A dramatic decline in the number of chinook salmon returning to spawn in the Northern San Joaquin Valley, and elsewhere in California, could lead to severe fishing restrictions.
As of Tuesday, only 1,100 chinook, also known as king salmon, had been counted on the Stanislaus, Tuolumne and Merced rivers.
That's about an 80 percent drop from the previous year, when about 5,800 returning salmon were reported in the three rivers.
"These numbers, while still preliminary, are very disappointing. There is nothing in particular that we can point to at this stage to explain it." said Kate Hora, Modesto Irrigation District spokeswoman.
In the Sacramento River basin, the number of returning chinook also has declined precipitously, leading federal fishery regulators to consider imposing stiff restrictions on salmon fishing this year.
Experts say the dwindling chinook population is part of a broader decline in wild salmon runs across the West.
The number of chinook returning to the Sacramento River and its tributaries is down more than 88 percent from the all-time high recorded five years ago, according to an internal memo sent to members of the Pacific Fishery Management Council and obtained Tuesday by The Associated Press.
About 90,000 returning adult salmon were counted in the Central Valley in 2007, the second-lowest number on record, the memo says.
The population was at 277,000 in 2006 and 804,000 five years ago.
In an e-mail to fishery council members, Donald McIsaac, the agency's executive director, said he wanted to give them "an early alert to what at this point appears to be an unprecedented collapse in the abundance of adult California Central Valley ... fall chinook salmon stocks."
"The magnitude of the low abundance," he wrote, "is such that the opening of all marine and freshwater fisheries impacting this important salmon stock will be questioned."
Last fall, Doug Demko of FishBIO, a consulting firm with offices in Oakdale and Chico, told The Bee that salmon numbers were in decline throughout the West.
Why? Demko and other experts believe changing climate conditions, including warmer water temperatures in the northern Pacific Ocean, could be behind the dramatic decline.
Salmon thrive in colder water.
For years, conventional wisdom in the Northern San Joaquin Valley has been that more water flowing through rivers during the spring would lead to larger numbers of salmon returning to spawn in the fall.
MID officials have speculated that a host of problems could be making life difficult for the fish, including predatory striped bass, declining water quality, warmer water temperatures and delta pumping.
It's only the second time in 35 years that the Central Valley has not met the agency's conservation goal of 122,000 to 180,000 returning fish, according to the council, which regulates Pacific Coast fisheries.
More worrisome is that only about 2,000 2-year-old juvenile chinooks -- used to predict returns of adult spawners in the coming season -- returned to the Central Valley last year, by far the lowest number ever counted. On average, about 40,000 juveniles, or "jacks," return each year.
The Associated Press contributed to this report.
Bee staff writer Mike Mooney can be reached at email@example.com or 578-2384.