Agriculture

Study questions Stanislaus releases for salmon in fall

Jacque Demko and Spencer Callahan clear the weir of debris and algae on the Stanislaus River, about a mile from Jacob Myers Park, in December 2010.
Jacque Demko and Spencer Callahan clear the weir of debris and algae on the Stanislaus River, about a mile from Jacob Myers Park, in December 2010. Modesto Bee file

A new study concludes that salmon have not benefited much from autumn water releases into the lower Stanislaus River.

The research by the Fishbio consulting firm backs up claims by the Oakdale and South San Joaquin irrigation districts that the October releases are wasting water from New Melones Reservoir.

The “pulse flows” are done on San Joaquin River tributaries with the aim of getting adult salmon to spawning areas after a few years in the Pacific Ocean. They are not directly related to the current state proposal to boost flows even more from February through June to help the young fish out to sea.

Fishbio, based in Oakdale, analyzed salmon counts just downstream of Riverbank from 2003 to 2014 that were funded by OID and SSJID. It found that higher fish numbers correlated with higher flows in just two of those years. It suggests limiting the pulses to 700 cubic feet per second, about half of what was done during the study period.

That lower level would mimic conditions on the Stanislaus before it was dammed, study co-author Doug Demko said Thursday.

“When they are migrating back from September to November, it’s a time when the rivers are typically low,” said Demko, the firm’s president.

The study found that the salmon are better served by a temporary barrier that can be placed across the entrance to the Old River, a channel near Tracy that leads to massive fish-killing pumps in the Sacramento-San Joaquin Delta.

The National Marine Fisheries Service, which helps manage salmon, issued a brief statement on the Fishbio report from its Sacramento office: “We are aware of the pulse flow report but have not yet had the opportunity to fully evaluate its analysis and findings.”

Fisheries ecologist Tom Cannon, an advisory board member for the California Sportfishing Protection Alliance, said the most important factor for spawning is water temperatures of 60 degrees or lower. The releases from New Melones should be at whatever volume achieves that, he said.

The reservoir is designed to provide this cooler water from an outlet near its bottom. Storage in recent years has been so low at times that the water got too warm.

The pulse flows in the study were done for about two weeks each October and increased in 2009 to comply with new federal rules for fish. The Tuolumne and Merced rivers also have had fall releases, but at a lower level.

Demko and co-authors Matthew Peterson and Andrea Fuller published the study in the North American Journal of Fisheries Management.

“We need to know our river a bit more,” SSJID General Manager Peter Rietkerk said Thursday. “We need to understand what is actually causing migration, what is causing a beneficial outcome for salmon.”

A video from Fishbio is at https://www.youtube.com/watch?v=kRUU1PIZAec.

John Holland: 209-578-2385

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