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

single pulse of chlorpyrifos was introduced into each enclosure at day 0. Invertebrate abundance
was determined in each replicate on days -3, 4, 16, and 32. Fathead minnows were sampled
from enclosures on days -2, 7, 15, and 31 where fish were weighed, measured, and dissected to
determine gut content (dietary items identified). By day 7, significant differences in mean
numbers of rotifers, cladocerans, protozoans, chironomids, mean total number of prey being
eaten per fish, and mean species richness were greater in fish from the control enclosures than in
some of the treatments. By day 15, control minnows were significantly larger than fish from
treated levels. These experimental results support the conclusion that reductions in abundance of
prey to juvenile fish can result in significant growth effects. It is reasonable to assume that
reductions in prey from carbamate insecticides can also result in reduced juvenile salmonid
growth and ultimately reduced survival and productivity. The precise levels of prey reduction
necessary to cause subsequent reductions in salmonid growth remain a recognized data gap.
Recent declines in aquatic species in the Sacramento-San Joaquin River Delta in California have
been attributed in part to toxic pollutants, including pesticides (Werner, Deanovic et al. 2000).
Significant mortality or reproductive toxicity in C. dubia was detected in water samples collected
at 24 sites in the Sacramento-San Joaquin River Delta in California. Ecologically important back
sloughs had the largest percentage of toxic samples (14 - 19%). The TIEs identified carbofuran
and carbaryl as well as the OPs chlorpyrifos, diazinon, and malathion as the primary toxicants in
these samples responsible for the adverse effects (Werner, Deanovic et al. 2000).
Recovery of salmonid prey communities following acute and chronic exposures from carbaryl,
carbofuran, and methomyl depends on the organism’s sensitivity, life stage, length of life cycle,
among other characteristics. Univoltine species will take longer than multivoltine species to
recover (Liess and Schulz 1999). Recovery of salmonid prey items such as caddisflies,
stoneflies, and mayflies will be slow, considering their long life cycles and infrequent
reproduction. Additionally, these species also require clean, cool waters to both recover and
maintain self-sustaining populations. In several salmonid-supporting systems these habitats are
continually exposed to anthropogenic disturbances, including pesticide contamination, which
limits their recovery and can also limit recovery of multivoltine species. For example, urban
environments are seasonally affected by stormwater runoff that introduces toxic levels of
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