Foraging Behavior Of Key Antarctic Predators Unchanged After Storms That Alter Prey Distribution

The team’s research shows that the spatial distribution of fur seals and foraging chinstrap penguins did not change after a near gale, despite substantial changes in the abundance and distribution of their prey, Antarctic krill.

“In order to better understand how energy moves through an ecosystem, we need to have a better understanding of how predator-prey interactions are affected by environmental conditions,” said Dr. Warren. “The storm that occurred between our two ship-based surveys created a perfect ‘natural experiment’ which allowed us to take ‘before’ and ‘after’ measurements and examine how the nearshore ecosystem north of Livingston Island Antarctica was affected by the winds and waves.”

Antarctic krill are 1-2 inches long crustaceans that play a critically important role in the ecosystem because so many other animals rely on krill as their primary food source. Dr. Warren and colleagues found that the storm reduced the concentration of krill in their study area to roughly half what it was before the storm, likely because currents pushed the krill off shore. They also observed that after the storm, krill were found in different geographic areas within the study site.

When Antarctic krill abundance decreased in certain areas after the storm, Dr. Warren and colleagues found that feeding aggregations of cape petrels, which are flying seabirds that eat krill, also decreased in those areas. However, other krill predators did not change their foraging behaviors in response to changes in krill distribution. Chinstrap penguins, which are swimming seabirds, and fur seals, which are marine mammals, both showed little change in their distribution after the storm.

“Relative to cape petrels, penguins and fur seals may not be as dependent on finding prey over small time scales due to their longer foraging-trip length and energy-storage capacity,” said Dr. Warren. “If the changes due to a storm are relatively short-lived, penguins and seals may not need to alter their habits and can stick to their familiar feeding areas.”

This research was funded by the National Science Foundation's Office of Polar Programs and the National Oceanic and Atmospheric Administration's Antarctic Marine Living Resources program. The study's co-authors are Jarrod A. Santora (City University of New York, now at the Farallon Institute for Advanced Ecosystem Research) and David A. Demer (NOAA, National Marine Fisheries Service, Southwest Fisheries Science Center).