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 hydrosystem mortality, water diversions, excessive sediment, and
degraded water quality. Elevated temperature also impacts the status of SR steelhead. Pesticides
have been detected in SR steelhead freshwater habitats. NAWQA sampling in 1992-1995 in the
DPS’s watersheds detected Eptam, atrazine, desethylatrazine, metolachlor, and alachlor.
Carbaryl and carbofuran were detected in only 1% of samples. The combined impacts from
these multiple threats continue to affect SR steelhead.
Some spawning and rearing habitat of the Snake River steelhead is in forested areas, where
carbaryl may be applied. However, the likelihood of exposure in forested areas is unknown.
Registered 24(c) uses within this ESU include carbofuran application to potatoes and spinach
grown for seed in Washington. Dryland agriculture occurs in lower Clearwater Basin, with crops
including wheat, peas, and lentils. Alfalfa, hay, and grasses are also grown in the lower
Clearwater as well as the lower Salmon River basin. All three a.i.s are registered for use on
alfalfa. Agricultural activities and urban communities are concentrated along the Snake River
and near the mouths of major tributary valleys, thus stream water quality and biological
communities in the downstream portion of the upper Snake River basin are degraded. Given that
urban and agricultural areas are located adjacent to streams in the Lower Clearwater River
drainage, DPS exposure to these pesticides is likely.
Sexually immature adult Snake River summer steelheads enter the Columbia River from late
June to October. Adults migrate upriver until they reach Snake River tributaries where they
spawn between March and May of the following year. Emergence occurs by early June in low
elevation streams and as late mid-July at higher elevations. After hatching, juvenile SR
steelhead typically select off-channel habitats associated with their natal rivers and streams for
rearing. They spend two to three years in freshwater before they smolt and migrate to the ocean.
Juvenile steelhead are more likely to be exposed to pesticides and other contaminants because of
their long freshwater residency period.
Given the life history of SR steelhead, we expect the proposed uses of carbaryl and carbofuran
pesticide products that contaminate aquatic habitats will lead to individual fitness level
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