The Port Gamble S’Klallam Tribe is studying how low dissolved oxygen (DO) levels affect salmon egg development.

The tribe took 18 adult female chum salmon that returned to the tribe’s Little Boston hatchery this past fall and exposed groups of them to tanks of fresh water with various DO levels.

One group of fish was exposed to 10 milligrams of DO per liter of water, representing the preferred water conditions for healthy streams around Hood Canal. A second group was exposed to 2 milligrams of DO per liter and a third group was exposed to 3 milligrams of DO per liter. Each group was exposed in its assigned tank for 36 hours.

“The brief exposure mimics when fish swim through Hood Canal during a low DO event, versus a chronic exposure, when they’re in a low DO situation and can’t swim away,” said Hans Daubenberger, the tribe’s senior research scientist.

The 2 and 3 milligram levels are what fish may encounter during a low DO event or while in a low-flow stream during the summer, he said.

Following exposure, the salmon were spawned and incubated in the tribe’s hatchery. Daubenberger and his staff will evaluate the development of the eggs over the winter as they mature.

The primary indicator is expected to be significant egg mortality, he said, but if that isn’t apparent, then they’ll observe the physical development of the fish.

The experiment is two-fold: to assess climate change impacts and fisheries management techniques.

“With climate change, we expect to see warmer water temperatures in the near future, which causes low DO,” he said. “It’s an inverse relationship – as water temperatures increase, the maximum saturation of dissolved oxygen in water decreases.”

Because fisheries managers survey creeks for egg nests as a way to determine fish populations, it would be helpful for them to know if the eggs are dying because of low dissolved oxygen, he said.

Port Gamble S’Klallam Tribe biologists measure a female chum salmon whose eggs were used in a study to see how eggs are developmentally affected after being exposed to low dissolved oxygen levels. Photo: T. Royal