How much food do Steller sea lions need?

A number of different approaches have been taken to estimate the amount of food consumed by marine mammals in the wild. One is to estimate it from the amount of food fed to marine mammals in captivity. Another is to kill marine mammals in the wild and measure the amount of food in their stomachs. Neither of these approaches is very satisfactory.

A third method is to estimate consumption using mathematical equations that consider the amount of energy required to grow, swim and reproduce. The equations must also consider the energy content of different prey, and the efficiency with which animals can extract energy from different prey. We refer to this series of mathematical equations as a bioenergetic model.

Arliss Winship (along with his collaborators Dr. Andrew Trites and Dr. David Rosen) developed a bioenergetic model for the Steller sea lion. Much of the information that went in to the model was from experiments conducted with our captive sea lions at the Vancouver Aquarium. Our model predicts the amount of prey consumed by individual Steller sea lions of different ages and sexes, as well as the amount of prey consumed by the entire population of Steller sea lions in Alaska.

Graph Showing Differences in Food Consumption

The model predicted that Steller sea lions require the least amount of energy during the summer breeding season (June - August) and the highest amount during winter (December - February) and spring (March - May). This is largely because sea lions are more active during winter and spring than at other times of the year (i.e., they swim more and go on longer trips).

Relative to body size, young sea lions require about twice as much food compared to older individuals. For example, a one-year-old female needs 13% of her body mass in food each day, compared to a mature female that only needs an average of 6%.

Our model suggested that pregnancy does not cause a large increase in food requirements, but that a female nursing a pup must consume about 70% more prey on average than a non-nursing female to produce milk for her pup.

An important consideration with computer models is how accurately do they represent the real world? In other words, how much uncertainty is there in the model predictions? We found uncertainty in some of our predictions that can be reduced by further studies on the diet and physiology of Steller sea lions.

Further details about this study are contained in Winship et al. (2002).

(2002).

24 April 2002