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Hidden biodiversity maintains resilience of steelhead populations


A recent study on steelhead from the Skeena and Nass rivers uncovered remarkable hidden diversity in steelhead life cycles and discovered that this biodiversity stabilizes these populations. The remarkable hidden biodiversity of steelhead in the Skeena and Nass watersheds is likely the result of relatively pristine habitats and centuries of local adaptation, unpolluted by hatchery influence. Other watersheds have likely lost diversity due to hatchery propagation and habitat degradation.These historic losses make the remarkable biodiversity and its buffering capacity of Skeena and Nass steelhead particularly notable.

Read the paper.


Key findings of our study:

  • Steelhead completed their life cycle in 36 different ways, the most ever documented for steelhead populations. They spent two to six years in freshwater and one to four years in the ocean. Some individuals spawn once, while others made up to four spawning migrations. These different life cycles represent an important form of biodiversity that is often overlooked or hidden.

  • Just like investment managers can minimize their financial risk by diversification of their stock portfolios, the diversity of steelhead life-cycles also buffers risk to the population. For example, if there is a bad year in early-marine survival, cohorts with different ocean-entry year will smooth over the effect of this environmental variability and enable more stable adult steelhead returns. This study estimated that this “portfolio effect” made steelhead abundances at least 20% more stable.

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