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

In a second modeling exercise, we translate reductions in growth of juvenile salmon from AChE
inhibition and from reduced prey abundances to potential population impacts using individualbased
growth and life history population models (Appendix 1). These two endpoints (AChE
inhibition and reduced prey abundance) are combined in the model to evaluate population-level
effects due to reductions in first year survival of juveniles (Appendix 1). Similar to the survival
models, percent change in lambda is the output. We discuss the significance of population
changes in the context of departures from normal variability of the unexposed population and
expected environmental concentrations. We conclude this section on population-level effects
with a discussion of population-level responses to other affected salmonid endpoints that were
not modeled. These include effects from other stressors of the proposed action, mixture effects,
and effects to behaviors from impaired olfaction and AChE inhibition such as swimming
behaviors.
Salmonid Population Models
We selected four generalized life history strategies to model (Appendix 1). We ran general life
history matrix models for coho salmon (Oncorhynchus kisutch), sockeye salmon (O. nerka) and
ocean-type and stream-type Chinook salmon (O. tshawytscha). We did not construct a steelhead
(O. mykiss) life history model due to the lack of demographic information. Chum salmon (O.
keta) were omitted from the growth model exercise because they migrate to marine systems soon
after emerging from the gravel and the model assesses early life stage growth effects over a
minimum of 140 d in freshwater systems. The basic salmonid life history we modeled consisted
of hatching and rearing in freshwater, smoltification in estuaries, migration to the ocean,
maturation at sea, and returning to the natal freshwater stream for spawning followed shortly by
death. For specific information on how we constructed the models see Appendix 1.
Effects to salmonid populations from death of sub­yearling juveniles
An acute toxicity model was constructed that estimated the population-level impacts of
subyearling juvenile (referred to as juveniles within this section) mortality resulting from
exposure to concentrations of carbaryl, carbofuran, and methomyl. These models excluded
sublethal and indirect effects of the pesticide exposures and focused on the population-level
outcomes resulting from an annual 4 d exposure of all juveniles in the population to carbaryl,
carbofuran, and methomyl from single exposures. Death of juveniles was implemented as a
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