A closer look at the wonder of salmon migration

sockeye salmon

Many people know that the broad term “salmon” encompasses several different species. Seven of those are found here in the Pacific Northwest: chinook, coho, chum, pink, sockeye, steelhead and cutthroat. And, within those seven species in Washington state are a whopping 486 distinct populations—each one a scientifically designated, biologically distinct group of individuals (e.g., Lower Columbia River spring chinook; Skagit River coho) adapted to specific streams, estuaries and other conditions.

When people join us for the Cedar River Salmon Journey each October to see salmon spawn, they’re witnessing the journey of a specific group of salmon, through specific conditions that only the Cedar River provides. Because of varying conditions from river to river, each salmon stock has slightly different timing for their reproduction: when they are signaled out in the ocean to return, when they start to move upriver, and when their eggs hatch.

What dictates this timing? What clocks do salmon set their watches by? Thomas P. Quinn explains in his book, The Behavior and Ecology of Pacific Salmon & Trout, “Unlike many freshwater fishes, whose migration and reproduction are strongly influenced by environmental conditions such as temperature, flow or rainfall, in salmon these events are more strongly controlled by genetic factors, as adaptation to the long-term average conditions that prevail in the waters affecting each population. From the ocean, the salmon cannot assess conditions in the river, so selection favors salmon migrating at the right time.” This partly explains why the salmon in the Seattle Aquarium’s exhibits start to mature, even without the environmental cues of the ocean or a river to guide them.

This also explains why it’s so difficult to transplant a population of salmon from one place to another. Their genes determine reproductive timing and, over centuries, those genetics have been honed to a particular stream or river.

One exception to this is the population of Cedar River sockeye. Sockeye are the most numerous salmon to spawn in Cedar River, and this sockeye population was transplanted from Baker Lake stock in the 1930s, after the construction of the Lake Washington ship canal and Ballard Locks. That engineering project lowered the level of Lake Washington by over eight feet and dried up the Cedar River’s natural course of flow to Puget Sound—through the Black River and into the Duwamish. Sockeye salmon were a perfect choice to plant in the Cedar River, which now flowed into Lake Washington, as they are the salmon species whose young rear in a lake before heading out to saltwater.

Cedar river salmon journey

Interested in learning more about salmon migration and salmon in general? Join us for the Cedar River Salmon Journey to talk to trained naturalists while watching salmon spawn! Remaining dates include October 8, 9, 15, 16, 22 and 23 from 11am to 4pm at four locations along the Cedar River in the Renton and Maple Valley areas. Click the link for details!

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