Coho eating sockeye egg, credit: Jonny Armstrong

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Abundance of salmon key to feeding 'underdog' stream fishes: SFU research

September 23, 2020
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By Melissa Shaw

Researchers from Simon Fraser University’s Salmon Watershed Lab have found when salmon returns are high, smaller and less dominant fishes get a chance to feast on their eggs.

For their study, published in the journal Ecosphere, SFU PhD candidate Colin Bailey and biological sciences professor Jonathan Moore experimented with adding between six and 3,575 pink salmon eggs to different stretches of the Keogh River on Vancouver Island.

To determine which species and what sizes of fish were eating the salmon eggs, fish were captured, lightly anesthetized and their stomachs flushed. They were placed in a recovery container in the stream before being released back into the river. This also helped the researchers to see how the sudden abundance of food was disrupting the normal dominance hierarchy among stream fishes.

The researchers found that less dominant fish, such as young Coho salmon and small steelhead trout, and bottom-dwelling sculpins benefited from large quantities of salmon eggs in these experiments.

“When food is regular and sparse, the largest fish in a stream will generally dominate and eat the food,” says Bailey, the study’s lead researcher. “But when salmon eggs are abundant during years of high salmon returns, these larger bullies get full and the rest of the fish in the food web can feast.”

He says the current study suggests that declines in the number of spawning salmon could negatively impact food resources for the entire fish communities more than previously realized. In the Keogh River, pink salmon runs typically produce abundant drifting salmon eggs in years of high salmon returns. In other rivers in British Columbia, large pink, chum or sockeye salmon runs have the potential to generate similar feeding opportunities for ‘underdog’ fishes.

Coho feeding, credit: Jonny Armstrong

Future research will examine whether this boost of energy and nutrient rich food increases survival of these young fish as they get older. If so, then more pink salmon may help translate into more steelhead or coho and the fisheries they support.

The study points to the importance of sustainably managed salmon fisheries as crucial to ensuring a healthy freshwater ecosystem and consistent fishing opportunities for years to come.