Predicting ingestion times of individual prey from information about stomach contents of predatory fishes in the field

Abstract

In contrast to previous approaches, and incorporating interactions between individual prey in the stomach, the cylinder model of gastric evacuation predicted accurately the ingestion times of individual prey recovered from stomachs of predatory gadoids sampled in laboratory experiments. For application to field situations, estimates of the variance σ τ 2 = ( σ τ , e 2 + σ τ , m 2 ) of the predicted time interval τ between prey ingestion and stomach sampling were obtained from generalised considerations about the errors of estimated gastric evacuation rate ( σ τ,e ≅ 0.10 τ) and prey size at ingestion ( σ τ, m increased from 1 h to 2.5 h with increasing number and body size of other prey in the stomach). The bias originating from non-observable prey (that were completely evacuated from the stomach prior to sampling) may amount to more than 20% and should be taken into consideration. In contrast, the sensitivity of τ to estimated body lengths of other prey recovered as small remains from the stomach was generally low. These error and bias considerations render possible an appraisal in advance of the precision and the accuracy and, so, of the usefulness of the method in specific field studies on the feeding biology of predatory fishes.