Chinook Salmon returns on Mokelumne River continue record streak

EBMUD partnership pays off with successful fishery efforts.

CLEMENTS, CA – East Bay Municipal Utility District (EBMUD)’s Mokelumne River partnership with state and federal natural resources agencies is paying off. With one month left in the fall-run season, over 14,000 Chinook salmon have migrated to the Mokelumne River, continuing a record streak of returns dating back to 2011. For the second consecutive year, the Mokelumne River Fish Hatchery has record numbers of steelhead entering the ladder. Together, the high returns for these species indicate the health of the Mokelumne River, which also supplies water to 1.4 million East Bay customers.

The Mokelumne River is prospering thanks to a collaborative partnership between the East Bay Municipal Utility District (EBMUD), United States Fish and Wildlife Service (USFWS) and the California Department of Fish and Wildlife (CDFW). These agencies have spent nearly two decades developing and implementing a plan to improve spawning and rearing habitat in the river below Camanche Dam.

“As a water agency that is a vital partner on the Mokelumne River, we’re thrilled to see continuously strong returns,” said EBMUD Manager of Fishery and Wildlife Jose Setka. “For EBMUD, the health of natural ecosystems is critical to our watersheds and a vital part of our mission. This river partnership has enabled management decisions that have improved the survival of salmon and steelhead. By improving habitat, updating hatchery practices, better coordinating Delta operations and continuing scientific studies, the Mokelumne River fish population will be model for recovery.”

The impressive fall returns are a result of combined efforts that have focused on water operations, including managing cold water in Camanche and Pardee reservoirs to attract salmon, releasing pulse flows, Delta Cross Channel gate closures, and using tagging data to evaluate hatchery release strategies. Additional innovative measures include transporting juvenile salmon by barge and feeding a specialized diet to assist the freshwater-to-seawater transfer.

The standout season has welcomed over 14,000 adult salmon, compared to 4,129 at this point last year —and is on track to break the 2011 historic record return of 18,000. The number of steelhead has more than tripled with more than 350 steelhead returning this season, compared to historical returns averaging about 100 steelhead per year. This follows last year’s record return of about 600 steelhead.

“This is a wonderful partnership that's making a difference in Mokelumne River salmon and steelhead returns,” said Jay Rowan, senior environmental scientist, supervisor for CDFW's northern and central region hatcheries. “There's been a lot of cooperation and innovation taking place at the Mokelumne River Fish Hatchery in recent years and the fish are benefitting as a result.”

The collaboration between USFWS, CDFW and EBMUD is part of a 1998 agreement between the East Bay utility and federal and state agencies to promote healthier conditions and water flows in the Mokelumne River. The Mokelumne River Fish Hatchery is one component helping sustain the long-term viability of salmon and steelhead fisheries in the river.
The strategies for improved returns included:

  • Stronger Pulses - Pulse flows reached higher magnitudes compared to recent years thanks to flood control waters released from Camanche Reservoir. These pulses provide cues for salmon to move up into the river. Additional pulses provided by reoperating Woodbridge Irrigation District Dam extended the period of pulses into November.
  • Gate Closures – To prevent straying of Sacramento and Mokelumne River salmon, CDFW coordinated closures of the Delta Cross Channel Gates on weekdays and reopened for weekend recreation beginning in September.
  • Tagging Data – Using Coded Wire Tag data from returning fish, the agencies measured the effectiveness of releasing fish on outgoing tides and limiting releases to no more than two consecutive days from the same location to increase juvenile salmon survival.
  • Barging - The agencies have transported juvenile salmon from the Mokelumne River by barge and released them in the San Francisco Bay. Barging improves fish survival through the Delta and may also help with imprinting for juvenile salmon to re-trace their way to natal waters.
  • Transfer Diet – Juvenile salmon undergo an incredible physiological change when moving from freshwater to saltwater. To ease the initial stress, a specialized feed containing higher salt levels is fed to the juveniles in the weeks before the release.
  • Habitat Improvement – working with our partners, EBMUD has restored spawning beds within the river and surrounding riparian habitat. Efforts have included working with local landowners to help identify win - win restoration projects that they could implement on their land.

EBMUD and its partners continue to look for ways to maximize salmon and steelhead survival and protect the health of California’s fish and the Mokelumne River.

EBMUD has a proud history of providing high-quality drinking water for 1.4 million customers in Alameda and Contra Costa counties. The District’s wastewater treatment serves 685,000 customers and protects the San Francisco Bay.