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

Additionally, the macroinvertebrate communities in these systems were compromised to such an
extent that there was a reduction in salmonid prey abundance. These findings highlight the
importance of characterizing the presence of AChE insecticides, N-methyl carbamates and OPs,
within aquatic habitats because the compounds share a mode of action and adverse biological
responses to mixtures containing multiple AChE insecticides are likely cumulative. These data
can serve as a surrogate for expected effects of the aquatic community when concentrations of
carbaryl, carbofuran, and methomyl attain effect thresholds.
Field studies in ESA-listed salmonid habitats: Willapa Bay and Grays Harbor Washington
History of Carbaryl use in Washington estuaries
Willapa Bay and Grays Harbor support large commercial oyster-producing areas (approximately
600 acres in Willapa and 200 acres in Grays Harbor) and are located north of the Columbia River
along the southwestern coast of Washington. The Pacific oyster (Crassostrea gigas), introduced
from Japan in the 1920s, is the principal species cultivated in those estuaries (Feldman,
Armstrong et al. 2000). Two species of endemic shrimp, ghost shrimp (Neotrypaea
californiensis) and mud shrimp (Upogebia pugettensis), are abundant in the oyster growing areas
of these estuaries and create burrows in the sediment that are unfavorable for optimal oyster
cultivation. The Washington State oyster industry has used aerial applications of carbaryl to kill
the burrowing shrimp in oyster beds since the early 1960s. EPA authorizes the use of carbaryl
on oyster beds in Washington through a SLN label, or Section 24(c) (EPA Reg. No. 264-316).
Carbaryl is applied directly to intertidal areas when they are exposed at low tide, primarily by
helicopter (Dumbauld, Brooks et al. 2001). This use has been controversial and there have been
numerous studies dating back several decades that evaluated the ecological impact of carbaryl
use in these two estuaries (Feldman, Armstrong et al. 2000). Although the EPA label does not
limit applications to Willapa Bay and Grays Harbor, historically these have been the only areas
treated with carbaryl. Additionally, Washington State requires applicators to obtain NPDES
permits for applications to aquatic habitats.
ESA-Listed Pacific salmonids that occur in Willapa Bay and Grays Harbor
Juvenile and adult Chinook salmon from ESA-listed populations are expected to be present in
Willapa Bay and Grays Harbor at the time of carbaryl applications. It is expected that juvenile
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