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Crabeater seals foraging in the Antarctic Winter
Project Summary:
Within the Southern Ocean, marine coastal and pelagic environments are characterized by seasonally high productivity that supports large numbers of breeding marine predators. However, in contrast to early work which suggested that primary productivity was unusually high and the food chains short, robust, and highly efficient, more recent work has suggested both that the overall levels of primary productivity are lower, and that food webs are more complex. In addition, it has become clear that the Antarctic marine environment experiences considerable inter- and intra- annual variability. Consequently, available prey resources for vertebrate predators can be both spatially and temporally patchy. In the face of such unpredictability, most marine predators appear to rely on oceanographic features, such as frontal systems, thermocline depth, and bathymetry to concentrate or aggregate their prey in such a way to enable effective foraging. However, while the importance of these physical features has long been recognized, the interactions between environmental features, prey abundance, and predator distributions and foraging strategies are only poorly understood.
Crabeater seals offer a unique opportunity to better understand the foraging strategies utilized by marine predators in the face of meso- and fine-scale ecological variability. Within the seasonal pack ice zone crabeater seals prey almost exclusively on Antarctic krill (Euphausia superba). Yet despite their reliance on a locally abundant and spatially heterogeneous prey resource, crabeater seals are the most abundant Antarctic pinniped (c. 15 million). Thus, the crabeater seals have clearly evolved behavioral patterns that are optimized to exploit prey that are patchily distributed within both space and time. Therefore we predict that studying how crabeater seals are dispersed within and below the seasonal pack ice will likely reveal those specific strategies used by seals to optimize foraging success. Two such strategies include the close proximity of haul-out and foraging sites, and the reliance on environmental features to aggregate their select prey. Therefore this work will focus on understanding what aspects of ocean structure are correlated with specific behaviors, identifying how dependent seals are on these oceanographic features to concentrate prey, and determining how crabeater seals optimize their behavior to accommodate seasonal or annual fluctuations in oceanographic features and the distribution of prey.
Specifically, this project will determine the distribution and foraging behavior of adult female crabeater seals (Lobodon carcinophagus), and simultaneously assess the impact that oceanographic features and prey aggregations have on the foraging strategies employed. To do so, we will use a combination of satellite-linked tracking, specialized dive recorders, isotopic tracers, and concurrently and/or remotely collected information on the distribution and abundance of krill. In particular, this project will test the following hypotheses: 1) that foraging locations are correlated with environmental features known to influence krill abundance; 2) that seasonal shifts in foraging behavior track krill movement patterns; and 3) that crabeater seal foraging behavior conforms to that predicted by optimality models.
In addressing these hypotheses, this research will enable us to link biological (prey composition, distribution, and abundance) and physical characteristics of the foraging environment with the foraging behavior and strategies of a free-ranging marine vertebrate predator. Because crabeater seals are the most abundant pinniped in the Antarctic, their foraging activities undoubtedly have a large impact on the Antarctic marine ecosystem. Therefore, understanding both how crabeater seals select their foraging locations and prey, and how alterations in environmental conditions and krill abundance may impact crabeater seals is essential to our understanding of Antarctic ecology.
This research project is part of the Southern Ocean Global Ocean Ecosystems Dynamics Program (SO GLOBEC), which is designed to elucidate shelf circulation processes and their effect on sea ice formation and Antarctic krill (Euphausia superba) distribution, and to examine the factors that govern krill survivorship and availability to higher trophic levels, including seals, penguins and whales. These goals are approached through a moored instrument program, broad-scale physical, biological, and chemical oceanographic surveys, process-oriented investigations, and modeling studies focused on austral winter processes in the region west of the Antarctic Peninsula.
There are many different research teams and two research vessels participating in this cruise. A list of participants can be found here.
Marguerite Bay is the center of the study area along the Antarctic Peninsula (68'S, 69'W).The continent is outlined in green, and is largely covered by clouds to the East. Open water is black, and we are hoping to see more sea ice in the study area soon. More maps of the study area and the boat cruise track can be found here.
Last revised: March 20, 2003