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

all three a.i.s are expected to be applied to several crops within the ESU. Agriculture activity is
prominent in the lower Sacramento River and within the Delta. Chinook salmon are also
exposed to poor water quality from agricultural runoff that enters the Delta from the San Joaquin
River. The Mediterranean climate in California, with dry summers and fall storms, may result in
high concentration of these contaminants in run-off during the onset of the rainy season. These
high concentrations can overlap with juvenile presence in the river system and movement into
floodplains for rearing.
Winter-run adults enter the Sacramento River in early spring with spawning peaking in May and
June. Spawning occurs in the Sacramento River downstream of the Keswick Dam. Fry rear in
the Sacramento River for a few weeks to months before starting outmigration in late July,
peaking in November and December. During outmigration, the young salmon migrate down the
Sacramento River, through the Delta and San Francisco Bay. Juvenile winter-run Chinook
salmon appear in the Delta from October to early May where they may rear in the fresher
upstream portions for up to two months.
We expect that the proposed uses of carbaryl, carbofuran, and methomyl pesticide products will
lead to both individual fitness level and subsequent population-level consequences. Registered
uses of these a.i.s indicate overlap with the spawning, rearing, and migratory habitat of the one
extant population in this ESU. Thus, the risk to this species’ survival and recovery from the
stressors of the proposed action is high for carbaryl, carbofuran, and methomyl.
Snake River Fall­run Chinook salmon
The SR Fall-run Chinook salmon ESU is comprised of a single population that spawns and rears
in the mainstem Snake River and its tributaries below Hells Canyon Dam. Only 10 to 15% of
the historical range of this ESU remains. Estimated historical returns from 1938 to 1949 were
72,000 fish annually (Bjornn and Horner 1980). The average abundance (1,273) of SR Fall-run
Chinook salmon over the most recent 10-year period is below the 3,000 natural spawner average
abundance thresholds identified as a minimum for recovery. The annual population growth rate
for this single population is 1.02. Two historical populations are considered extirpated.
445