Resource pulses level the playing field and benefit ‘underdog’ stream fishes
Researchers from the 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, recently published in Ecosphere, PhD candidate Colin Bailey and 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 caught, lightly anesthetized and their stomachs flushed before a recovery and release back into the stream. This helped the researchers to see how the sudden abundance of food was disrupting the normal dominance hierarchy among stream fishes.
They 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 but when salmon eggs are abundant during years of high salmon returns, these larger fish get full and the rest of the fish in the food web can feast.
The current study suggests that declines in the number of spawning salmon could impact food resources for the entire fish communities. In the Keogh River, pink salmon runs typically produce abundant drifting salmon eggs in years of high 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.
Bailey, C.J., and J.W. Moore. 2020. Resource pulses increase the diversity of successful competitors in a multi-species stream fish assemblage. Ecosphere. 11(9): e03211. doi: 10.1002/ecs2.3211. (PDF).