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direct estimates of predation rates, but is not acceptable for examining predator/prey interactions ' involving endangered species, since large numbers of prey are required for the experiments. Also, estimated predation rates are very likely higher than true rates because enclosures are generally small enou h to restrict natural anti redation strate ies em to ed by rey species (see review by g P g P Y P ' Dodson et al. 1994). An additional method that could become increasingly useful in estimating predation potential on ' endangered fish species involves the use of bioenergetics modeling. Because this method ' involves calculating amass-balance energetic budget using energy expenditure data for the -- predator and only energy content of the prey, predation potentials can be estimated without ' sacrificing or even handling large numbers of prey items (Ney 1993). Winberg (1956) was the ' first to use a bioenergetics approach for fish. This methodology has since been elaborated upon by numerous authors, most notably (Hewett and Johnson 1987, 1992). Hewett and Johnson have provided a microcomputer version of an energetics model that is now the most widely used ' version in North America (Ney 1993). Simplistically, these models partition consumed food into growth, metabolic costs and waste. If any three of the above parameters are known, the fourth ' can be Basil estimated. Y While bioenergetics approaches are mostly used to estimate the amount of forage needed to sustain a desired fishery, we suggest that this approach is a valuable way to estimate the ' consumption of different predators on target prey species (also see Post and Rudstam 1992, ' Brandt et al. 1992), especially when absolute minimal handling of prey species (e.g., endangered ' 2