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

Because olfaction plays an important role in a suite of ecologically relevant behaviors that are
affected when an individual salmonid’s olfaction is impaired, we include this endpoint in our
analysis. Lack of predator avoidance behaviors by juvenile and adult salmonids reduces the
probability of surviving predation events. Juvenile salmonids with impaired olfaction may fail to
properly imprint on their natal waters, which later in life leads to adults straying i.e., migrating
into and spawning in streams other than their natal stream. Adults that do not return to natal
waters are a functional loss to recruitment of a population. Adult male salmonids that do find
their way back to natal stream or river reaches and are subsequently exposed to the three
insecticides may lose some or all of their olfactory capacity, even from a short-term exposure.
Female salmonids release odorants to trigger male priming hormones and to alert males of a
female’s spawning condition. However, male fish with reduced olfactory capacity may not
detect these cues, as demonstrated in a study on carbofuran (Bretaud, Saglio et al. 2002). Thus
spawning synchronization could be compromised and recently laid eggs may go unfertilized.
Unfertilized eggs may result in reduced productivity and abundance for a population if sufficient
numbers of spawning events are missed. Again, we find it difficult to accurately predict when
these impairments and missed spawning opportunities occur, primarily as a result of incomplete
pesticide use information, difficulty in conducting field experiments with adult salmonids, and
uncertainties surrounding extent of effects and concentrations which may trigger them. Because
imprinting, avoiding predators, homing, and spawning are likely affected when exposed to
carbofuran, we conclude these additional effects cannot be dismissed. Therefore, we expect
populations exposed to carbofuran will show reduced reproductive rates, reduced return rates,
and reduced intrinsic rates of growth when sufficient numbers of individuals are affected.
Starvation during a critical life stage transition
Salmonids emerge from redds (nests) with a yolk-sac as their initial food source (yolk-sac fry).
Once the yolk-sac has been completely absorbed, they must begin exogenous feeding. Fry have
limited energy reserves, and if they are unable to properly swim or detect and capture prey the
onset of starvation occurs rapidly. Because juvenile salmon are limited by gape width, prey at
this stage are limited to very small aquatic invertebrates. The stressors of the action likely affect
this critical life stage transition in several ways, leading to increased early life stage mortality.
Impaired swimming and olfaction affects the fry’s ability to detect and capture prey. Prey may
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