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Bias in estimating food consumption of fish by stomach-content analysis

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Abstract:

This study presents an analysis of the bias introduced by using simplified methods to calculate food intake of fish from stomach contents. Three sources of bias were considered: (1) the effect of estimating consumption based on a limited number of stomach samples, (2) the effect of using average contents derived from pooled stomach samples rather than individual stomachs, and (3) the effect of ignoring biological factors that affect the evacuation of prey. Estimating consumption from only two stomach samples yielded results close to the actual intake rate in a simulation study. In contrast to this, a serious positive bias was introduced by estimating food intake from the contents of pooled stomach samples. An expression is given that can be used to correct analytically for this bias. A new method, which takes into account the distribution and evacuation of individual prey types as well as the effect of other food in the stomach on evacuation, is suggested for estimating the intake of separate prey types. Simplifying the estimation by ignoring these factors biased estimates of consumption of individual prey types by up to 150% in a data example.

Nous présentons une analyse des erreurs causées par l'utilisation de méthodes simplifiées pour calculer l'ingestion de nourriture à partir de contenus stomacaux chez les poissons. Nous avons examiné trois sources d'erreur, soit les conséquences (1) d'estimer la consommation à partir d'un petit nombre de prélèvements de contenus stomacaux, (2) d'utiliser des contenus stomacaux moyens obtenus par le regroupement de prélèvements, plutôt que des prélèvements individuels et (3) de ne pas tenir compte des facteurs biologiques qui affectent l'évacuation des proies. Dans une étude de simulation, l'estimation de la consommation à partir de seulement deux prélèvements stomacaux a donné des résultats proches de l'ingestion réelle. En revanche, l'estimation de l'ingestion de nourriture à partir de prélèvements stomacaux regroupés introduit une erreur positive importante. Nous fournissons une correction qui peut servir à rectifier cette erreur dans l'analyse. Nous suggérons une nouvelle méthode, qui tient compte de la répartition et de l'évacuation des divers types individuels de proies, ainsi que de l'effet de la présence d'autres aliments dans l'estomac sur l'évacuation, pour estimer l'ingestion particulière des différents types de proies. La simplification de l'estimation par la négligence de ces facteurs produit une erreur dans la consommation estimée de proies individuelles pouvant atteindre 150 % dans un exemple basé sur des données réelles.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: December 1, 2004

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  • Published continuously since 1901 (under various titles), this monthly journal is the primary publishing vehicle for the multidisciplinary field of aquatic sciences. It publishes perspectives (syntheses, critiques, and re-evaluations), discussions (comments and replies), articles, and rapid communications, relating to current research on cells, organisms, populations, ecosystems, or processes that affect aquatic systems. The journal seeks to amplify, modify, question, or redirect accumulated knowledge in the field of fisheries and aquatic science. Occasional supplements are dedicated to single topics or to proceedings of international symposia.
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