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Tracking Study Seeks Secrets of Some of the Sacramento’s Most Successful Salmon

May 21, 2024

Spring-run Chinook salmon from Butte Creek grow faster and survive better.

Juvenile Chinook in a scale, weighing 19.6 grams Biologists measure and weigh a juvenile spring-Chinook salmon from Butte Creek. Photo: Jeremy Notch/SWFSC

Researchers are tracking one of the most successful populations of young Chinook salmon on the Sacramento River downstream to the ocean—and you can, too.

The researchers want to unravel the details behind the relative success of spring-run Chinook salmon from Butte Creek. Even as the species struggles, the fish from Butte Creek are growing faster and surviving at higher rates. They’re also returning in greater numbers than other spring-run populations in California’s Central Valley. Biologists hope the secrets of their success might help slow and perhaps reverse the decline of the threatened species. These declines have recently led to urgent measures by state and federal officials.

In April, biologists from NOAA Fisheries and UC Santa Cruz fitted more than 200 of the Butte Creek fish with tracking tags. You can track that display their migration through the treacherous Sacramento-San Joaquin Delta to the ocean. The website also includes other tracking studies. Their journey through the maze-like Delta is fraught with invasive predators, giant pumps so powerful they alter currents, and dead-end canals where they can perish.

“We want to understand how these fish navigate their downstream migration,” said Jeremy Notch, a research fisheries biologist based at UC Santa Cruz and affiliated with NOAA Fisheries’ Southwest Fisheries Science Center. “Are they doing anything different than other fish, and are more of them making it out to the ocean in good shape?”

Biologists holding a seine net in the water
Biologists use a seine net to collect juvenile spring-run Chinook salmon for tagging. Photo: Jeremy Notch/SWFSC

Follow fishes progress

You can see their progress from Butte Creek, down the Sacramento River, and through the Delta as receivers along the way detect signals from their tags. The tagged fish were released about a month ago. So far, fewer than 10 percent have made it all the way past the final receiver at the entrance to San Francisco Bay.

While the survival rate is low, it is higher than many other Chinook salmon runs. One key to success for the Butte Creek Chinook is their access to productive floodplain habitat in an area called the Butte Sink. They can access the area through the winter and early spring, when managers divert much of Butte Creek into the floodplain to attract waterfowl for hunting. Recent studies have found that salmon grow quickly in the rich wetlands of the sprawling floodplain. They begin their downstream migration before most other runs, benefiting from higher flows that help them travel faster.

“The life history of these fish give them several advantages that combine to improve their overall odds of finally returning as an adult to spawn,” Notch said.

Sacramento River spring-run Chinook are a threatened species. Despite the relative success of Butte Creek salmon, the species overall has declined to alarming lows during the last decade of frequent and extreme drought. Few adult fish returned to the streams that still support them last year. Federal and state biologists are collecting juvenile fish to create a captive breeding program that can safeguard the genetic heritage of the species if they continue to decline in the wild.

Butte Creek fish larger

Limited numbers of adult spring-run Chinook salmon spawned in Butte Creek last fall. However, biologists netted many juvenile fish in Butte Sink pools within the Wild Goose Duck Club. They first tagged 150 fish and released them in different parts of the Sink to gauge their survival through three main migration routes. Most of the fish had grown larger, averaging almost 4 inches, than those in other Sacramento River tributaries.

Grant Henley from The California Department of Fish and Wildlife tagged more than 100 additional fish, bringing the total number of tagged fish to 259.

Depending on the conditions, larger fish may have better odds of survival on the way downstream and once they reach the ocean. The receivers also help scientists track the fish through the Sutter Bypass, which gives them access to more floodplain habitat as they move downstream. The tracks of the tagged fish reveal how fast the fish move and whether they take advantage of such promising habitat on the way.

“What can we learn from this fish about what they are doing and why it works?” Notch said. “If something is relevant to other populations, it may help us restore those which are struggling to persist.”