Examination of salmon scales may determine age

By Jenny Neyman
Redoubt Reporter
If only salmon could talk. Biologists could solve some of the age-old mysteries about these wild, wily creatures, and answer questions regarding Alaska king salmon that have become increasingly worrisome in recent years.
It might go something like this:
How you been? Back so soon? Been getting enough to eat?
In a way, salmon can talk, at least so far as communicating information about themselves. It just takes a trained eye, rather than ear, to “listen.” And a fish scale, rather than mouth, to “speak.”
A single scale can say a lot about a salmon — its age, its growth patterns, its general life history. Similar to how a tree can be aged by counting its rings, calcified structures in fish, such as their scales and otoliths (ear bones), develop tiny rings, called circulai, that correspond to the growth of the animal. “Reading” the patterns of circulai and spaces between them can reveal information about a fish — did it grow a lot when it was out to sea? Did it survive some kind of injury or other limitation on its health? How many years did it spend in the ocean before returning to its natal stream to spawn?

Photo by Jenny Neyman/Redoubt Reporter - Eskelin loads three scale cads, covered with a layer of acetate, into a scale press at the Fish and Game office in Soldotna. The machine presses and heats the scales, so that an impression is made in the acetate. The acetate then can be examined, while the scale are filed away in storage.

Photo by Jenny Neyman/Redoubt Reporter -
Eskelin loads three scale cads, covered with a layer of acetate, into a scale press at the Fish and Game office in Soldotna. The machine presses and heats the scales, so that an impression is made in the acetate. The acetate then can be examined, while the scale are filed away in storage.

The method for doing so is intricately precise, yet has a bit of a mystical feel, sort of like if biologists set up a tea leaf-reading booth at a science fair.
“Do you see it? Concentrate right in here. You can zoom out if you need to, that helps sometimes. The other trick is to step back and all of a sudden, ‘Oh, I can see the lines,” said Tony Eskelin, fisheries biologist in the Soldotna office of the Alaska Department of Fish and Game. Eskelin headed the sampling project of king salmon harvested in the East-side Cook Inlet commercial set-net fishery this summer, meaning he had the task of aging hundreds of scales this fall. As with most nonintuitive processes, practice makes more proficient.
“I got a lot better after the, oh, 600 I did,” he said. “There are little things you can do to see them better.”
The idea of mining calcified structures for biological information is an old one — scientists first started examining fish scale patterns as a means to identify different groups of fish in the early 1900s. The standard technology used isn’t exactly going to set a Silicone Valley tech conference on fire, either. Sampled scales are affixed concave side up — like a contact lens — to scale cards marked with a grid three tall by 10 wide, accommodating three scales each from 10 fish. The cards are then pressed onto clear acetate sheets to make impressions of the scales, so the patterns can be examined while the scale cards themselves are filed into storage.
The scale press looks like a cross between an industrial drill press and an Easy-Bake Oven. The scale cards are covered with precut acetate sheets and placed on a metal tray, which is fed into a slot between two plates in the press. Pumping a lever brings the plates together, with a dial showing the force of pressure. Another gauge shows the temperature. There’s a specific recipe to be followed.
“It needs to get up to 2,500, at least, pounds of pressure for two minutes, at least 190 degrees,” Eskelin said.
When the cards are pressed they’re removed — hot, use gloves — and examined to make sure the impressions are clear. If not, they’re repressed. If they’re good, the cards are ready to be examined. On to hulking technological relic No. 2 — a microfiche reader, the kind used in libraries to examine film of old newspaper clippings.
They might not be on the hot list at Best Buy this Christmas, but the machines are still used because they still work great for this task, said Wendy Gist, fisheries biologist in the Soldotna office, whose task this year was aging scales taken from sockeye salmon sampling.
“It’s kind of funny we use these old-fashioned machines. But I’ve done so much research because I’ve wanted to update to keep up with technology, but nothing works like this,” Gist said.
the microfiche is loaded, the science the science of scale reading becomes a little more of an art form. The methods of examining scales have been refined and standardized, sometimes minutely enough for one stock of salmon versus another, but there’s definitely an acquired knack to telling one clump of teeny-tiny wiggly lines from another clump of teeny-tiny wiggly lines.
That’s what the examiner looks for — bands of concentric circles radiating out from the focus — the line where the scale was attached to the fish. The distances between the circulai indicate how rapidly a fish has grown. Closer-together lines indicate a period of slower growth, which generally means wintertime, when feeding conditions aren’t as good. That’s a winter check. Bands with farther-apart circulai indicate a period of rapid growth, which generally occurs in the summer.
“You see a summer here, where it’s a little bit wider spaced — that’s better feeding, typically. Different feeding patterns are what create this pattern,” Gist said.
She’s also a proponent of the zoom in, zoom out method of adjusting magnification. Some scales are more easily read at a higher power, some lower, she said. If that isn’t enough, she’ll try moving her head to vary at what angle she’s looking at the screen.
“You know those Magic Eye pictures? (Books and posters where viewers try to see three-dimensional images from two-dimensional printed patterns, popular in the 1990s). You get your eye in the right line and you can see it. This reminds me of that,” Gist said.
The first big change in circulai, nested in closest to the focus, indicates when a smolt left its natal stream and headed out to sea, since, before that point, young salmon don’t grow by huge amounts.
After that, the bands show seasons — tighter bands for winters, wider bands for summers.
“When you hit saltwater, your goal is to put on as much as you can,” Eskelin said.
The last band of wider-apart circulai under
a biologist’s examination is usually
truncated — just as the salmon’s life

