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r <br />endangered species, since large numbers of prey are required for the experiments. Also, <br />estimated predation rates are very likely higher than true rates because enclosures are generally <br />too small to allow prey species to employ natural antipredation strategies (see review by Dodson <br />et al. 1994). <br />Bioenergetics modeling is a relatively new method that could become increasingly useful in <br />estimating predation potential on endangered fish species. Because this method involves <br />calculating amass-balance energetic budget using energy expenditure and growth of the predator <br />and the proportional weight and energy contribution of each prey type, predation potentials can <br />be estimated without sacrificing or handling large numbers of prey items (Ney 1993). Winberg <br />(1956) was the first to use a bioenergetics approach for fish. This methodology has since been <br />elaborated upon by numerous authors, most notably (Hewett and Johnson 1987, 1992). Hewett <br />and Johnson developed amicrocomputer-based energetics model that is widely used in North <br />America (Brandt and Hartman 1993). These models partition energy consumption into growth, <br />metabolic costs, and waste. The balanced energy equation can be solved for any one of the <br />terms if the other three are known. <br />While bioenergetics approaches have mostly been used to estimate the amount of forage needed <br />to sustain a desired fishery, we suggest that this approach is valuable for estimating or <br />quantifying predation losses on target prey species (also see Post and Rudstam 1992; Hansen et <br />al. 1993; Beauchamp et al. 1995), especially when absolute minimal handling of prey species <br />(e.g. endangered species) is required. In this paper, we employ a bioenergetics approach to <br />estimate the potential effect of predation by the introduced northern pike (Esox Lucius) on the <br />