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Medvejie experiment aids accident recovery

SITKA, ALASKA

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Medvejie Hatchery is at the end of a narrow dirt road about 10 miles outside the center of town. It sits inside a secluded cove, where, down in the water, floating metal boardwalks encircle saltwater pens full of salmon.

 

The hatchery is run by the Northern Southeast Regional Aquaculture Assocation, or NSRAA.

 

“It’s probably one of the most complicated Chinook rearing programs in the state,” said Lon Garrison, NSRAA’s operations manager. He says Medvejie produces about 4 million Chinook each year.

 

“About 2 million of those Chinook smolts come from our more traditional program,” he said. “We call that a yearling program. We actually have them on site for longer than a year.”

 

The other two million are called zero-checks.

 

“They may experience a rapid enough growth rate that they meet the minimum threshold to be able to smolt, and go early,” Garrison said. Smolting is the process that makes a salmon be able to move from freshwater into salt water.

 

At Medvejie, zero check smolt come from Green Lake, where the hatchery has some fish pens. The water temperature in the raceways at the hatchery site, where yearlings mature, is between roughly 43 and 46 degrees Fahrenheit. But up in Green Lake, it’s warmer, about 50 to 59 degrees Fahrenheit.

 

“The warmer the water, the quicker the fish can grow. Their metabolism increase,” Garrison said. “We stumbled upon the fact that, in the first couple years as they were feeding those fish, they grew really fast, and we noticed that some of them were smolting. And they were smolting in the middle of the summer.

 

“So, it led us to experiment with a couple of things, and actually take a group, put them in the lake a little early, grow them as fast as we could, and see if we could make them smolt.”

 

And it worked. Now fast forward to the beginning of July. An accidentally closed valve inside one of the hatchery’s on-site raceways resulted in the death of nearly a million young Chinook.

 

The fry that died were yearlings – the Chinook that stay in the fresh water for more than a year. When the accident happened, the zero-check had just been moved into salt water. To replenish the fish in the freshwater raceways, the staff at the hatchery decided to see what would happen if they moved 100 of the zero-check fish out of salt water, and back into fresh water.

 

“If they had all died right within the first few days, we would know that that wasn’t going to be a possibility,” Garrison said. “We had no mortality.”

 

A good sign. So, more fish were sent. Almost a million, using two fish pumps and about 700 feet of pipe and hose.  And now they’re all inside the raceways, six large aluminum tanks, basically, each at waist height off the ground, and a little longer than a semi truck.

 

The zero check fish in the raceways now are about twice the size of the yearlings who were lost, and Garrison says the challenge now will be making sure they don’t outgrow their new surroundings before it’s time to release them.

 

Once they are released, they’ll have a lower survival rate than their yearling cousins.  About 2 percent of yearlings come back, compared to about a half-percent of zero-check. But Garrison said it’s still enough to make the program worthwhile.

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