including its ability to return to spawn at nearly the same spot within streams as their parents.

Samuel May, a postdoctoral fellow at the University of Alaska Fairbanks College of Fisheries and Ocean Sciences, led a project that reviewed genetic data from over 30,000 pink salmon.

The effort taps into an ongoing study in Prince William Sound in Alaska that has collected DNA samples from pink salmon carcasses since 2011.

The Alaska Hatchery Research Program samples pink salmon in 30 streams, including five where they attempt to collect samples from every salmon returning to spawn.

The AHRP is a collaboration between the Alaska Department of Fish and Game, nonprofit hatcheries, the fishing industry and academia, including UAF.

It is largely focused on the impact of hatchery fish on wild salmon populations. Beyond that topic, the database provides a trove of information for researchers exploring other questions.

“We can connect the parents and offspring from multiple populations, along with body size, when they were sampled and where they were sampled,” May said. “There’s all this fine-scale diversity that we didn’t really appreciate before.”

One of the most striking findings was the salmon’s ability to detect the specific location where it hatched.

Pinks don’t just return to a home stream or tideland: After traveling thousands of kilometers, they generally spawn within 100 meters of the point where their parents spawned.

Genetic analysis also highlighted distinctions between areas within the streams where pinks spawn.

About 75% of the salmon spawn in intertidal areas, a zone affected by regular saltwater intrusion and apparently preferred by wild pinks.

Hatchery-origin pink salmon tend to travel into freshwater areas of those streams to reproduce.

There they may be more likely to mate with other fish that also were stocked by hatcheries in those locations.

Their origins are also associated with a variety of biological differences, including body size and reproductive success.

Pink salmon haven’t received the same attention from researchers as other salmon species because they’re often viewed as homogenous — spawning pinks are all 2 years old and roughly the same size.

Through DNA analysis, researchers are revealing a more diverse species, which should help its ability to adapt as the climate changes, May said.

“All this variation impacts the ability of this species to persist in the face of change,” he said.

Such findings are just the beginning, said CFOS associate professor Peter Westley, who contributed to the study and is a member of the AHRP’s Science Panel.

Within a few years, there will be more than 200,000 pinks in the AHRP genetic database.

That expanding catalog will give researchers the ability to discern offspring success at various locations, determine how often spawning pinks stray from their hatch sites, and explore the broader effects that the fish are having on the ecosystem.

“We’re leaning on a dataset that’s had a ton of work put into it,” Westley said. “This is just the tip of the iceberg.”

Below: Pink salmon spawn in Gilmour Creek near where it enters Prince William Sound, Alaska, as a field technician works to collect carcasses of dead fish. (Photo by Kate Ruck)