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

Central California Coast Coho Salmon
The CCC coho salmon ESU includes 11 historical independent populations within counties from
Mendocino to Santa Cruz in California. Coho populations in three larger watersheds, as well as
some in smaller watersheds, have been extirpated or are nearly so. Historical escapement has
been estimated between 200,000 and 500,000 fish. Current escapements are not known, though
a minimum of 6,570 adult coho salmon are estimated to return to coastal streams within the ESU.
Long-term population trends do not exist for any of the populations in this ESU. More fish enter
northern streams but variation in abundance between cohorts can be large with one cohort often
dominating. Southern streams produce few naturally spawned fish of all cohorts.
CCC coho salmon populations have been adversely affected by loss of riparian cover, elevated
water temperatures, alteration of channel morphology, loss of winter habitat, and siltation. High
water temperatures prevent coho salmon from inhabiting several streams within the ESU.
Pesticides are expected to enter rivers as drift during application in agricultural areas. Highly
contaminated runoff into the Russian River, San Francisco Bay, and into rivers south of the
Golden Gate Bridge is expected during the first fall storms. We expect that application of other
AChE inhibiting pesticides will co-occur with carbaryl, carbofuran, and methomyl in the waters
within the ESU and exacerbate adverse effects from AChE inhibition.
The majority of agricultural land use is concentrated in the Russian River watershed and
watersheds south of the Golden Gate Bridge. High density urban development and urban centers
occur in the San Francisco Bay and in the Russian River basin. All three a.i.s are expected to be
applied to several crops within the Russian River basin and the Santa Cruz stratum during the
growing season. Carbaryl is expected to be used within urban/residential areas throughout the
entire year.
The movements of mature adults are influenced by stream flow; entry often occurs during the
first large winter storms. Similarly, CCC coho salmon adults must wait in the lower river for
sufficient flow to be able to reach spawning grounds. Fry emerge in spring and remain in the
stream for up to 18 months. Newly emerged fry use backwater, side channels, and shallow
channel edges. During winter, juveniles inhabit side channels, sloughs, backwater, and other
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