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Pygmy whitefish are one of four fish species living in Chester Morse Lake.
Pygmy whitefish (Prosopium coulteri) are a member of the Salmonidae family, which also includes salmon, trout, and char. Although widespread in North America during the last ice age, pygmy whitefish now occur primarily in isolated populations that have persisted since glaciers receded over 13,000 years ago.
Pygmy whitefish reach sizes up to 11 inches in length, but average about five to six inches. They feed on zooplankton, crustaceans, insect larvae and pupae, fish eggs, and small mollusks.
Pygmy whitefish spend most of their lives in lakes. Depending on the population, they may spawn in gravels in lakes or in tributary streams from late summer to winter. They are “broadcast spawners” and distribute eggs across the gravel rather than digging a redd, like many fish species. The eggs fall into spaces between gravel where they incubate and hatch.
Currently, pygmy whitefish occur in only nine lakes in Washington state, but are known historically to have occurred in six others. Loss of populations in other lakes is due to use of the pesticide rotenone and the introduction of non-native species.
Pygmy whitefish are not currently listed under the federal Endangered Species Act, but are listed as a state sensitive species by the Washington Department of Fish & Wildlife
The population in Chester Morse Lake is considered to be a “strong-hold” for Washington State according to WDFW, as the fish live in a protected reservoir and are not subject to development or disturbance from fishing or recreation.
The population of pygmy whitefish in Chester Morse Lake was first documented by Keith Wyman in 1975. In the early 1990s, R2 Resource Consultants and SPU conducted studies on the Chester Morse Lake pygmy whitefish population.
A hydroacoustic study in Chester Morse Lake suggests that this species spends most of its time swimming along the contours of the lake bottom. Studies in British Columbia found a similar behavior pattern.
In Chester Morse Lake, pygmy whitefish feed primarily on zooplankton, small clams, and small invertebrates (such as amphipods and chironomids). Pygmy whitefish appear to follow the daily migration of zooplankton in the lake, using the upper parts of the lake during the night and retreating to deep parts in the daytime. Pygmy whitefish are an important food source for bull trout that reside in the lake.
Pygmy whitefish from Chester Morse Lake spawn mostly in the Cedar and Rex rivers. Spawning fish (ranging from one individual to schools of over 1,000 fish) typically begin appearing in the river during the first part of December.
The timing of spawning runs usually coincides with temperatures in the river dropping below 5ºC. Surveys show that pygmy whitefish spawn in the low gradient river habitat just upstream of the lake, which is similar to bull trout spawning areas.
The City has implemented three studies to better understand the ecology of the pygmy whitefish population in Chester Morse Lake and to assess effects of reservoir management on this species.
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Other fish species in the watershed: