A change in the pattern of vertical migration of Chaoborus flavicans after the introduction oftrout

The pattern of diel vertical migration exhibited by Chaoborus flavicans in Lake Lenore, Washington has changed over the past decade. Formerly Chaoborus larvae and pupae were present in the water column during the day. Since 1982, a strong pattern of diel vertical migration has been evident in this population. Third and fourth instar larvae and pupae reside in the sediments during the day and then ascend to the surface waters at night. The change in migratory activity of C. flavicans was coincident with the introduction of cutthroat trout ( Salmo clarki henshawi ) into Lake Lenore in 1979. Predation by trout on fourth instar larvae and pupae of C. flavicans was probably responsible for the observed changes in migratory behavior