Earth.com: Steelhead follow their instincts

Earth.com highlighted work by University of Cincinnati biologist Michael Booth to unlock the migration secrets of an endangered California fish.

Booth, a UC visiting assistant professor of biology, spent years studying southern California's steelhead in the Santa Clara River outside Los Angeles. This subpopulation of rainbow trout migrates to the Pacific Ocean, where the growing fish hunt and feed until they return to their natal freshwater streams to spawn.

While working at the United Water Conservation District, Booth used 19 years of records from a designated fish trap on southern California’s Santa Clara River to identify potential environmental drivers that spur some fish to make the arduous trip to the Pacific Ocean

 He found that steelhead migration was triggered by the lengthening daylight of spring rather than factors like recent rains, which had little correlation to migration.

The study was published in the North American Journal of Fisheries Management.

Since the river in most years is only navigable after storms get water flowing again, Booth hypothesized that heavy rains triggered the steelhead’s movement to the ocean.

“We thought the fish would migrate when the river was flowing and wouldn’t migrate in years without storm events,” Booth said. “It turned out that wasn’t the case. They migrated regardless of whether the river was flowing to the ocean.”

Booth's research is significant because it could help wildlife managers and government regulators make more informed decisions about water use. The Santa Clara River is a major source of water for agriculture and people who live in the watershed. Knowing what months are crucial for steelhead migration could help wildlife managers avoid conflicts.

“It’s really hard for a water manager to decide this is when we can and can’t divert water if you have no data on when the fish are migrating,” Booth said.

Read more about Booth's research.

Featured image at top: Steelhead. Photo/NOAA