Kodiak hatchery experiments with salt water exposure to mark its pink salmon

Pink salmon swim up a drainage ditch at Beluga Slough on Thursday evening.

Editor’s note: This is the third part of a three-story series about the operations of Alaska’s salmon hatcheries and their consideration in the North Pacific. For the first and second parts, check our July 15 and July 16 editions.

 

Though the pink salmon coming out of Kodiak Regional Aquaculture Association’s hatchery at Kitoi Bay aren’t required to be marked, the managers are looking for ways to do it anyway.

Sheltered from the Gulf of Alaska by the tree-lined shores of Afognak Island in the Kodiak archipelago, the remote Kitoi Bay salmon hatchery is where all the hatchery association’s pink salmon are born. The facility raises and releases four species — pink, chum, coho and sockeye — with pinks being far and away the most populous species in the hatchery.

Researchers and managers often look to otolith marking data to isolate a hatchery fish from wild fish in harvests. However, unlike other hatcheries in the state, Kodiak doesn’t use cycles of hot water and cold water to lay down an otolith mark on its pink salmon. Kodiak Regional Aquaculture Assocition Executive Director Tina Fairbanks said the association does mark its other stocks of salmon, just not the pinks.

“Those requirements have come with production increases over time,” she said. “We have not sought to increase our pink salmon production since that requirement was kind of officially put into place.”

Concern about hatchery pink salmon marking came up in December 2017 in the Homer area when the Alaska Department of Fish and Game released otolith marking data from pink salmon in Lower Cook Inlet streams showing that many of the pinks in those streams were actually Prince William Sound hatchery fish. Because Prince William Sound hatcheries mark their salmon, they’re identifiable from wild stocks, but Kodiak’s pinks would look just like wild stocks.

Otolith marking, called thermal marking, requires hatchery staff to fluctuate the temperature in the tanks where salmon eggs rest over prescribed periods of time. That takes fuel and equipment, which can be expensive. Up till now, Fish and Game managers haven’t indicated a need for it, either, Fairbanks said. Kitoi Bay is relatively isolated from wild stocks and the department hasn’t had concerns about straying, with the bay having direct access to the Gulf of Alaska.

However, Kodiak Regional Aquaculture Association is looking at other ways of marking that could make it economically viable, she said.

“When I heard that one of the labs in Southeast … was doing some new research, I looked into it a little bit more and through a variety of discussions, they indicated they had been doing some salt water marking,” she said.

Kitoi Bay uses salt water already, pumping it through some of the egg incubators to help purge fungal infections. In the past, hatchery staff sent in some samples from Kitoi Bay fish to see if the salt water had an impact on the otolith, but Fish and Game staff couldn’t discern the mark from that exposure, so the hatchery abandoned that idea.

But last year, the hatchery staff tried something new — exposing eggs to a longer period with salt water with full strength to see if the eggs would both survive and have a readable otolith mark. The results were good — with a 12-hour exposure length, the eggs appeared to have a 100 percent survival, Fairbanks said. The hatchery is planning to watch the returns for the pink salmon that were exposed to the salt water to evaluate their adult survival, but preliminarily, the results are promising, she said.

“We’re pretty thrilled to be both achieving a mass mark for Kitoi Bay pink salmon and finding a way to do it cost-effectively,” she said.

The marking idea came from John Holt, a researcher with the Southern Southeast Regional Aquaculture Association. Kitoi Bay’s equipment was good enough to try the salt water marking without making any changes, he said.

“They had the ability already to just try to do the marks with salt water,” he said.

“That’s really the goal, (that) they are distinct.”

The salt water marking is just part of the research that Holt and Susan Doherty, who formerly directed research programming at SSRAA, are working on related to otolith marking. The two started a company called Otolith Marking and Reading Research to look into micromarking — marking processes that would be cheaper and take less time. Though the research is ongoing, some of the trials have shown readable results with much shorter periods of temperature change than previously thought.

“The minimum was believed to be 12 hours of a thermal change to create the mark,” Holt said. “We thought we’d just be able to create a pattern that might not be discernable by the human eye but we could create a computer vision by software that could read it … What we found is that as little as an hour of thermal change can create a distinct ring.”

Though the results are promising, the trouble is finding a way to read them effectively. Currently, otoliths are ground down and examined under a microscope to read the marks. The micromarks would need imaging software to read, Holt said.

There are other ways to leave marks — the preservative formalin, for example, leaves a mark — but one thing Holt said he is interested in is developing a way to read innate marks. Even wild salmon have marks on their otoliths from the stresses of their lives, such as transitioning from eating the yolk in an egg sac to exterior sources. Holt said that it may not be possible to identify wild fish by their otoliths through otolith marks alone, but in tandem with statistical evaluation, it could be possible in the future.

“Some of these systems are so long and have so many different spawning grounds in them that it would be hard to find something common to all the fish migrating out, to say this is that signature,” he said. “It might be something that happens as they all transit through estuarine waters, that leaves a mark on the otolith. The other thing is I would not expect it to be a discernable pattern — again, it’s a statistical approach.”

Reach Elizabeth Earl at eearl@peninsulaclarion.com.

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