Scripps Institution of Oceanography

Annual diving patterns in pinnipeds are difficult to study because most seals and sea lions are at sea and inaccessible for a large portion of the year. Consequently, until recently, most studies of pinniped biology were concerned with the onshore behavior of species that breed in accessible sites. Of all the species studied, however, the Weddell seal (Leptonychotes weddellii) presents a remarkable exception to the generally incomplete view of the natural history of marine mammals. The south polar, fast ice environment of Weddell seals provides an unparalleled opportunity for diving studies. Because Weddell seals regularly haul out onto the sea ice surface, investigators can approach the seals whenever sea ice is present. As a result, it is possible to study adult males, females, and sub-adults at different times in their life cycles and examine their breeding success and population movements. We present information collected during six field seasons, including a full year study in 1981. The goal of this project was to examine how behavioral responses to diving in the Weddell seal vary with season and location. In order to correlate diving behavior with seasonal or geographical variations, it is necessary to discuss the seals' environment. This includes not only the physical environment above and below the sea surface, but also how the seals may navigate and hunt under those conditions and what prey would be available. The following sections describe the study sites and examine the navigation abilities and feeding habits of the seals. By reviewing this information first, the reader will have a better understanding of some of the factors that may influence the diving patterns that are reported later.