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Carbaryl, Carbofuran, and Methomyl - National Marine Fisheries ...

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of historic spawning areas. Additionally, alteration of the Lower SR by hydroelectric<br />

dams has created a series of low-velocity pools in the SR that did not exist historically.<br />

Life History<br />

Prior to alteration of the SR basin by dams, fall Chinook salmon exhibited a largely<br />

ocean-type life history, where they migrated downstream <strong>and</strong> reared in the mainstem SR<br />

during their first year. Today, fall Chinook salmon in the SR Basin exhibit one of two<br />

life histories: ocean-type <strong>and</strong> reservoir-type (Connor, Sneva et al. 2005). The reservoirtype<br />

life history is one where juveniles overwinter in the pools created by the dams, prior<br />

to migrating out of the SR. The reservoir-type life history is likely a response to early<br />

development in cooler temperatures which prevents juveniles from reaching suitable size<br />

to migrate out of the SR.<br />

Adult SR fall-run Chinook salmon enter the Columbia River in July <strong>and</strong> August.<br />

Spawning occurs from October through November. Juveniles emerge from gravels in<br />

March <strong>and</strong> April of the following year, moving downstream from natal spawning <strong>and</strong><br />

early rearing areas from June through early fall.<br />

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