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Freshwater life-histories of Steelhead Trout controlled by environment and co-occurring pink salmon

A new study from the Salmon Watersheds Lab, led by PhD student Colin Bailey, discovered that juvenile steelhead life-histories seem to respond to multiple factors in the freshwater environment. This study examined 40 years of data on age, size, and abundance of juvenile steelhead trout migrating to sea in a well-studied population in northern Vancouver Island.

Juvenile steelhead may migrate to sea after spending between 1 – 5 years in their natal stream. However, following large runs of pink salmon or artificial nutrient addition, juvenile steelhead often migrated to sea at younger ages. Pink salmon eggs released during spawning are likely an important food source for young steelhead. Smolts also tended to be larger for their age following artificial nutrient addition and/or years when it was warmer. 

The number of smolts produced was also associated with multiple factors. First, there was strong evidence for population regulation; the number of smolts per spawner was lower when there were more spawners. Both nutrient addition and lower air temperatures were associated with greater juvenile steelhead production prior to 1991, while greater pink salmon abundance was associated with greater juvenile steelhead production after 1990.

A 4-decade time-series of data collected at the Keogh River, Port Hardy, BC was used to characterize links between the steelhead life cycle and environmental factors. Since the early 1970s, information has been collected from the Keogh River using fish fences, angling, and a resistivity counter (a way of counting fish by detecting the drop in electrical resistance as fish pass over low energy electrical current). These data would not exist without the on-going collaboration between the Department of Fisheries and Oceans Canada, British Columbia Ministry of the Forests, Lands, Natural Resource Operations and Rural Development, and Instream Fisheries Research to monitor Keogh River salmonids.

Although these results come from a single stream, they suggest that steelhead life-histories are quite responsive to their environment. For instance, it is possible that larger returns of co-occurring pink salmon might slightly increase the production of juvenile steelhead.

Bailey, C. J., D. C. Braun, D. McCubbing, J. D. Reynolds, B. Ward, T. D. Davies, and J. W. Moore. 2018. The roles of extrinsic and intrinsic factors in the freshwater life-history dynamics of a migratory salmonid. Ecosphere 9(9): e02397. 10.1002/ecs2.2397 (link)

Media: SFU News

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