Ecological divergence between emerald and spottail shiners (Notropis) in Lake Manitoba

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Bernard, Donald Jean
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In Lake Manitoba two cyprinid species (Notropis) occur sympatrically and show ecological divergence. In July and August the fry of emerald shiners were near the surface in the limnetic zone while spottail shiners appeared to be littoral. By September both species were most abundant near shore and, overlapped in vertical distribution. Emerald shiner fry fed on plankton, and spottail shiner fry on plankton and bottom foods. Emerald shiners of age I and older in May and June were mainly in offshore surface waters and at shoal edges occupying the whole water column. Spottail shiners of age I and older were near the bottom onshore in the shoal waters. As the season progressed, spottail shiners appeared to move offshore and off the bottom, while emerald shiners moved on to shoal waters but were most abundant near the surface or midwater. Emerald shiners showed a diel onshore-offshore movement, which occurred at irregular times in June, July and August, and a diel vertical movement to the surface at night in June and July. Spottail shiners showed, no diel movements but appeared to be inactive between dusk and dawn. The diet of both species reflected their spatial distribution. Emerald shiners fed primarily on plankton, and spottail shiners ate mainly bottom food but both shared a common diet of Diptera larva in July. The ecological segregation between the two cohabiting congeneric species is possibly due to selective segregation.