Nuu-chah-nulth women study salmon mysteries

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In a tiny lab surrounded by microscopes and boxes upon boxes of slides, Judy Joseph (Ditidaht) and Susan Cootes (Uchucklesaht) are helping scientists answer some of the most perplexing questions in salmonid science.

Before hatchery raised salmon fry are released into the wild, hatchery personnel manipulate the water temperature in the hatchery tanks. The temperature fluctuation causes a mark to appear on the salmon's ear bone, also called an otolith. Each hatchery on the west coast of North America has it's own specific degree of temperature fluctuation, which causes their fish to have a very specific thermal mark on their otolith.

When a commercial or recreational fisherman catches a hatchery-raised salmon (identified as having its adipose fin clipped) they are to give the head of the fish to the Department of Fisheries and Oceans for analysis and identification. This is where Judy and Susan come in.

Inside their laboratory at the Robertson Creek Fish Hatchery near Port Alberni, the pair dissects thousands and thousands of fish heads each year to analyze the otolith bones. They find the bone, carve it out, and grind it down to a paper-thin cross-section they can put on a glass slide and study through powerful microscopes. The layers, or rings of the bone are much like rings of a tree, telling scientists how old the fish is and whether it enjoyed bountiful years or lean years with little food. The cross-section also contains the thermal mark, allowing Judy and Susan to determine which hatchery raised and released the fish.

"The information we gather here is used to study fish movements up and down the coast, and also to explore issues around hatchery and wild fish," said Susan.

"The data we collect here is combined with all kinds of other data like creel surveys, ocean productivity and temperature patterns and stomach content studies to gain a better understanding of how hatchery salmon interact with and compete with wild salmon," she said.

The otolith marking program has been operating in Canada for the past 10 years, and in the United States for the past 20 years.

The data gathered by Judy and Susan is sent to the Pacific Biological Station in Nanaimo where it is used in countless studies.