The effects of variability in Antarctic krill ( Euphausia superba) spawning behavior and sex/maturity stage distribution on Adélie penguin ( Pygoscelis adeliae) chick growth: A modeling study

Factors that control variability in energy density of Antarctic krill ( Euphausia superba) populations, and the consequences of this variability for growth and fledging mass of Adélie penguin ( Pygoscelis adeliae) chicks, were investigated using an individual-based energetics model. Lipid content as a function of sex/maturity stage and season was used to calculate the energy density of krill ingested by chicks. Simulations tested the influence of variability in krill size-class distribution, sex-ratio, length-at-maturity, and the timing of spawning on krill population energy density and penguin chick fledging mass. Of the parameters included in simulations, variability in the timing of krill spawning had the greatest influence on predicted Adélie penguin fledging mass, with fledging mass decreasing from 3.30 to 2.92 kg when peak spawning was shifted from early December to early March. Adélie penguin chicks that fledge from colonies along the western Antarctic Peninsula (wAP) and survive to recruit into the breeding population are 0.117 kg heavier than those that do not survive to breed. Thus, it appears that small differences in fledging mass potentially have significant implications for Adélie penguin chick survivorship. Therefore, the timing of krill spawning may have important consequences for Adélie penguins, and other top-predator species, that may time critical activities to coincide with a period of dependable prey availability with maximum energy density.