Maya Roe’s writing has appeared in the Pamlico Writers Group Anthology, Coffin Bell Journal, and other smaller publications. She is currently a student at College of the Atlantic where she studies human ecology with a focus on science communication. This piece is part of a collection of articles Maya is writing about salmon conservation for her senior project.
Protecting California’s Athletic Steelhead:
Diverse steelhead migration patterns give conservationists a leg up on climate change
By Maya Roe
Most people in Northern California are at least somewhat familiar with the story of anadromous fish like steelhead and salmon. The young fish of most anadromous species hatch in the upper watershed and travel downstream to the sea as they mature. As adults, they migrate back up rivers, leaping over impossible looking obstacles with the strength they gained while living in the ocean. After laying and fertilizing their eggs in the upper watershed, many species of anadromous fish die, completing their life cycle. A simplified anadromous life cycle may be a useful way for conservationists and the public to understand salmon; however, recent research and observations are demonstrating that in order to conserve an anadromous species well, conservationists need to understand and protect the variations in life histories within a species. Conserving multiple life histories is important because life history diversity makes a species more resilient to drastic environmental changes. Armed with knowledge about steelhead genetics, Friends of the Eel River (FOER) is working to protect Northern California’s summer steelhead population.
Biodiversity protects species, communities, and watersheds from dramatic fluctuations in climate. As climate change becomes more severe, extreme weather events will become more common and diversity will become more important. When conservationists calculate how well an ecosystem will resist the impacts of climate change, they have noticed that maintaining species diversity and life history diversity makes the ecosystem more resilliant. Fortunately, the Eel River has steelhead that demonstrate two different life histories—the adults enter the Eel River either in late spring before summer sets in or in the fall with the first rains. Recent research from Dr. Michael Miller’s laboratory at the University of California, Davis (UC Davis) suggests that there are significant differences between the two life histories of steelhead in the Eel River, a discovery that led Friends of the Eel River to take action to protect summer steelhead.
Steelhead are an anadromous variety of rainbow trout (Oncorhynchus mykiss) that spend part of their lives in the sea and grow much larger than their non-migratory cousins. The majority of Eel River steelhead are classified as “winter steelhead” based on their life history. They enter the river in the fall as sexually mature adults and travel up the river to spawning grounds in the middle of the watershed. In contrast, “summer steelhead” enter the watershed earlier in the season, when they are not sexually mature. They spend their summer in the shelter of cool, deep pools and press further inland when the first rains swell the rivers. Because they are smaller, more athletic, and have more time to travel, summer steelhead spawn higher in the watershed than winter steelhead.
For a long time, researchers could not establish a significant non-behavioral difference between summer and winter steelhead. However, in 2017, researchers from UC Davis discovered that there is a particular allele that is different in summer and winter steelhead populations. This means that based on the life history of the steelhead, it has a different gene in a certain place on its genome. Remarkably, they also determined that there is an allele at the same locus on the Chinook salmon genome that is different for spring and fall migrators. It is not entirely clear what this allele regulates, but some researchers believe it may control fat storage, which would in turn dictate when the steelhead are ready to enter the watershed.
Discovering that there is a genetic difference between these two populations has made conserving them individually much more important. Miller and his team determined, based on patterns of genetic variation, that the life history split likely only occurred once in the history of the species which means that it is unlikely that one life history would arise from the other life history if one is extirpated. Therefore, maintaining both steelhead life histories is very important. Although winter steelhead populations in the Eel River are reasonably stable, summer steelhead are in serious jeopardy because their habitat has been fragmented by dams. Dams like the Potter Valley Project on the Eel River prevent summer steelhead from traveling up to their spawning grounds in the cool water of the upper watershed. There are actually steelhead with the allele for early migration above the dam, which suggests that their ancestors were trapped above the dam when it was constructed a hundred years ago.
In November of 2018, FOER chose to act on Miller’s research by filing a petition to list Northern California’s summer steelhead as an endangered distinct population segment under the Endangered Species Act. On February 5th 2020, the National Marine Fisheries Service announced the results of a status review of summer steelhead, declining FOER’s request to list summer steelhead as a separate species with ‘endangered’ status. Although this decision is disappointing, Scott Greacen, FOER’s conservation director, reminded me that the decision is the one he expected, and FOER has always assumed they’d have to litigate to secure a federal listing for Northern California summer steelhead. Furthermore, legal protection is one of FOER’s many strategies for protecting life history diversity. Plans to remove Scott Dam grow firmer day by day, and the legal fight for summer steelhead listing is far from over. Although summer steelhead are only a tiny component of the Eel watershed, they are an important reminder that there are many complexities of the life cycles of anadromous fish still waiting to be discovered. And if we do not fight to protect the watershed, some of these complexities many disappear without a trace.
Moore, Jonathan W., et al. “Life‐history diversity and its importance to population stability and persistence of a migratory fish: steelhead in two large North American watersheds.” Journal of Animal Ecology 83.5 (2014): 1035-1046.
Prince, Daniel J., et al. “The evolutionary basis of premature migration in Pacific salmon highlights the utility of genomics for informing conservation.” Science advances 3.8 (2017): e1603198.