The finding, by UC Davis graduate student Tasha Thompson and colleagues, helps distinguish between spring- and fall-run fish—and could help save spring-run salmon from human-hastened extinction. Fall-run populations enter rivers in autumn and spawn immediately. By contrast, spring-run fish return during peak snowmelt, linger in tributaries through summer, and spawn around the same time as their fall-run brethren. “Spring-run fish are special for a lot of reasons,” Thompson says. Spring-run salmon historically spawned in the upper portion of watersheds, nourishing ecosystems with marine nutrients when they died. Today, these habitat preferences have left spring-run Chinook vulnerable thanks to dams, logging, climate change, and other human-caused alterations to their habitat. “People once thought spring-runs would easily evolve from fall because they’re so closely related within the same river,” Thompson says. But her research finds that less than 0.5 percent of the fish in the Shasta and Scott rivers, which lost their spring runs decades ago, still possess the spring-run variant. “That’s a level that can’t be considered sustainable for maintaining the spring-run gene,” she says. Yet all is not necessarily lost for these fish. Dam removals on the Klamath will reopen hundreds of miles of upper watershed spawning habitat by 2021. And the new genetic test should improve management of spring-run fishes, enabling scientists to survey populations and guide conservation efforts.
Photo: Jan Jaap Dekker
Pearls in the ocean of information that our reporters didn’t want you to miss
2012 Salmon River Spring Chinook Salmon Survey Dive
 

A gene tells Chinook salmon whether to return to their native streams to spawn in spring, fall, or sometime in-between, according to new research.

The finding, by UC Davis graduate student Tasha Thompson and colleagues, helps distinguish between spring- and fall-run fish—and could help save spring-run salmon from human-hastened extinction. Fall-run populations enter rivers in autumn and spawn immediately. By contrast, spring-run fish return during peak snowmelt, linger in tributaries through summer, and spawn around the same time as their fall-run brethren. “Spring-run fish are special for a lot of reasons,” Thompson says. Spring-run salmon historically spawned in the upper portion of watersheds, nourishing ecosystems with marine nutrients when they died. Today, these habitat preferences have left spring-run Chinook vulnerable thanks to dams, logging, climate change, and other human-caused alterations to their habitat. “People once thought spring-runs would easily evolve from fall because they’re so closely related within the same river,” Thompson says. But her research finds that less than 0.5 percent of the fish in the Shasta and Scott rivers, which lost their spring runs decades ago, still possess the spring-run variant. “That’s a level that can’t be considered sustainable for maintaining the spring-run gene,” she says. Yet all is not necessarily lost for these fish. Dam removals on the Klamath will reopen hundreds of miles of upper watershed spawning habitat by 2021. And the new genetic test should improve management of spring-run fishes, enabling scientists to survey populations and guide conservation efforts.
Photo: Jan Jaap Dekker

About the author

Bay Area native Kathleen M. Wong is a science writer specializing in the natural history and environment of California and the West. With Ariel Rubissow Okamoto, she coauthored Natural History of San Francisco Bay (UC Press, 2011), for which she shared the 2013 Harold Gilliam Award for Excellence in Environmental Reporting. She reports on native species, climate change, and environmental conditions for Estuary, and is the science writer of the University of California Natural Reserve System.