Dynamics of Consumption and Food Conversion by Lake Michigan Alewives: An Energetics-Modeling Synthesis

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Abstract
We developed an energetics model for the alewife Alosa pseudoharengus to evaluate consumption and conversion efficiency processes. We estimated alewife standard metabolism (R) as a function of wet body weight (W, g) and water temperature (T, °C): R (g˙g−1˙d−1) = 0.0073 W−0.215e0.0548T. We estimated maximum daily ration for 15‐g, yearling alewives at 20°C to be as much as 37% of their body weight in experiments of 24 h. Modeling simulations based on observed growth in Lake Michigan indicated that yearling alewives may attain close to 70% of their estimated maximum consumption rate during September and October. Simulation results indicated wide seasonal variations in consumption rates; almost 50% of the yearly consumption by an individual adult alewife (age ≥ II) occurs in September and October, suggesting abundant food and possibly relaxed competition during that season. In contrast, adult alewives lose weight during the summer when stratification of Lake Michigan would permit orientation to water temperatures optimal for growth, suggesting that serious food limitations during that period may heighten competitive interactions. Over an annual cycle, adults converted only 1.3–2.8% of food consumed (wet weight) to body biomass; young of the year converted 5%. Conversion of energy consumed to body energy was higher than biomass conversion, but still relatively low for older age‐classes–2.3–5.2% for adults and 12.7% for young of the year. Total annual consumption and conversion efficiency estimates were relatively insensitive to assumptions about seasonal dynamics of body energy density (J˙g−1 wet weight) but within seasons when energy density was changing rapidly, an assumption of constant energy density yielded errors of −45% to 104% for those variables.

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