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NW Fishletter #376, December 4, 2017

[4] Mystery of Poor Survival of Sockeye Smolts May Be Solved

The different water chemistry at the Springfield hatchery and in Redfish Lake Creek likely explains the smolt mortality seen in 2015, 2016 and 2017, and points to possible solutions, according to a presentation given to the Northwest Power and Conservation Council Nov. 14.

When Idaho Department of Fish and Game completed the Springfield sockeye hatchery in 2013, the agency expected 5,000 adult sockeye would eventually return to Lower Granite Dam from the ramped-up production and release of juveniles.

Instead biologists observed higher than usual mortality after the first batch of juvenile fish were transported from the hatchery to the release site at Redfish Lake Creek.

Funded by BPA as part of the Snake River Sockeye Salmon Recovery Program, the Springfield Fish Hatchery's objective is to produce a million sockeye smolts (juvenile salmonids). This number of juveniles could result in the eventual return of several thousand more adult sockeye than the 3,000 highest adult returns from the program, which started in the mid-1990s.

The hatchery is operating as anticipated and producing high-quality smolts, Paul Kline, IDFG's Assistant Chief of Fisheries, told the Council.

But within two days of the first release of juvenile sockeye in 2015 to Redfish Lake Creek--a four-to-five hour drive from the Springfield hatchery--biologists sampling juveniles at Lower Granite Dam found thousands of dead smolts and others in poor condition.

In 2015, "poor condition" included signs of gas bubble disease and blunt force trauma in the juvenile sockeye. Was it a faulty aerator? A problem while loading smolts into thetransport truck? IDFG addressed the gas super-saturation issue and acquired a larger fish-loading pump.

In addition, IDFG personnel analyzed the program's protocols for rearing, loading, hauling and release.

Still, survival did not improve in the smolt releases of 2016 and 2017.

value
A few sockeye still spawn in Little Redfish Lake. Credit: Wikipedia User Fredlyfish4

In 2016 high descaling was observed at release, and smolt readiness was suspected, Kline told the Council. Release timing was moved up by two weeks.

With no improvement in survival again this year, other factors were likely responsible, he said.

Dr. Jesse Trushenski, IDFG Fish Health Program Supervisor, was called in.

Working with NOAA Fisheries, staff from the two agencies evaluated the last six months of smolt rearing and releases "in case there was something we had overlooked," Trushenski said at the Council meeting.

This additional work involved physiological measures of two interrelated processes in salmonids--smoltification, which is the physiological transformation needed to adapt to saltwater; and the stress response.

Examining blood and gill tissues, the scientists found high levels of cortisol and glucose before and after transport.

High levels of the stress hormone cortisol and of the energy-supporting compound glucose are normal for juvenile fish being pumped into a crowded tank and transported, and normal for juvenile salmonids going through smoltification.

After the juveniles have been released, "we might expect the smolts to start recovering, but instead we saw a sharp uptick in cortisol and glucose levels," Trushenski said. Even after 24 hours, the degree of recovery was weak.

She said this suggested the fish were encountering a serious stressor after release.

The scientists started looking for possible causes and discovered major differences in water chemistry between Springfield Hatchery and Redfish Lake Creek.

"Turns out, the well water at Springfield is very hard--high in calcium concentrates--and has high alkalinity, while Redfish Lake Creek is practically distilled water," the fish health expert said. The creek water is unusually soft and has low alkalinity and generally a lower pH than the Springfield water.

Dramatic differences in water chemistry like this can cause disease and mortality in salmonids, especially combined with a stressor such as smoltification.

Trushenski said the discrepancies in water chemistry appear to be the smoking gun in the significantly reduced survival of Springfield-reared smolts.

What's the solution? So far, the short-term holding of sockeye smolts at another facility with a different water source prior to release into Redfish Lake Creek holds the most promise, according to preliminary results of a multi-phased experiment started this fall and conducted by Trushenski.

The other facility is the Sawtooth Hatchery, also part of the Snake River Sockeye Salmon Recovery Program, but with water from the Salmon River, which has water chemistry values intermediate between the Springfield Hatchery and Redfish Lake Creek.

Experimentation will continue in spring 2018. The presentation at the Nov. 14 Council meeting tells more about the puzzle and the research underway to address sockeye smolt survival.

BPA has faith that the problem will be resolved. "We are confident that our partners will find a solution to the Springfield Hatchery issue," Bonneville spokesman David Wilson told NW Fishletter. "We feel it is still very much a viable hatchery for salmon and a good use of ratepayer dollars," he said.

"It's good to remember that it's hatcheries similar to this that likely saved Snake River sockeye from extinction." -Laura Berg

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Publisher/Editor-in-Chief: Mark Ohrenschall, Editor: Laura Berg
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