| I used stable isotope analysis to estimate walleye trophic position and then compared these values to trophic position estimates from diet content analysis for fish sampled from May 2001 to May 2002. Trophic position estimates generated by isotopes were not correlated to those estimated from diet composition. However, because isotope signatures reflect an integrated feeding history, when corrected for seasonal time lags, isotope signatures strongly corresponded to cumulative diet composition. Furthermore, walleye isotope signatures quantified both annual changes in prey use and spatial differences across reservoir zones (riverine, transition, and lacustrine). Spatial differences in prey consumption strongly corresponded to spatial differences in isotope estimates. Using biplots of trophic position versus delta13C, I show how seasonal and spatial variation in energy flow can be used for monitoring changes in prey use. (Abstract shortened by UMI.)... |
