Feeding ecology of age-0 lake whitefish in Saginaw Bay, Lake Huron

Age-0 lake whitefish Coregonus clupeaformis (11-160. mm total length) were collected from Saginaw Bay, Lake Huron during April-November 2009 and 2010 for diet analysis and for the evaluation of ontogenetic changes in feeding ecology. Lake whitefish ≤ 50. mm ate mainly zooplankton, after which their diets switched mainly to benthic macroinvertebrates. Cyclopoida were the dominant prey consumed by very small lake whitefish (< 17. mm) and the most frequently selected zooplankton type for individual small fish. Once lake whitefish reached 18-19. mm, Cyclopoida in the diet declined and cladocerans emerged as an important diet item. Daphnia were the most common cladoceran in the diets, but for fish 31-50. mm Bosminidae were also relatively important. Although the shift to Daphnia could represent an ontogenetic point when lake whitefish were large enough to effectively handle this prey, it also took place when the relative availability of Daphnia increased. Once lake whitefish were > 50. mm, Chironomidae larvae became a dominant prey item and this shift to benthivory coincided with a 55% increase in length-adjusted energy content between June and July. However, as fish grew (around 110-120. mm), Sphaeriidae and the benthic zooplankton Chydoridae became increasingly important in the diet. As these less energetically rich prey were incorporated into the diet, there were corresponding 21 and 15% decreases in length-adjusted energy content from July to August and September, respectively.