Diet Composition, Reproductive Energetics, and Productivity of Seabirds Damaged by the Exxon Valdez Oil Spill

Abstract

Piscivorous predators can experience multi-fold differences in energy intake rates based solely on the types of fishes consumed. We estimated energy density (kJ/g) of 1,311 fish from 32 species by proximate analysis for lipid, water, ash-free lean dry matter, and ash contents and evaluated factors contributing to its variation. Lipid content was the primary determinant of energy density, ranging from 2 to 61% dry mass and resulting in a 5-fold difference in energy density of individuals (2.0-10.8 kJ/g wet mass). Energy density varied widely within and between species. Schooling pelagic fishes had relatively high or low values, whereas nearshore demersal fishes were intermediate. Pelagic species maturing at a smaller size had higher and more variable energy density than pelagic or nearshore species maturing larger. High-lipid fishes had less water ('10 wet mass) and more protein (% lean dry mass) than low-lipid fishes. In some forage fishes, size, month, reproductive status, or location contributed significantly to intraspecific variation in energy density. Differences in quality may affect diet selection of breeding seabirds especially, as they must transport food for their young from foraging area to nest site.