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

1994). Most juvenile steelhead spend two or three years in freshwater before migrating to the
ocean. Some juvenile steelhead may spend up to seven years rearing in freshwater before
migrating to sea. Given the long duration in shallow freshwater habitats, juveniles are more
likely to experience higher pesticide exposure, contaminants, and elevated temperature.
We expect that the proposed uses of carbaryl, carbofuran, and methomyl may contaminate the
rearing habitat of UCR steelhead and lead to individual fitness and population-level effects.
Therefore, the risk to this species’ survival and recovery from the stressors of the action is high
for carbaryl, carbofuran, and methomyl.
Upper Willamette River Steelhead
The UWR steelhead DPS includes all naturally spawned late-fall populations below natural and
man-made impassable barriers in the Willamette River, Oregon, and its tributaries upstream from
Willamette Falls to the Calapooia River. The DPS is comprised of four historical populations.
Steelhead populations within this DPS have been declining, on average, since 1971 and have
exhibited large fluctuations in abundance. Long-term trends in the annual population growth rate
are less than one. The annual population growth rate of the four independent populations ranged
from 0.97 to 1.023.
The major threats to this ESU identified in the Status of Listed Resources and Environmental
Baseline sections include habitat loss due to blockages from hydroelectric dams and irrigation
diversions, and degraded water quality within the Willamette mainstem and the lower reaches of
its tributaries. Additionally, pesticide use and detections in UWR steelhead freshwater habitats
are well documented. Fifty pesticides were detected in streams that drain both agricultural and
urban areas. Forty-nine pesticides were detected in streams draining agricultural land, while 25
pesticides were detected in streams draining urban areas. Ten of these pesticides, including
carbaryl and carbofuran, exceeded EPA criteria for the protection of freshwater aquatic life for
chronic toxicity (Wentz, Bonn et al. 1998). The combined impacts from these multiple threats
continue to affect UWR steelhead.
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