THE ROLE OF EXPERIENCE IN RISK ASSESSMENT - AVOIDANCE OF AREAS CHEMICALLY LABELED WITH FATHEAD MINNOW ALARM PHEROMONE BY CONSPECIFICS AND HETEROSPECIFICS

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 fat head minnow alarm pheromone. There was an initial decrease in the numb er of fish caught in areas labelled with alarm pheromone (risky areas) relative to areas labelled with distilled water (safe areas), after t he source of the pheromone was removed. Numbers of minnows or stickleb ack caught in risky and safe areas were no longer different 4 hours af ter the pheromone source was removed. For minnows, there was no signif icant difference in the immigration rates of individuals into risky an d safe areas from neighbouring locations. For minnows, and probably st ickleback new individuals, naive to the association of an area with al arm pheromone, immigrated into risky areas before the return of experi enced fish. Fish present at the time of pheromone release did not retu rn for 7 or 8 hours after the source of the pheromone was gone. This r aises the possibility that the chief beneficiaries of chemical alarm s ignals may be only those individuals present at the time of pheromone release.