Estimating fine-scale energy expenditure

Estimating fine-scale energy expenditure in wild California sea lions: effects of foraging strategy? (In collaboration with Drs. Colin Ware, Liz McHuron, Dan Costa, and Gitte McDonald).

Foraging animals expend metabolic energy on the locomotion used to find and capture prey. While lactating California sea lions use a variety of foraging strategies to maximize their (acquired energy : expended energy) ratio, each strategy involves leaving the pup at a rookery for several hours to several days at a time while hunting for prey at sea. If too much energy is spent compared to energy acquired in the form of food, the impact may be seen at a variety of scales. If too little energy is ingested, an animals will catabolize its own tissues – usually blubber energy stores – leading to poor body condition among other problems. Furthermore, sea lions struggling to find enough energy have been shown to alter their behavior – searching deeper in the sea, further from the rookery, and for longer duration – to try to find enough energy. An individual who cannot sustain herself and her pup will be forced to wean the pup early, usually spelling disaster for the pup. In years with bad oceanographic and prey conditions, the effect of many sea lions struggling to find energy often manifests as greatly increased reproductive failure at a population level.

Many logical links in this system are well-studied; however, the effect of foraging strategy on energy expenditure amounts to something of a knowledge gap. California sea lions are known to have high inter-individual differences in foraging strategy. Beyond this, each individual is quite likely to use multiple foraging strategies. However, as oceanic systems and prey distributions will inevitably change with the planet’s climate in coming decades and centuries, a key piece of the puzzle will be an understanding of how (if at all) foraging strategy affects energetic acquisition:expenditure ratios.

Dataloggers sensing movement (acceleration, compass bearing, rotational velocity) have been used to estimate activity in pinnipeds – as a proxy for, or correlate of, metabolic energy expenditure – for years. Recently, an accelerometer- and gyroscope-based measurement called APBA has been developed with related Steller sea lions (Eumetopias jubatus) as a close approximate of metabolic energy expenditure. In this project, I hope to compare the effect of foraging strategy on fine-scale energy expenditure, both within and between individuals.