Intellectual Merit: Weddell seals (Leptonychotes weddellii) locate and capture sparsely distributed and mobile prey under shore-fast ice throughout the year, including the austral winter when ambient light levels are very low and access to breathing holes is highly limited. This is one of the most challenging environments occupied by an aquatic mammalian predator, and it presents unique opportunities to test hypotheses concerning: 1) behavioral strategies and energetic costs for foraging and 2) sensory modalities used for prey capture under sea ice. To accomplish these objectives, we will attach digital video and data recorders to the backs of free-ranging Weddell seals during the autumn, winter and early spring. These instruments simultaneously record video of prey pursuit and capture and three-dimensional movements, swimming performance, ambient light level and other environmental variables. Energetic costs for entire dives and portions of dives will be estimated from stroking effort and our published relationship between swimming performance and energetics for Weddell seals. The energetic cost of different dive types will be evaluated for strategies that maximize foraging efficiency, range (distance traveled), and duration of submergence. The proposed study will provide a more thorough understanding of the role of vision and changing light conditions in foraging behavior, sensory ecology, energetics and habitat use of Weddell seals and the distribution of encountered prey. It also will provide new insights into survival strategies that allow Weddell seals to inhabit the Antarctic coastal marine ecosystem throughout the year.
Broader Impacts: The proposed study will train two graduate students and a Post-doctoral Fellow. Outreach activities will include interviews, written material and photographs provided to print and electronic media, project web sites, high school email exchanges from McMurdo Station, hosting visiting artists at our field camp, and public lectures. We will provide a weekly summary of our research findings to teachers and students in elementary school programs through our websites, one of which received an educational award. Our previous projects have attracted an extraordinary amount of press coverage that effectively brings scientific research to the public. This coverage and the video images generated by our work excite the imagination and help instill an interest in science and wildlife conservation in children and adults.
Intellectual Merit. Weddell seals live and forage beneath the shore-fast ice in McMurdo Sound and elsewhere around the Antarctic continent year round. This is one of the most challenging environments inhabited by an air-breathing mammal, and we are just beginning to understand the behavioral and physiological adaptations that enable Weddell seals to survive and thrive. We tested specific hypotheses related to general foraging strategy, foraging location, searching mode, prey detection, locomotory performance, the energetic cost of diving and digestion, and foraging efficiency, with special attention to differences in these traits related to seasonally varying surface light intensity (winter vs. spring). Three dive types were identified in winter dives, and they clustered in a similar pattern in the discriminant analysis for spring dives during a period of continuous light. Most prey (98%) captures occurred in only one of the dives types (Type 1), and the primary (99%) prey was Antarctic silverfish (Pleuragramma antarcticum). Although there were some statistically significant differences between spring and winter dives, overall they were very similar. During the spring and winter, seals use a similar diving strategy for hunting, guarding breathing holes, and transiting which may reflect both physiological and behavioral constraints associated with the need to breathe periodically at widely spaced ice holes. We examined foraging dives (Type 1) separately from all other types of dives to determine how hunting behavior varies with seasonal changes in photoperiod and surface light intensity. We found that the mean maximum depth of spring foraging dives was significantly greater than winter foraging dives, as would be expected if seals used vision to locate prey because the greater light intensity during spring would penetrate to greater depths. Examining this at a finer level, mean maximum dive depth decreased with increasing solar angle during the winter, but increased with increasing solar angle during the spring. We found that foraging effort is concentrated during the light phase (specifically, local noon) in winter dives, which supports use of vision in hunting. However, foraging effort was not uniformly distributed during spring, as would be expected during a period without a dark phase. Foraging success was not significantly greater during winter light phase than spring dark phase, but it was greater during spring than during winter dark phase. Metabolic measurements were made for each of the 15 seals during this study and compared to seals measured previously during the spring and summer. Evaluation of swimming performance (stroking frequency, speed, tortuosity of fish chases, distance for fish chases) indicate behavioral "pacing" by foraging seals through changes in preferred stroking gait when encountering different types of prey. Three dimensional dive profiles showed a saw-tooth pattern of performance levels consisting of low speed, gliding descents followed by high speed, high stroke frequency ascents when capturing Antarctic silverfish. More directed pursuit occurred for benthic prey and larger species. Hunting strategies depended on the depth of prey encounters. In general, hunting effort became more conservative in terms of energetic expenditure as the duration of the dive progressed. As the seals ascended from depth, foraging intensity (based on distance of prey chases, tortuosity of the chase path) decreased resulting in a reduction in the cost of predation for shallower fish encountered late in a dive. The magnitude of these patterns is modified according to the changes in dive types and season as described above. Broader Impacts. We trained five graduate students, and one student completed a master’s degree in Education and is pursuing a career in public outreach and K-12 education for marine studies. We have conducted interviews with secondary school students, provided written material and photographs, and given lectures to undergraduate and graduate students. With a graduate student in Education on our project (B. Richter), we have developed lesson plans for K-12 science teachers that have been posted online and now are used in museum education programs. An interactive website was developed for this project and distributed to schools nationally and internationally through the National Marine Educators Association. School children and teachers throughout the United States and New Zealand have used the site for classroom studies on the Antarctic and global climate change. Results from our research excite the imagination and help instill an interest in science in children and adults. Lastly, with growing concern about climate change in polar regions by both scientists and the public, this study and the video images collected will provide a unique "seal’s eye view" of the current environmental challenges of Antarctic species that should be of broad appeal.
