Klamath River steelhead: a diverse portfolio

By Brian Hodge

Just as investors diversify their portfolio of assets to minimize financial loss, fisheries managers may diversify their portfolio of conservation strategies to minimize species loss (TU’s Science Team has published some great literature on the subject).

Another fishy analog for the “portfolio effect” comes from the steelhead—it reduces risk of extinction by displaying a diverse array of life histories, or pathways from hatch to spawn.

My colleagues and I found that wild Klamath River steelhead, for example, display at least 38 different life histories¹. They spend from 1 to 3 years in freshwater before heading out to sea, and from 2 months to 4 years at sea before returning to freshwater to spawn. Some fish (“half-pounders”) return from the ocean for reasons other than spawning, whereas others (rainbow trout) spawn without ever leaving freshwater. Fish of both sea-run and freshwater forms are capable of spawning repeatedly (up to four times) in a life span. Further complicating matters, steelhead mothers can give rise to rainbow trout, and rainbow trout mothers can give rise to steelhead.

The benefit of all this diversity is dispersal of risk—in simple terms, Klamath River steelhead put their eggs into a relatively large number of baskets, and in doing so, stabilize the population over the long term.

Our Klamath River steelhead study follows upon recent news that parties of the Klamath Hydropower Settlement Agreement took a critical step forward with an Agreement-in-Principle. Implementation of the Hydropower Agreement would remove four major dams from the main stem Klamath River and restore access to approximately 400 miles of historical steelhead and salmon habitat. 

Dr. Walt Duffy, a co-author of the steelhead study and emeritus faculty member at Humboldt State University (Department of Fisheries Biology), noted that "it will be interesting to see how the life history of Klamath steelhead changes with access to more than 400 miles of additional habitat." Some predict that dam removal will lead to even more life history diversity among Klamath River salmonids.

When we look at the steelhead, we can see why part of managing for an effective conservation portfolio is managing for a diverse life history portfolio.

Brian Hodge is a fisheries biologist and project coordinator for Trout Unlimited in Colorado.

¹Hodge, B. W., M. A. Wilzbach, W. G. Duffy, R. M. Quiñones, and J. A. Hobbs.  2016.  Life history diversity in Klamath River steelhead.  Transactions of the American Fisheries Society 145:227-238.

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