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Threat of disease prompts early release at Sitka hatchery

A crow enjoys a fat coho smolt. Garrison says that the smolt were being reared for a second year, in the hope of improving subsequent runs. (KCAW photo/Rich McClear)

A crow enjoys a fat coho smolt. Garrison says that the smolt were being reared for a second year, in the hope of improving subsequent runs. (KCAW photo/Rich McClear)

The Sitka Sound Science center prematurely released some coho salmon smolt this month, in order to prevent the spread of infection throughout its hatchery. The hatchery’s water supply – which is fed by the nearby Indian River – was compromised by the huge numbers of dying pink salmon this fall.

The release created a minor feeding frenzy on Sitka’s waterfront, as birds and other predators descended on the smolt. KCAW’s Rich McClear stopped by the Science Center to check on the commotion, and to learn more about the unusual timing of the salmon release.

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There was a congregation of birds — gulls, ravens, crows and even a heron — all around the outflow of the Science Center hatchery. I saw one raven holding what looked to me like a baby salmon. But salmon are released in the spring. What was happening? I went into the science center to find out. A worker there told me they had just released thousands of smolt, or baby salmon. But why? The next day I found Lon Garrison, Aquaculture director for Sitka Sound Science Center.

“We recently had to release some smolt we tried to hold on to for a second year and release as two year olds. And we had to let those go because they were developing some health issues with a naturally occurring disease called Bacterial Kidney Disease. The Indian River system has Bacterial Kidney Disease in it as a natural pathogen.”

The hatchery was trying to hold on to the smolt for an extra year because the summer’s weak return of coho did not produce enough eggs for next spring. Garrison hoped that by releasing these baby fish in the spring of 2014, it would improve subsequent runs. But that didn’t work as well as he had hoped. Bacterial Kidney Disease – or BKD — exists all along the west coast but this was a particularly bad year for Indian River, in part because it was such a good summer.

“This year we’ve actually had some of the worst water quality that I’ve seen coming into any hatchery. The water for the SJ hatchery comes directly from Indian River and, of course, this year Indian River had a phenomenal return of pink salmon. Probably somewhere between 300 and 400 thousand pink salmon returned, which is close to 3 or 4 times what the escapement goal would be. So we were well over what we should have had. So what that translated to this year, especially with a low water year where we didn’t have a lot of rain, we ended up with a tremendous biomass in the river and they were using up oxygen like crazy. So the dissolved oxygen in the water that was coming to the hatchery was the lowers I have ever seen.”

The low oxygen level weakened the fishes’ immune systems; the huge numbers of dying fish introduced unusual amounts of fungus and bacteria into the hatchery’s water supply. Unwilling to consider antibiotics, Garrison decided to release the fish before the bacteria spread throughout the rearing pens.

“When those fish are reared in an intense situation like they are in a hatchery the mortality can just continue to increase so the best course of action is to let those guys go and so they got an early release, November is not a general time we try to release fish. Obviously there’s not a lot of food left in the ocean at that time and there’s a lot of predators around at the end of the season so we normally like to release those fish in the spring, but we had to do it a little earlier than we had planned.”

So does that mean that these smolt are a loss? Garrison doesn’t necessarily think so.

“I’m still hopeful that we’ll still see some coho come back, even from this release, I mean the majority of the fish were very healthy, they were a good size, nearly twice the size of the fish released in the spring. They were pretty chubby so they have a lot of energy reserves so I think if they can escape the predators and they didn’t come down with the kidney disease, they probably should do just fine.”

That was Lon Garrison, aquiculture director for the Sitka Sound Science Center. Garrison says now that the fish are released they will disinfect their pens with bleach and try again next year.

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