A bioenergetic model for estimating the food requirements of Steller sea lions Eumetopias jubatus in Alaska, USA

Abstract

A generalized bioenergetic model was used to estimate the food requirements of Steller sea lions Eumetopias jubatus in Alaska, USA. Inputs included age-and sex-specific energy requirements by date, population size and composition, and diet composition and energy content. Error in model predictions was calculated using uncertainty in parameter values and Monte Carlo simulation methods. Our model suggests that energy requirements of individuals were generally lowest in the summer breeding season (June to August) and highest in the winter (December to February) and spring (March to May) mainly due to changes in activity budgets. Predicted relative daily food requirements were highest for young animals (12 ± 3% SD and 13 ± 3% of body mass for 1 yr old males and females respectively) and decreased with age (5 ± 1% and 6 ± 1% of body mass for 14 yr old males and 22 yr old females respectively). The mean daily food requirement of pregnant females predicted by the model was only marginally greater than the predicted mean daily food requirement of non-pregnant females of the same age. However, the model suggested that the mean daily food requirement of females nursing pups was about 70% greater than females of the same age without pups. Of the 3 sets of model parameters (diet, population, and bioenergetic), uncertainty in diet and bioenergetic parameters resulted in the largest variation in model predictions. The model provides a quantitative estimate of the Steller sea lion population's food requirements and also suggests directions for future research. KEY WORDS: Bioenergetic model · Eumetopias jubatus · Food consumption · Steller sea lion · Sensitivity analysisResale or republication not permitted without written consent of the publisher Mar Ecol Prog Ser 229: 291-312, 2002 third method for estimating food consumption is bioenergetic modeling.Biological systems are governed by the laws of thermodynamics and theoretically reach steady states where energy influx is equal to energy efflux (Wiegert 1968, Galluci 1973. In reality, a true steady state is never reached in nature, but in the long term any biological system must be in energy balance such that Consumption = Feces + Urine + Respiration + Productionwhere 'Consumption' is energy ingested, 'Feces' and 'Urine' are energy egested, 'Respiration' is energy used for work (degraded to heat), and 'Production' is energy deposited as tissue growth, fat storage, eggs, sperm, embryos, exuviae etc. (Klekowski & Duncan 1975). The energy consumption of marine mammals has frequently been estimated using bioenergetic models (Hinga 1979, Naumov & Chekunova 1980, AshwellErickson & Elsner 1981, Doidge & Croxall 1985, Hiby & Harwood 1985, Lavigne et al. 1985, Worthy 1987a, Härkönen & HeideJørgensen 1991, Markussen & Øritsland 1991, Ryg & Øritsland 1991, Markussen et al. 1992, Olesiuk 1993, Ugland et al. 1993, Mohn & Bowen 1996). These models range in detail from simple equations (with few parameters) representing an average individual's annual energy consumption, to detai...

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