Comparison between consumption rates of yellow perch (Perca flavescens) estimated with a digestive tract model and with a radioisotope approach
We compared consumption rates of yellow perch (Perca flavescens) obtained from surveys of complete digestive tract contents (CDTC) with two radioisotope approaches using 137Cs as a biological tracer. We sampled fish of age 1+, 2+, and 3+ from three lakes for a total of six lake - age-class combinations. The two radioisotope methods provided very similar estimates of consumption rates. The relative differences between the CDTC approach and the radioisotope approaches ranged from 67 to 128% when the sampling interval length was 28-35 days. At the time scale of 70 days, the relative differences between the approaches ranged from 15 to 20%. We propose that the ratio of the sampling interval length to the biological half-life of the contaminant determines the discrepancy between consumption estimates obtained using CDTC and radioisotopic approaches. Our analyses suggest that, under the specific conditions encountered in our study, a minimum value for this ratio to obtain adequate consumption rates may be 45%. Although our work represents a corroboration of the radioisotope approach in systems where 137Cs is present at trace levels, it also suggests that consumption rates obtained for time periods shorter than 70 days should be interpreted with caution.