WEDDELL SEAL POPULATION DYNAMICS RESEARCH
The Ross Sea, a geographically well-defined embayment of the Antarctic continental shelf, provides an outstanding scientific opportunity in the Southern Ocean for gaining insights into marine ecosystem processes due to its unique combination of attributes. Of note, the Ross Sea is one of the most pristine marine systems on the planet. An intensive study of a breeding population of Weddell seals in the Erebus Bay region of eastern McMurdo Sound at the southern extent of the Ross Sea was initiated in 1968. The study of this population represents one of the longest continuous field investigations of a long-lived mammal in existence. Because Weddell seals are large, marine predators, information on the population provides an excellent complement to other studies on other aspects of the marine system (for example, studies of penguins, fish, and marine invertebrates). Further, the long-term data for Weddell seals provide a valuable benchmark for monitoring potential changes in the future. This is especially valuable given interests in potential effects of climate change and possible effects of recently established fishing operations in the area.
For nearly 50 years of this study, more than 24,150 animals have been tagged to date, and over 241,036 re-sightings have been logged in the database. Emphasis has consistently been on maintaining and enhancing annual demographic data through the use of mark-resight techniques. Because all pups born within the study area have been tagged since 1973 and because this species demonstrates strong philopatric behavior, approximately 80% of the seals are marked and more than 65% of the individuals in the population are currently both marked and of known age.
This study and the database accrued over 46 years of intensive effort provide a strong foundation and unique opportunity to extend our ecological knowledge of population and ecosystem processes. Inferences from this multi-decadal study extend beyond the Ross Sea and contribute to a broader body of knowledge about the evolution of life-history strategies and population dynamics of long-lived organisms in variable environments. Such information is vital to understanding and conserving many other animal populations. In our current work we continue to build on this foundation with two lines of investigation that combine (1) mark-resight and other advanced analytical tools to describe and understand population processes and (2) studies of seal mass dynamics to link demographic variability with ecosystem processes.
To meet the objective of our current research agenda and to test the hypotheses of primary interest, we use a variety of approaches and methodologies that can be categorized into three general initiatives: 1) continuation of annual seal tagging and mark-resight surveys to maintain continuity of the long-term demographic database, 2) comprehensive analyses and integration of the long-term demographic database using recently developed analytical approaches, and 3) collection and analyses of individual body mass dynamics and the development of multiple regression models to evaluate the hypotheses posed.
Data on animals tagged through the end of the 2015 Weddell seal pupping season can be downloaded here. The data can be used to obtain information on:
1. Individual tag information including the most recent tag numbers and colors,
2. Year when each animal was tagged,
3. Animal sex,
4. Animal age when tagged (for animals tagged as pups, age can be calculated), and
5. Date the animal was last observed.
If you have questions about the project or seal database, please contact Jay Rotella or Bob Garrott by e-mail, surface mail, or phone.