California's chinook salmon may be expanding their territory a bit further south with a so-called "experimental" population newly approved for the San Joaquin River upstream of its confluence with the Merced River, south of Modesto.
The move, announced by the National Marine Fisheries Service (NMFS) in the Federal Register on December 31, may bring spring-run Chinook salmon back to the San Joaquin River system for the first time in more than 60 years. NMFS would likely use spring-run Chinook from Butte Creek, the largest remaining run of spring-run Central Valley Chinook, to repopulate the San Joaquin.
It's a remarkable development for the San Joaquin River, which for decades had so much water diverted from its bed to water crops that it often ran dry for a 60-mile stretch northwest of Fresno.
Chinook salmon, Oncorhynchus tshawytscha, are the world's largest salmon species, with adults generally reaching lengths of two or three feet (though some have been recorded at a whopping 5'10"). They can weight upwards of 50 pounds.
That's a big fish to expect to spawn in a shallow, stagnant river with lots of dry spots; chinook tend to prefer big, broad rivers with lots of water in them. In fact, if it wasn't for a lawsuit launched in 1988 by environmentalists and fisheries groups, reintroducing Chinook salmon into the San Joaquin River would be a fool's errand.
The San Joaquin's spring and fall runs of chinook salmon -- the world's southernmost -- were once so abundant that Central Valley farmers used spawned-out fish as food for livestock. But that changed rapidly in 1942, when the Friant Dam was completed and 4,900-acre Millerton Lake began filling behind it. Built by the U.S. Bureau of Reclamation to supply subsidized irrigation water to farmers in the San Joaquin Valley and Tulare Basin, Friant Dam performed admirably, dewatering 60 miles of the river except in high-water years for about half a century.
As a result of the water diversions, both the spring and fall runs of Chinook in the San Joaquin went extinct in rather short order. That meant the new southernmost limits of the Chinook were in the Merced River. As late as 2005, the San Joaquin was such a death trap for salmon that wildlife managers put an electric fence across the river to make sure salmon from the Merced runs didn't take a wrong turn and get stranded.
In September 2006, though, a settlement in the 18-year-old lawsuit filed in 1988 by more than a dozen environmental and fisheries groups changed things on the San Joaquin. The settlement guaranteed an increasing amount of "restoration flows" allowed to keep the San Joaquin safer for fish throughout the year. In 2009 the operators of Friant Dam started releasing those restoration flows. The releases have ramped up over the intervening years, with the full restoration flows agreed to in the settlement scheduled for this week.
Central Valley spring-run Chinook are listed as threatened under the U.S. Endangered Species Act. As we mentioned earlier, NMFS -- the agency that administers enforcement of the Endangered Species Act for anadromous fish such as salmon -- will consider spring-run Chinook salmon reintroduced to the San Joaquin as a "non-essential, experimental" population. That designation limits liability on the part of irrigators and other land users if their activities end up hurting the salmon. Whether the experimental population will take hold is uncertain. Spring chinook runs in the Central Valley are especially sensitive to drought and a warming climate: lower water and warmer temperatures can mean spawning failures for fish such as salmon and trout that depend on cold water to thrive.
NMFS will see what can be done to reestablish the Chinook regardless, releasing small numbers of fish into the river at first to gauge how well riverbed restoration efforts have performed to restore the once bone-dry San Joaquin for use by salmon.
It's a small step, but it's one that was unthinkable less than ten years ago when the San Joaquin was a dead zone for all things aquatic. A little bit of good news to start the year.