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

Abstract

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 stomach contents derived from pooled stomach samples rather than individual stomachs and (3) the effect of ignoring 5 biological factors which affect the evacuation of prey. Estimating consumption from only two stomach samples provided results close to the actual intake rate in a simulation study. In contrast to this, serious positive bias was introduced by estimating food intake from the contents of pooled stomach samples. An expression is given which can be used to correct analytically for this bias. A new method which 10 takes account of the distribution and evacuation of individual prey types as well as the effect of other food in the stomach on evacuation is suggested for the estimation of the intake of separate prey types. Simplifying the estimation by ignoring these factors biased consumption estimates of individual prey by up to 150% in a data example. 15

Influence of food quality on lipids and essential fatty acids in the body of the Black Sea sprat Sprattus sprattus phalericus (Clupeidae)

“…(Rindorf and Lewy, 2004), whereas the content of storage lipids (TAGs) in the fish body at the end of the feeding period is an integral characteristic of fish food supply for the entire feeding period (Shul'man, 1974). In 2006 and 2010-2011, when the level of the analyzed lipids was low, the sprat stomach contents consisted primarily of remains of small eurythermal and warmwater planktonic organisms, such as Acartia, Paracalanus, Oithona spp., Oikopleura, bivalve larvae, nauplii, and early copepodite stages of Calanus (Fig.…”

Diet estimation of Paralichthys orbignyanus in a coastal lagoon via quantitative fatty acid signature analysis

“…These methods usually reflect the last food intake, several times inferring the diet from the identification of parts of hard tissues or remainders of skeletons and the occurrence of empty stomachs is common (Hyslop, 1980;Rindfort and Lewy, 2004). Alternatively the robustness of QFASA is associated with its capacity to detect small prey even reflecting the food intake from the previous weeks.…”

Diet of Double-Crested Cormorants (Phalacrocorax Auritus) Wintering on the Central Texas Coast

“…For ecosystem modeling, reporting diet composition in terms of %W is critical since many ecosystem models are based on mass-balance approaches (e.g., Ecopath; Christensen et al 2008). However, this method does have its challenges because the physical separation of different prey types is often difficult due to differential digestion rates (Baker et al 2014), the order of prey ingestion, prey handling, and evacuation rates (Rindorf and Lewy 2004;Baker et al 2014). Empirical relationships have been developed to convert %FO to relative weight composition based on samples obtained outside of the GOM (Stobberup et al 2009), but this is an approximation and should only be used in the absence of more direct measurements.…”