Walking along a stretch of the Mokelumne River at the Mokelumne River Hatchery in Clements on Thursday morning, EBMUD’s manager of fisheries and wildlife pointed to salmon spawning near the riverbank.“An average adult salmon has about 5,000 eggs in them, and about 4,000 make it to the nest,” Jose Setka said. “In the hatchery, of course, they take all of the eggs.”
Run by EBMUD and the California Department of Fish and Wildlife, the hatchery has seen approximately 14,800 salmon return as of Wednesday, slightly less than the 16,500 salmon at this time last year.
Despite being one of the smallest rivers in the Sacramento-San Joaquin River Delta, the Mokelumne’s salmon population made up approximately 20 percent of the commercial catch and approximately 30 percent of the recreation catch for California’s coast last year.
The spawning season usually lasts from October through December, Setka said, and the juvenile salmon are released in late April through May of the following year.
While some salmon spawn in shallow portions of the river, others swim toward a fence that steers the fish toward a gate which controls how many are let into the “ladder,” a narrow man-made stream that leads the fish toward the hatchery.
The salmon then make their way to a conveyor belt inside the hatchery building where employees separate the males and females before fertilizing the eggs and collecting them in large plastic tubs to incubate.
Before releasing the young salmon from the fresh waters of the Mokelumne River to the salt waters of the Pacific Ocean, however, Setka said hatchery employees feed the fish a diet with more salt than they would normally eat.
“That will start to trigger that transformation and make the transition easier,” Setka said.
Although he does not expect this year’s salmon run to meet or exceed last year’s record-breaking run of 19,954 salmon, Setka was optimistic that the hatchery will continue its fruitful spawning season in the coming weeks.
“Since the new flow regime in the mid-1990s, our average has been about 9,000 fish per year,” Setka said. “No matter how you slice it, it’s been another successful year.”
CDFW supervisor Jay Rowan also felt that this year’s spawning season has been successful so far, he said, citing the partnership between CDFW and EBMUD as one of the primary reasons.
“They take the salmon run seriously, and make it a priority to have a good hatchery,” Rowan said of EBMUD. “CDFW and EBMUD have a really good partnership and this shows what we can do when we work together.”
John McManus, president of the Golden Gate Salmon Association — which represents both sport and commercial salmon fisherman in California — praised the hatchery for the amount of salmon they release each year as he watched the employees process the fish.
“EBMUD encourages innovation with their hatchery practices,” McManus said. “Salmon fishermen see what’s going on, and we greatly appreciate this operation.”