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

Transect surveys conducted on treatment beds the day following applications indicate large
numbers of crabs are killed by the applications (Table 69). Other acute mortalities to non-target
organisms were generally not reported. However, transect surveys were conducted during 1986
and 1987 due to concerns over potential impacts to fish given staff observations from the
Washington Department of Fisheries reported that fish mortality was “routinely” noted, but not
quantitatively assessed following applications of carbaryl (Tufts 1989). Mortalities were
characterized as small fish apparently trapped in shallow pools during low tide and directly
exposed during carbaryl treatments. The surveys indicate several thousand fish were killed each
year from carbaryl applications to approximately 400 acres at rates of ≤ 7.5 lbs a.i./acre (Table
70). Currently, the NPDES permit allow for treatment of up to 600 acres. The current 24 (c)
label does not specify acreage restrictions and allows for applications of carbaryl up to 8 lbs
a.i./acre.
Table 69. Estimated dungeness crab mortalities resulting from carbaryl applications in Willapa
Bay and Grays Harbor, Washington
Year Maximum Application Rates* Total Acres Treated** Dungeness Crab Killed
1984 ≤ 10 lbs a.i. / acre 490 38,410
1985 ≤ 7.5 lbs a.i./acre 391 59,933
1986 ≤ 7.5 lbs a.i./acre 398 16,286
1987 ≤ 7.5 lbs a.i./acre 434 44,053
* Current 24(c) label allows for application of up to 8 lbs a.i./acre
** Current NPDES permit allows for a total of 600 hundred acres to be treated in Willapa Bay and Grays
Harbor, WA. The Label places no restrictions on acres or geographic restrictions for use of carbaryl on
oyster beds in Washington.
Given that the fish that reside in standing water on mud flats are likely to be the most vulnerable
to carbaryl exposure, staff from the Washington Department of Fisheries also estimated the
available marine fish habitat that existed on exposed mudflats of treated areas. They
characterized water that was at least 2 inches in depth, a depth that is adequate for salmon fry, as
marine habitat. This habitat comprised substantial portions of the treated areas. In 1986, surveys
indicate 135 acres of the 398 of the treated area (approximately 34%) were marine fish habitat
(Tufts 1989). In 1987, 67 of the 434 (15%) acres were characterized by Washington Department
of Fisheries as marine fish habitat. The current NPDES permit specifies that there be a 200 ft
buffer zone for sloughs and channels when carbaryl is applied by helicopter. A 50 ft buffer is
required for those aquatic habitats when carbaryl is applied by hand sprayer. AgDrift estimates
for aerial application at an application rate of 8 lbs a.i./acre with a 200 ft buffer indicate the
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