A healthy spawning run from one salmon species may play an important role in the health of others, new research from Simon Fraser University suggests.
It’s widely understood when salmon returns are low, dominant fish from other species will push out all smaller competitors to feed on the eggs. But in a study published this week in the journal Ecosphere, researchers from SFU’s Salmon Watershed Lab found when returns are high, the dominant fish will still fill their bellies, but also make room for the younger ones to share in the nutrient-rich feast.
“What we found really interesting is that the competition broke down,” Colin Bailey, lead researcher and PhD candidate said. “Typically when you read about competition with stream fish, the larger fish hold their territory — the larger or more dominate species out-compete the smaller fish. In this case, where we placed a high but realistic number of eggs, the competition dissolved. Small fish gained access to a really really high-quality food source.”
For the study, Abundance of salmon key to feeding ‘underdog’ stream fishes, Bailey and biological sciences professor Jonathan Moore added between six and 3,575 pink salmon eggs in different locations of the Keogh River on Vancouver Island.
Fish were captured and lightly anesthetized to have their stomachs flushed and examined. (The fish recovered in an in-stream container before their release back into the river.)
The team found young coho salmon, small steelhead trout and bottom-dwelling sculpins were able to access large deposits of pink salmon eggs despite other dominant fishes.
The results suggest one species’ spawning numbers impacts food resources for entire fish communities.
Bailey is planning future research on the subject, including this study’s possible connection to his previous research looking at the impacts of pink salmon runs on juvenile steelhead. In that study he found higher runs of pink salmon in the fall coincided with an earlier out-migration of steelhead in the spring. He said it’s commonly accepted in the scientific field that younger fish have less chance of survival during out migration, but there may be more to it.
“If you go to sea smaller you may not have a good chance of surviving, but maybe all that energy you acquire from pink salmon eggs the previous fall compensates for that,” Bailey said.
If the results follow his reasoning, it could potentially influence fisheries management policy in such ways as limiting harvests of large salmon runs where steelhead are struggling.