Scientists investigate social patterns of salmon

Each summer, millions of fish return to Bristol Bay, and then swim on to the stream where they were born to spawn, and die. Exactly what compels them to return to the right spot is unknown. But scientists think that some hatchery-raised steelhead in Oregon might hold a clue.

“Chinook salmon, Yukon Delta NWR.” Photo: Craig Springer, U.S. Fish & Wildlife Service. Via Flickr Creative Commons.
“Chinook salmon, Yukon Delta NWR.” Photo: Craig Springer, U.S. Fish & Wildlife Service. Via Flickr Creative Commons.

Are salmon social creatures? That’s the question a pair of researchers are trying to figure out.

“50 some million fish last season migrated into Bristol Bay in the course of just a couple of weeks, and that’s a classic thing is that the fish all come at the same time, and it’s kind of curious to think, is there a potential social role in that?” said UAF Fisheries Professor Peter Westley. “They all come as a major wave, and is it because they are in these groups and they are sort of following the leader and using social dynamics to aid their migrations.”

By digging fake streams at an Oregon lab, Westley and colleague Andrew Berdahl are trying to figure why salmon choose the streams they do.

“So we actually tested this idea by giving steelhead that had migrated home to a hatchery, we brought them to the Oregon Hatchery Research Center and gave them a choice between water that smelled more like home, or all of the foreign water that came from the stream where the hatchery research center was based,” Westley said. “One of the things we showed with this steelhead system that indeed, fish that are moving upstream and are moving around ARE very social. They don’t move independently. They’re in groups moving around.”

Westley said there are plenty of details still to work out, and so far, they just have a tantalizing teaser of some possible results. But it’s a little step closer to figuring out what compels salmon to come home each year.

Westley and Berdahl have been interested in this social side of fish behavior for some time, and their collaboration started with a paper that just looked at existing literature and data.

“It poses this idea of a collective social role of salmon as they are migrating home, such that salmon or other migratory fish can school together,” said Westley. “And by being in groups, they can share information and pool their abilities to navigate and orient and by doing so the group is much more likely to get home than if the group was smaller or the individual is traveling by itself and the onus of getting to the right spot would all be on the individual.”

Westley said smell, or pheromones, play a role in salmon communication. But that’s part of what he’d like to test. Westley said steelhead are a good proxy for salmon because they’re pretty similar fish in terms of life history and a predictable return to their birthplace.

“They are a good model for these migratory sea-going fish that come back home,” Westley said. “They have subtle differences in life history but in terms of the social aspects and the migration and the orientation, I think they are a good model.”

Not everything about the study is a direct translation to the natural world, and there are plenty of changes and questions to address in the future. Westley said they hope to do the experiment again, with a stronger scent of home-streams. And they might change the timing of the study, to tie in more closely to when salmon are actually on the move. Somewhere on the list, he said, he’d also like to look at how wild fish fare, rather than just using hatchery steelhead – a choice made, so far, to keep things simple.

“The challenge is always trying to scale from what you’re doing at sort of an experimental level up into the complexity of nature, and trying to assess what you’ve done at this small controlled scale, does it relate to nature as a whole,” said Westley. “It’s always a challenge.”

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