Use of diagnostic bones to identify and estimate original lengths of ingested prey fishes

We examined and measured cleithra, dentaries, opercles, and pharyngeal arches – bones found to persist during digestion of most prey fish – to identify 24 prey fish species and back-calculate their original fork length. Eighteen of the 24 species examined could be easily distinguished; however, for certain congenerics, identification was neither consistent nor reliable for all bones within the size ranges examined. Relations between bone length and fish length were linear for 14 species for which the sample sizes were adequate (N > 30); coefficients of determination (r ²) ranged from 0.79 to 0.99. Diagnostic characteristics and measurements of these bones provided reliable identification of genera and species and estimates of original fork lengths of partly digested prey fish from three predators. This method, compared with that of examining only prey fish in a measurable condition, greatly increased the amount of dietary information available from gut analysis.