Research Objectives:
The Erebus Bay Weddell seal (Leptonychotes weddellii) population study in eastern McMurdo Sound was initiated in 1968 and represents one of the longest intensive field investigations of a long-lived mammal in existence. Over nearly 35 years, a total of 15,636 animals have been tagged, with 144,927 resighting records logged in the database. This study is a valuable resource for understanding population dynamics not only of Weddell seals, but also of other species of both terrestrial and marine mammals. Project team members will continue two lines of investigation that combine the long-term database with new field initiatives.
The continuity of the demographic data will be maintained by annually marking all pups born, replacing lost or broken tags, and performing censuses. Researchers will combine the new data with the existing database and perform a progressively complex series of demographic analyses that will allow testing of specific hypotheses about population regulation and evaluate previously determined temporal and spatial patterns of variation in vital rates among colonies.
The primary new field initiative will involve an intensive study of mass dynamics of both pups and adult females to assess annual variation in marine resources and their potential role in limiting or regulating the population. In addition to collecting data on body mass dynamics, investigators will use satellite imagery to develop an extended time-series of sea ice in McMurdo Sound. (Regional extent of sea ice affects both regional primary productivity and availability of haul-out areas.) Increased primary productivity may increase marine resources, which would be expected to have a positive effect on foraging efficiency, leading to increased body mass.
Understanding the mechanisms that limit or regulate Weddell seal populations and the specific linkages between climate, oceans, ice, and antarctic food webs can make important contributions to knowledge of pinniped population dynamics, as well as theoretical understanding of populations, communities, and ecosystems.
Such knowledge can be readily applied to enhance the ability of natural resource managers to effectively maintain assemblages of other large mammal species and the ecological processes they facilitate. Continuation of this long-term study may also contribute to understanding the potential impacts of human activities such as global warming and the commercial exploitation of antarctic marine resources.
A field camp will be established at Big Razorback Island and all pups born in the eight colonies that make up the Erebus Bay population will be tagged, with a smaller effort to tag adults encountered that have not been tagged previously. The entire population will be censused seven to eight times after the pupping season. In addition, seals (both adults and pups) will be weighed and photographed from several perspectives using digital camera systems to develop methods to predict the mass of seals based on body morphometrics obtained from the photographs.
A large sample of seals will be photographed throughout the field season to document body mass dynamics of pups and adult females. These data will be correlated with a variety of variables including sea ice condition, colony, age, time of year, survival, and reproduction to understand the role of climate, local colony, and individual characteristics on both mass and population dynamics. A sample of study animals may be outfitted with data recorders to examine correlations between foraging, body mass, and breeding success. Data on health (physical exams and hematological and serum biochemical analyses, etc.) of these and other seals will also be collected. Scat and blubber biopsy samples will be collected to document diet.
