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

Life History
Chum salmon return to the Columbia River in late fall (mid-October to December). They
primarily spawn in the lower reaches of rivers, digging redds along the edges of the
mainstem and in tributaries or side channels. Some spawning sites are located in areas
where geothermally-warmed groundwater or mainstem flow upwells through the gravel.
Chum salmon fry emigrate from March through May shortly after emergence in contrast
to other salmonids (e.g., steelhead, coho salmon, and most Chinook salmon), which
usually migrate to sea at a larger size after months or years of freshwater rearing.
Juvenile chum salmon reside in estuaries to feed before beginning a long-distance
oceanic migration. Chum salmon may choose either the upper or lower estuaries
depending on the relative productivity of each. The timing of entry of juvenile chum
salmon into sea water is commonly correlated with the warming of the nearshore waters
and the accompanying plankton blooms (Burgner 1991). The movement offshore
generally coincides with the decline of inshore prey resources and is normally at the time
when the fish has grown to a size that allows them to feed upon neritic organisms and and
avoid predators (Burgner 1991).
Although most juvenile chum salmon migrate rapidly from freshwater to shallow
nearshore marine habitats after emergence from gravel beds, some may remain up to a
year in fresh water in large northern rivers. The period of estuarine residence appears to
be a critical life history phase and may play a major role in determining the size of the
subsequent adult run back to freshwater.
Status and Trends
Columbia River chum salmon were listed as threatened on March 25, 1999, and their
threatened status was reaffirmed on June 28, 2005 (71 FR 37160). Chum salmon in the
Columbia River once numbered in the hundreds of thousands of adults and were reported
in almost every river in the LCR basin. However, by the 1950s most runs disappeared
(Rich 1942; Marr 1943; Fulton 1968). The total number of chum salmon returning to the
Columbia River in the last 50 years has averaged a few thousand per year, with returns
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