was. Death makes for an abrupt limitation on growth.
“The last summer is just this little bit,” Eskelin said, pointing to a thin band of wider-spaced circulai on the outer edge of the scale. “Because it started growing in April and got caught in July.”
Counting the checks shows the age of the fish. A one-ocean fish would be a salmon that spent only one year in saltwater before returning to spawn. A two-ocean fish spent two years in saltwater, and so on. Most Kenai Peninsula king salmon spend one year in fresh water, then migrate to the ocean when they are about 4 inches long. How long a salmon spends in saltwater, how much it eats while in the nutrient-rich ocean, and its genetic makeup all contribute to how big it ultimately grows (kings from the Kenai River are generally larger than those from the Kasilof, for instance).
Some kings return to spawn after only one year in saltwater — generally fertile males that haven’t grown very big. Others come back after only two years at sea, again usually males, weighing about 10 to 20 pounds. The majority of Southcentral kings return after three and four years at sea, weighing 25 to 60 pounds.
But the scales sometimes can be deceiving.
There can be breaks in the circulai lines, making them hard to read. Or there can be false checks, a band of close-together circulai indicating a period of slow growth from something other than the doldrums of winter.
“There could be several reasons, like it had an injury,” Gist said. “It’s something that’s messed up its growth.”
Some scales are ripped off from injury and regenerate, so they no longer provide a true record of growth and age. That’s why three scales are taken from every salmon sampled, to increase the odds that at least one will be readable.
If visual examination isn’t clear, there are backup methods to gauge age. Though laborious, counting the circulai can help, since there generally are a consistent number of circulai put on each winter and summer. Ages from scales can also be referenced to the length of the fish, which also is recorded when the scale samples are taken. Occasionally scale agers hit the jackpot — a fish marked as a juvenile with a coded wire tag, so they know exactly how old it is. That offers an opportunity to test scale examination prowess.
“You know what it is, so let’s do a blind test here and see, how did you do?” Eskelin said.
There are others with experience in the office who can lend an eye to a difficult scale, or can serve as a periodic check to make sure scale estimates are on target. To neophytes staring at their first Magic Eye pattern of a magnified scale, the task can seem daunting. But with experience comes accuracy. Gist said that when she was training to age scales the target of accuracy was 90 percent. Eskelin said his goal is at least 95 percent.
Accuracy is particularly important, given that the information isn’t just idle knowledge. Age, sex and length data is used to construct brood tables. And along with abundance estimates, composition data of a run helps biologists estimate future runs. It’s also helpful in discerning trends over time.
“It tells us a lot about patterns, fishing numbers, how the management strategies are working. It’s not all black and white, but they’re always looking at numbers. If there’s a really strange year they’re going to analyze that, ‘OK, is there something really strange going on here, or is it just a cyclical thing?’ They’re looking at all sorts of possibilities,” Gist said.
For instance, king sizes in the Kenai have seen a downward trend over the years. Does that mean the fish are returning when younger and, thus, smaller? Or are today’s spawners roughly as old when they return as they have been decades ago, but just haven’t grown as big as they used to — indicating, perhaps, something awry with the productivity of their ocean environment?
