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

The major threats to this DPS identified in the Status of Listed Resources and Environmental
Baseline sections are timber harvest, forest roads, vineyard developments, and road crossings
and dams. Stressors to the NC steelhead include lack of large instream woody debris, reduced
riparian vegetation, elevated water temperature, increased predation, and barriers that limit
access to tributaries. The combined impacts from these multiple threats continue to affect the
NC steelhead.
About 85% of the land use for this DPS consists of forests and chaparral (Table 26). Atlhough
carbaryl may be applied in forested areas, the extent of exposure is unknown. There are areas of
Mendocino County with a high density of vineyards, and there is some crop farming in low
laying areas and floodplains along the estuaries and lower reaches of coastal streams. Coastal
communities are located at the mouths of several streams within the NC steelhead DPS. Based
on the crop types, we expect carbaryl, carbofuran, and methomyl to be commonly applied
throughout the growing season in these areas. Carbaryl is expected to be used the entire year
within urban and residential areas. However, because agricultural and urban development is not
concentrated in any one basin, the risk of exposure to any given population is decreased.
Additionally, the majority of steelhead juveniles rear at higher elevations in the watersheds with
less agricultural influence. The fry, then, are less likely to be exposed during critical life stages.
The winter-type steelhead enters rivers as mature adults between November and April to spawn.
The summer-type enters the stream in immature condition between May and October. Early
arriving summer steelehead move high into the upper watersheds where they hold in deep pools
throughout the summer before spawning in fall. In northern California, juvenile steelhead
remain in freshwater for two or more years before migrating downstream to smolt. Juvenile
steelheads spend a variable amount of time in the estuary before entering the open ocean.
We expect the proposed uses of carbaryl, carbofuran, and methomyl pesticides products within
this DPS may lead to individual fitness effects, ranging from acute lethality to temporary AChE
inhibition. However, exposure of NC steelhead populations to the three carbamates will be
limited given the amount of overlap between agriculture, residential and urban development and
spawning and rearing habitat. As such, we do not expect exposure to result in population-level
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