The rivers in California are still running low thanks to three long years of drought. But instead of struggling, the Chinook salmon of the Mokelumne River are returning to their home waters to spawn in record numbers.
Officials from the East Bay Municipal Utility District reported 12,118 salmon returned to the river in the fall of 2014. It’s the fifth-highest run in 74 years, and nearly triple the river’s long-term average. It’s the fourth year in a row that has returned such high numbers.
A quarter of the fish spawned in the river, while the rest were collected at the Mokelumne River Fish Hatchery for egg production.
“These positive results indicate that our efforts are successful and our partnerships are working,” said EBMUD Manager of Fishery and Wildlife Jose D. Setka. “The Delta is already an unwelcoming place for juvenile salmon and the drought makes those conditions worse. Salmon need all the help they can get.”
But what led to those record numbers? EBMUD biologists got creative and worked with the Woodbridge Irrigation District to change their dam operations.
Salmon are driven by instinct. When the cold fall and winter storms begin sending extra water down the river, they know it’s time to come home. During the drought, those storms are not as strong and happen less often. To signal the fish if that happens, water managers along the river save water during the springtime and release pulse flows in the fall to mimic those storms.
To deal with warmer water in the Mokelumne, EBMUD pulled water from the bottom of Pardee Reservoir for some of the pulse flows to lower the overall temperature in the river. When it’s under 60 degrees, the conditions are better for spawning.
Officials use additional techniques to help young salmon survive. That includes transporting the fish to Sherman Island near Antioch to avoid predators and export pumps in the river.
Regional agencies will develop forecasts for 2015 based on this salmon report and an upcoming snow survey. For the next few months, it’s all about making sure this year’s juvenile salmon survive to return to the river in two or three years.