Chinook salmon benefit from social interactions when navigating fish ladders

Chinook salmon spawning in a Pacific Northwest river. iStock

Throughout the animal kingdom there are many advantages to migrating in large numbers. One such benefit is “collective navigation,” where the social interactions among animals improve the group’s ability to find its way.

A new University of Washington study has found that Chinook salmon seem to use collective navigation and interact socially to help each other find fish ladders at dams. The findings were published on Oct. 21st in the Proceedings of the Royal Society B.

A fish ladder along dam, Oregon. iStock

Salmon migrating upriver often encounter blockages and obstructions they need to circumvent. The implementation of fish ladders alongside large dams have provided salmon with a way to forge ahead, though they still face the challenge of locating, entering, and traversing these fishways.

Researchers analyzed the spawning migrations of adult Chinook and sockeye salmon in the Columbia River Basin from 2013–2014. They found that Chinook salmon were able to navigate fish ladders more quickly on days when there were more Chinook present.

“Large groups of fish appear to have an easier time finding the entrances to fish ladders and passing through them,” said Connie Okasaki, a doctoral student in Quantitative Ecology and Resource Management. “We take that to mean some sort of collective behaviors are at play.”

Sockeye salmon swimming upstream. iStock

While larger groups of Chinook may have a navigational advantage, by contrast, sockeye salmon seem to neither help nor hurt each other during migrations. Ironically, this may be because sockeye tend to be more social and form very tight knit schools.

“It appears that sockeye are almost too social; they’re acting as a unit, as if the group were a single individual acting alone,” says Okasaki. “Whereas Chinook form much looser aggregations in which the whole community present at the dam is trying to navigate and help each other.”

The study suggests that changes in population could be magnified in Chinook salmon due to this behavior: large, healthy populations of salmon should have an easier time staying healthy, while small struggling populations will have a harder time maintaining their numbers. The migration gets more difficult when there is a smaller “team” to help out.

A swimming salmon in Bradford Island Fishway at the Bonneville Dam in Oregon. iStock

Salmon runs, particularly those in the Columbia River, face many challenges. These new insights into how salmon migrate using collective navigation have the potential to become key components in management decisions.

“Salmon are a stunning example of perseverance as they make the difficult journey upstream. The idea that that journey may also involve teamwork, humanizes these fascinating creatures further and only adds to their charismatic appeal,” said Okasaki.

Other co-authors are Matthew Keefer of the University of Idaho; Peter Westley of the University of Alaska Fairbanks; and Andrew Berdahl, UW professor of aquatic and fishery sciences. This research is based upon work supported by the NSF-GRFP under Grant No. DGE-1762114.

For more information, contact Okasaki at cokasaki@uw.edu.

Related story: Early-arriving endangered Chinook salmon take the brunt of sea lion predation on the Columbia

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