By Jenny Neyman
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 circuli, that correspond to the growth of the animal. “Reading” the patterns of circuli 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?
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 25,000 PSI for two minutes, at 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.
Once 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 circuli 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 circuli 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.