Patterns and Processes: Dynamics of the Erebus Bay Weddell Seal Population
The Erebus Bay Weddell seal population study in eastern McMurdo Sound, Antarctica was initiated in 1968 and represents one of the longest intensive field investigations of a long-lived mammal in existence. Over the thirty-four year period of this study a total of 15,636 animals have been tagged with 144,927 re-sighting records logged in the current database. As such, this study is an extremely valuable resource for understanding population dynamics of not only Weddell seals, but also other species of both terrestrial and marine mammals with similar life-history characteristics. With the retirement of the original investigator, Dr. Donald Siniff, this proposal represents an effort to transition the long-term studies to a new team of investigators. Dr. Robert Garrott and Dr. Jay Rotella propose building upon the foundation with two lines of investigation that combine use of the long-term database with new field initiatives. The continuity of the demographic data will be maintained by annually marking all pups born, replace lost or broken tags, and perform multiple mark-recapture censuses of the Erebus Bay seal colonies. The new data will be combined with the existing database and a progressively complex series of analyses will be performed using recently developed mark-recapture methods to decompose, evaluate, and integrate the demographic characteristics of the Erebus Bay Weddell seal population. These analyses will allow the testing of specific hypotheses about population regulation as well as temporal and spatial patterns of variation in vital rates among colonies within the population that have been posed by previous investigators, but have not been adequately evaluated due to data and analytical limitations. The primary new field initiative will involve an intensive study of mass dynamics of both pups and adult females as a surrogate measure for assessing annual variation in marine resources and their potential role in limiting and/or regulating the population. In conjunction with the collection of data on body mass dynamics the investigators will use satellite imagery to develop an extended time series of sea ice extent in McMurdo Sound. Regional extent of sea ice affects both regional primary productivity and availability of haul out areas for Weddell seals. Increased primary productivity may increase marine resources which would be expected to have a positive affect on Weddell seal foraging efficiency, leading to increased body mass. These data combined with the large proportion of known-aged seals in the current study population (>60%) will allow the investigators to develop a powerful database to test specific hypotheses about ecological processes affecting Weddell seals. Knowledge of the mechanisms that limit and/or regulate Weddell seal populations and the specific bio-physical linkages between climate, oceans, ice, and Antarctic food webs can provide important contributions to understanding of pinniped population dynamics, as well as contribute more generally to theoretical understanding of population, community, and ecosystem patterns and processes. Such knowledge can be readily applied elsewhere to enhance the ability of natural resource managers to effectively maintain assemblages of other large-mammal species and the ecological processes that they facilitate. Continuation of this long-term study may also contribute to understanding the potential impacts of human activities such as global climate warming and the commercial exploitation of Antarctic marine resources. And finally, the study can contribute significantly to the development and testing of new research and analytical methodologies that will almost certainly have many other applications.
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