Since 1980, there have been perhaps 30 significant studies of chaetognath gut
contents along the same lines. Baier and Purcell (1997) tested the importance of
immediate defecation (or vomiting) of recently eaten prey on capture for Sagitta
(Flaccisagitta) enflata, which eliminates meals that should have been counted. They
compared 2-minute hauls (immediately preserved) to 5-minute and longer hauls,
finding a drop from more than half of worms having gut content to only a quarter.
This would shift gut-content results dramatically in respect to both chaetognath
nutrition and the quantification of their impact on prey stocks. That conclusion can be
generalized: gut-content studies are of great qualitative value and are consistently
problematic for quantitative purposes. While calculations can be made of organic-
matter intake rates (for chaetognaths see Pearre 1981) by multiplying (meals per
predator) × (meal mass) × (a gut-residence time of meals from experiments, often a
function of temperature), such estimates suffer from multiple biases. On the other
hand, gut contents do identify what animals eat, the times of day that eating occurs,
and approximately the degree to which prey are eaten as encountered or are chosen
selectively.
(^) There are studies like those for chaetognaths for a wide range of animals, especially