With state funding through the Chinook Salmon Research Initiative to investigate why the state’s king runs have been dwindling in recent years, the more global implications of these questions could receive additional attention.
Collecting and aging scales on stocks for which escapement is tracked is nothing new for Fish and Game. Regional offices use the data to construct brood tables and help estimate future runs. But one project funded through the research initiative calls for identifying 12 indicator stocks of king salmon around the state and creating a database of information for those indicator stocks for as far back as regional Alaska Department of Fish and Game offices have it.
The Kenai River is designated as one of 12 indicator king salmon stocks in the state, along with the Unuk, Stikine, Taku, Chilkat, Copper, Susitna, Karluck, Chignik, Nushagak, Kuskokwim and Yukon rivers. So the Soldotna office sent its king scale data to Juneau for as far back as it goes — about 50,000 scales, Eskelin said, dating back to 1986.
At this point the goal is to just amass the information in one place.
“It’s common for us to be not just counting fish, but to be getting a sample of that escapement so we can characterize what the age structure of that escapement is. It’s a very common thing for us to do and we have a lot of this information already ongoing for some of these indicator stocks. We just want to make sure whatever information we collect, we continue to get the age, sex and length information to go with it. It’s pretty much what’s been going on for a long time, but if we were going to institute any new projects we just want to make sure that’s included,” said Eric Volk, scientist with Fish and Game in Juneau.
Potentially, that data could be useful in studying if something is going awry in the ocean environment that is affecting king returns.
“There’s a lot of published and anecdotal information that suggests that fish — not just Chinook, but other species, too, like chum salmon — that it’s possible that the maturity schedules are changing, and we’re actually experiencing fish returning smaller at age and perhaps younger in the return overall. If you thought that maybe food was in shorter supply out in the ocean, you might start to see fish coming back at smaller sizes or younger ages. We don’t really know that that’s happening, but it’s a possibility, so understanding how big fish are and how old fish are when they come back is a pretty important question,” Volk said.
“And it feeds into what a lot of people are talking about in ‘quality of escapement,’ like maybe you’re making the numbers of escapements, but we would want to know whether or not a lot of those numbers were much smaller fish. We want to be aware of any changes that are occurring in the size and age structure of that escapement.”
The nature of a fish run is measured in more than just how many fish return, it’s how big and how old those fish are, and the ratio of males to females.
“There’s a lot of folks who would encourage people to look more at escapements in terms of what those escapements really look like, beyond just counting numbers of fish. So that’s where (ASL data) comes into play. It’s just fundamental biological information — how old and how big are fish in the return, either in the catch or in the escapement. So there may be any number of questions you may be asking with that kind of fundamental information. It’s foundational information for population demographics — how old are those fish, how big are those fish — so scales are really important for salmon because that’s the easy and efficient way of aging fish.”

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Posted by on Oct 22nd, 2013 and filed under Headline News. You can follow any responses to this entry through the RSS 2.0. Both comments and pings are currently closed.

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