The role of experience in risk assessment: Avoidance of areas chemically labelled with fathead minnow alarm pheromone by conspecifics and heterospecifics

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Abstract
In two field experiments, we investigated risk avoidance behaviour by individual fathead minnows (Pimephales promelas Rafinesque) and brook stickleback (Culaea inconstans Kirtland) in response to release of fathead minnow alarm pheromone. There was an initial decrease in the number of fish caught in areas labelled with alarm pheromone (risky areas) relative to areas labelled with distilled water (safe areas), after the source of the pheromone was removed. Numbers of minnows or stickleback caught in risky and safe areas were no longer different 4 hours after the pheromone source was removed. For minnows, there was no significant difference in the immigration rates of individuals into risky and safe areas from neighbouring locations. For minnows, and probably stickleback, new individuals, naive to the association of an area with alarm pheromone, immigrated into risky areas before the return of experienced fish. Fish present at the time of pheromone release did not return for 7 or 8 hours after the source of the pheromone was gone. This raises the possibility that the chief beneficiaries of chemical alarm signals may be only those individuals present at the time of pheromone release.