Precision of ingestion time and evacuation predictors for individual prey in stomachs of predatory fishes

Without evaluating precision, gastric evacuation models in combination with stomach data are widely used to investigate the feeding biology of wild predatory fishes. Assuming each predator individual to operate with its own evacuation rate parameter, the precision of estimated ingestion times for individual prey in the stomachs of predatory fishes was derived in this study. This way, the variability of gastric evacuation not accounted for by a deterministic model of gastric evacuation was described. The variability of initial body mass of ingested prey was included as well. General values 0.03 and 0.10 of the coefficients of variation σm and σe were obtained for the square root of initial prey mass and the evacuation rate parameter, respectively. They were estimated from length–mass data on a variety of fresh prey fishes and from data on gastric evacuation in the predatory gadoids whiting (Merlangius merlangus), Atlantic cod (Gadus morhua), and saithe (pollock) (Pollachius virens). Deriving the variance of gastric evacuation rate, evacuation time, and remaining prey mass, the study also established a basis for statistical analyses of the results obtained from laboratory experiments on gastric evacuation.