Laboratory studies on foraging patterns of age-0 lake whitefish and cisco provide insights into recent recruitment patterns in Lake Michigan

Abstract

Populations of lake whitefish ( Coregonus clupeaformis ) and cisco ( C. artedi ) in Lake Michigan are currently much less abundant than reported in historical records. Currently, cisco populations are increasing in northern Lake Michigan, while lake whitefish are declining. Unidentified early life stage bottlenecks are likely driving the differing recruitment patterns. We examined the foraging abilities of larval, early juvenile, and later juvenile lake whitefish and cisco in laboratory experiments which determined capture rate ( a ), handling time ( h ), and theoretical maximum consumption ( Nmax ) and developed type-II functional response models. Mouth gape was measured to inform foraging patterns of the two species across early life stages. Prey selectivity was evaluated for larvae and early juveniles of each species when consuming a mix of prey at satiation densities. Larval cisco were more successful in capturing and handling Artemia nauplii than lake whitefish. Early and later stage juvenile lake whitefish captured more Bosmina and chironomid larvae than cisco. Later juvenile cisco more successfully captured and handled cyclopoid copepods than lake whitefish. Early juvenile lake whitefish selected positively for cladoceran taxa and avoided copepods, while cisco fed non-selectively on the most abundant taxa. Lake whitefish had a larger mouth gape than cisco until the later juvenile stage, when the gape size of cisco surpassed that of lake whitefish, and likely enhanced their ability to forage on larger prey (i.e., copepods). Present-day conditions in northern Lake Michigan, where abundance of cladocerans is low, chironomid larvae are variable, and copepods dominate, may provide an advantage to cisco over lake whitefish.