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

The major threats to this DPS identified in the Status of Listed Resources and Environmental
Baseline sections include dams that block fish migration and alter river hydrology; water
diversions; destruction or degradation of riparian habitat; and land use practices (logging,
agriculture, urbanization). Elevated water temperature and poor water quality also affect the
status of UCR steelhead. Pesticides have also been detected in UCR steelhead freshwater
habitats. NAWQA sampling from 1992-1995 in the Central Columbia Plateau detected
numerous pesticides in surface water (Williamson et al. 1998). Carbaryl was detected in 5% of
samples, and carbofuran was detected in 6%. Methomyl was not detected. While detections of
these three chemicals did not exceed water quality standards, concentrations of six other
pesticides exceeded EPA criteria for the protection of aquatic life. The co-occurrence of atrazine
with carbaryl and other OPs in aquatic habitats increases the likelihood of adverse responses in
salmonids and their aquatic prey. The combined impacts from these multiple threats continue to
affect UCR steelhead.
Land uses within this DPS range include agricultural, urban and residential development. Based
on the crop types, we expect that carbaryl and methomyl are commonly applied in the
Wenatchee, Methow, and Entiat subbasins throughout the growing season. Existing stocks of
carbofuran are also expected to be applied throughout the growing season. As runoff containing
pesticides and other contaminants from the above land uses drain into the Wenatchee, Entiat, and
Methow Rivers, DPS exposure to these pesticides is likely. We also expect other AChE
inhibiting pesticides will co-occur with carbaryl, carbofuran, and methomyl in the waters of the
Wenatchee, Entiat, Methow, and Lower Crab Creek subbasins and exacerbate adverse effects
from AChE inhibition.
UCR adults return to the Columbia River in the late summer and early fall. UCR steelhead
spawn and rear in the major tributaries to the Columbia River between Rock Island and Chief
Joseph dams. Adults reach spawning areas in late spring of the calendar year following entry
into the river. Newly emerged fry move about considerably and seek suitable rearing habitat,
such as stream margins or cascades. Steelhead fry typically select off-channel habitats
associated with their natal rivers and stream for extended periods of rearing. Fry move
downstream in the fall in search of suitable overwintering habitat (Chapman, Hillman et al.
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