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

Effects to salmonid populations from reduced size of juveniles due to impaired feeding and
reduced abundance of aquatic prey
To evaluate the potential for adverse effects to juvenile growth resulting from carbaryl,
carbofuran, and methomyl on Pacific salmonid populations, we developed a model (Appendix
1). The model links AChE inhibition, feeding behavior, prey availability, and somatic growth of
individual salmon to the productivity of salmon populations expressed as a percent change in
lambda (a population’s intrinsic rate of growth). The model scenarios (single insecticide or
multiple pulses of single insecticides) assume annual exposure of all the subyearling juveniles in
the population and their prey to the insecticide. Similar to the survival model, we developed the
growth model for four populations of salmonids: ocean-type Chinook, stream-type Chinook,
sockeye, and coho salmon.
We integrated two avenues of effect to juvenile salmonids’ growth from exposure to the three Nmethyl
carbamates (Appendix 1). The first avenue is a result of AChE inhibition on the feeding
success and subsequent effects to growth of juvenile salmonids. Study results with juvenile
salmonids show that feeding success is reduced following exposures to AChE inhibitors
(Sandahl, Baldwin et al. 2005). The second avenue the model addresses is the potential for
reductions in juvenile growth due to reduction in available prey. Salmon are often found to be
food limited in freshwater aquatic habitats, suggesting that a reduction in prey due to insecticide
exposure may further stress salmon and lead to reduced growth rates. Field mesocosm data
support this assertion, showing reduced growth of juvenile fish following exposure to the AChE
inhibitor, chlorpyrifos (Brazner and Kline 1990). Furthermore, based on our review of the
sensitivities of aquatic invertebrates to the three insecticides, we expect reductions in densities
and altered composition of the salmonid prey communities.
Reductions in aquatic prey are included in the model because of the high relative toxicity of
pesticides to salmonid prey and the extended duration of effects on prey communities. Juvenile
salmonids are largely opportunistic, feeding on a diverse community of aquatic and terrestrial
invertebrate taxa that are entrained in the water column or on the surface (Higgs, Macdonald et
al. 1995). As a group, these invertebrates are among the more sensitive taxa for which there is
toxicity data, but within this group, there is a wide range of sensitivities (Table 64, Table 65).
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