News from the River: Salmon on the Rebound

Fall-run Chinook salmon migrate from the ocean and begin arriving in the Mokelumne River in late-summer and early fall to spawn. Many salmon enter the Mokelumne River Fish Hatchery at the base of EBMUD's Camanche Dam where eggs are collected and incubated. Other salmon may choose to spawn in gravel beds throughout a 10-mile section of the river just downstream of the dam. The first six months of a juvenile salmon's life begins with a long journey out to sea during which survival is influenced by both anthropogenic impacts and environmental processes. Natural-origin salmon spawned in the Mokelumne River must negotiate a maze of natural and man-made tributaries, sloughs, and river channels as they migrate through the interior Delta to reach the Pacific Ocean. It has been shown that juvenile salmon that migrate through the interior Delta consistently experience reduced survival compared to the Sacramento River. Two to three years later, they return to the river to complete their life cycle. In the fall, fish counts tell us how well these fish have done.

Why so many fish?

Salmon returns are typically cyclical and depend on many factors. They often decline in dry years with warmer ocean temperatures and increase in wet years with cool ocean temperatures. When this year's returning salmon were first on their way to the ocean as young smolts, they were fortunate to find great ocean conditions. When these fish began their return trip to the Mokelumne River, river management changes allowed the returning adults to better able find their way back to the Mokelumne, with less fish straying to the American River.

EBMUD and its partners (California Department of Fish and Game, the U.S. Fish and Wildlife Service, and the National Marine Fisheries Service) use many strategies to protect the fishery, including:

• Minimizing predators. EBMUD, with assistance from the Department of Fish and Game and Woodbridge Irrigation District, removed non-native predator fish below Woodbridge Dam to improve the survival rate of young salmon as they migrate out through the lower Mokelumne River and out to the Pacific Ocean.
• Hatchery release location. EBMUD and the Department of Fish and Game have collaborated to pinpoint release locations that increase survival and reduce straying rates. Release locations, utilized in 2009 and 2010, have proven to be beneficial.
• Attracting the fish. The Delta is a complex system of waterways. It's easy for salmon to lose their way and end up in a different waterway than their natal stream. In some years, about half of Mokelumne salmon have strayed to the American River. In the past two years, experimental pulse flows on the Mokelumne have been used to mimic storm flows and attract fish upstream, past the areas where they may stray to the American River. Also, the closure of the Delta Cross Channel for a few days when salmon migrate in the fall helped more Mokelumne origin salmon find their way back to the Mokelumne River. With the channel closed, fish couldn't be tempted to swim to the Sacramento River through the Delta Cross Channel.
• Improving habitat. EBMUD and its partners add gravel to the river to increase the amount and quality of the natural spawning habitat. EBMUD also works with staff and volunteers to clean up the river.

In the long term, EBMUD and its partner agencies believe that by improving habitat, modifying hatchery practices, better coordinating Delta operations and continuing the robust scientific study program on the river, the Mokelumne salmon return will continue to increase and be a model for recovery on other Central Valley river systems.