Mokelumne River Hatchery Sees Record Return Of Steelhead

By Dan Bacher | January 29, 2017 |

A record run of adult steelhead, 707 so far, has returned to Mokelumne River Fish Hatchery this year, but most of these fish appear to be fish that stayed in the river than going to sea.

“Ninety percent of the fish are adult steelhead in the 18 to 22 inch range averaging 3 pounds each,” said William Smith, hatchery manager. “Most of the fish have summered over in the river, due to the favorable cold water conditions over the past couple of years. We’ve also seen a few larger fish in the 5 to 6 lb. range that have apparently been to the ocean.”

The Mokelumne River below Camanche Dam.
Photo by Dan Bacher.

While the flows haven’t been high in the river over the past couple of years, as they are now, the water temperatures have been favorable, due to the EMBUD’s management of cold water releases from Lake Pardee into Lake Camanche in recent years. “

“Regardless of whether these fish have been to the ocean or not, any of the offspring of these fish have the potential to go to sea,” noted Smith.

The numbers of steelhead returning to the Mokelumne River Fish Hatchery don’t compare to those at Nimbus, Feather and Coleman fish hatcheries in good years, where the fish number in the thousands, but they are a vast improvement over many years when no adult steelhead returned to the facility.

No steelhead came back to the hatchery, located on the river right below Camanche Dam, for 10 years from 1976 through 1986. Again in 1998-1999, no adult steelhead returned to the facility.

That doesn’t mean that there weren’t any rainbows in the river during these years. The river hosted a popular resident trout fishery for fly, bait and lure anglers, but relatively few of the 100,000 steelhead yearlings released every year went to saltwater and returned.

The river, before the listing of the Central Valley steelhead under the Endangered Species Act (ESA), was managed as a catchable trout fishery, rather than as a wild steelhead or trout river. The CDFW regularly stocked the river with catchable size steelhead in the 10 to 15 inch range, hatched from steelhead eggs obtained from the Mokelumne and Nimbus Fish hatcheries.

The river is now managed as a steelhead fishery. Prior to this year, the record for adult steelhead trapped at the facility was 245 fish in 2012. In contrast with this year, 64 adults returned to the facility last year.

Two years ago when I visited the hatchery, the steelhead averaged 4 pounds each and went up to 11 pounds.

This year is the first one hatchery staff are spawning the fish according to a new spawning technique.

“We to maximize the genetic pool, so we take genetic samples of the males and females,” said Smith. “The samples are sent to Santa Cruz for testing. After 3 or four days, we spawn according to the genetics of the fish to insure genetic diversity. We want to avoid spawning related fish to avoid inbreeding.”

Smith attributes the increase in steelhead numbers in recent years to a number of changes in hatchery management that were made possible by the $12.5 million hatchery renovation that was completed in 2002.

First, the hatchery has increased its output of fish from 100,000 yearlings to 250,000 yearlings annually. If you put more fish in the system, more fish are likely to return.

Second, the hatchery has changed the timing of its releases from November and December to February and March, which appears to improve the amount of fish returning.

Third, the hatchery has been releasing the fish at different times and locations based on water conditions in the river. Release locations have included the river below the hatchery, Lake Lodi, the Feist Ranch and New Hope Landing.

“We have been releasing the steelhead on a new moon or during a storm event,” said Smith. “The cover of darkness or highly turbid water helps to reduce predation on the fish.”

Fourth, the hatchery has experimented with releasing steelhead at different sizes, ranging from 4.3 per pound up to 3.5 pounds each, to see which ensure the best survival.

Other factors in the upswing in the steelhead run include the longer time the hatchery staff spends sorting the eggs and the leaving of the ladder open for a longer period of time than before.

Besides hatchery improvements, the construction of new fish passage facilities on the new Woodbridge Dam in the summer of 2006 and the completion of the FERC relicensing process for Camanche Dam in 1999 that provides for increased river flows are responsible for the upswing in the steelhead run.

The California Sportfishing Protection Alliance and Save the Mokelumne River Association played a key role in securing more water for the river from the East Bay Municipal Utility District (EBMUD), increasing the allotment from only 13,000 acre feet in wet years to 85,000 acre feet.

Finally, the “Speece Cone” operated by EBUD at Lake Camanche, a device that distributes oxygen to the lower lake waters at the dam, has also boosted the river’s steelhead and resident rainbow fishery. The device, constructed to improve the quality of water released into the fish hatchery and river in order to stop the fish kills that periodically plagued the river, usually operates from August until mid-to-late October.

While steelhead numbers have increased, the lower Mokelumne continues to offer a quality fishery for resident rainbows. The tail water fishery below Camanche Dam offers good habitat, abundant food and cold water temperatures that keep the fish in the river rather than going to sea.

Fly fishermen, bait fishermen and lure tossers find top-notch trout action during the open season from January 1 through March 31 and the Fourth Saturday in May through October 15. As on other Central Valley steelhead rivers, anglers can only keep one hatchery steelhead and must purchase a steelhead card to fish the river.

The Mokelumne salmon run, as it has on most Central Valley rivers, has ranged from excellent to dismal over the past two decades. A record number of salmon, 16,128, returned to the Mokelumne in 2005.

The total run declined to only 235 fish in 2008/2009, the result of increased water exports from the California Delta to subsidized agribusiness and southern California, low flows below Woodbridge Dam, poor ocean conditions and other factors.

Fortunately the run rebounded over the past several falls. “We saw a close-to-average run in the fall of 2016,” said Smith. “We trapped a total of 6887 fish, including 3,314 adults and 3,573 jacks. That compares to the previous fall’s count of 8,298 salmon, including 5,170 adults and 3,198 grilse.”

Smith noted that a lot of Mokelumne fish went to the Stanislaus, Tuolumne and Merced rivers in the fall of 2016, rather than the Mokelumne, as evidenced by coded wire tag returns from carcass surveys. Twenty-five percent of the hatchery salmon are implanted with coded wire tags.

For more information, call the Mokelumne River Fish Hatchery, (209) 759-3383.