Ill-timed releases from New Melones Reservoir led to a 75 percent drop in rainbow trout on the lower Stanislaus River last year, according to two water purveyors that could have used some of the supply.
The Oakdale and South San Joaquin irrigation districts contend that the water was too warm for the fish because of the much-reduced level of the reservoir. They also claim that large releases in general do little good for the trout or chinook salmon.
A spokesman for the U.S. Bureau of Reclamation, which manages New Melones, said the low level was the result of a severe drought and the competing demands on the reservoir.
The issue involves rainbow trout that spend their entire lives in the river stretch between Goodwin Dam, just below New Melones, and the confluence with the San Joaquin River. Rainbows also can become steelhead, an oceangoing fish listed as threatened under the federal Endangered Species Act. Water suppliers have faced cutbacks to protect steelhead, as well as salmon, which also spend part of their lives at sea.
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The rainbow trout survey was conducted by Fishbio, a consulting firm with an office in Oakdale. The river averaged a healthy 20,000 or so fish from 2009 to 2014, but the count dropped to about 5,000 last year because of the warm water, Fishbio President Doug Demko said. The river got as warm as 69 degrees, the highest temperature since 1998, Fishbio reported.
All the pulse flows are really doing is using stored water in the reservoir.
Doug Demko, fishery consultant
Demko talked about the issue last week at Knights Ferry, where a Fishbio crew was conducting the 2016 trout survey. Employees donned snorkeling gear to look for rainbows and other species in the hip-deep water.
Demko said many people assume that large reservoir releases benefit the fish in the river below, but water temperature is more important. He prefers to hold back more water in New Melones, allowing it to maintain the cold reserve at its bottom that would aid the fish later.
“All the pulse flows are really doing is using stored water in the reservoir,” Demko said.
OID and SSJID have fared relatively well during the five-year drought, thanks to water rights that give them first call on the New Melones storage. But they have raised concerns that releases for lower-river fish have reduced their carryover supply at the end of each irrigation season.
Bureau spokesman Shane Hunt said the Stanislaus is “overallocated” for irrigation, fisheries and other uses even in wetter times, and the dry conditions since 2012 have made things worse.
“Most of the native species up and down the (Central) Valley and in the Delta have been pretty hammered by the drought,” he said.
The bureau manages Stanislaus flows under a “biological opinion” adopted in 2009 to protect the fish, Hunt said. Those procedures, spelled out by the National Marine Fisheries Service, will soon be reviewed to see how they could be improved, he said.
Conservation groups have urged higher flows to balance what they see as too-heavy water use by farms. This is a part of river management that should extend from the upper mountains to the coast, said Mark Drew, director of the Sierra headwaters project for California Trout.
He also noted the extended dry conditions.
“The reality is the drought has been profound and its impacts are continuing,” he said.
John Holland: 209-578-2385