An 11 year old male Weddell seal on the sea ice at the nearshore Hutton Cliffs pupping colony.
Photo by Parker Levinson.
Two recent scientific papers by the project published this year and last, provide some new fascinating insight into the lives of male Weddell seals. A great recent article about the findings of these papers can be found in The Antarctic Sun. Yet the study of male Weddell seals is not new to the Weddell seal population project.
Although much of the Weddell seal population study's work has been on Weddell moms and pups over the more than 50 years of the project's existence, Weddell males were initially studied in the late 1960s by scientists Don Siniff, Ian Stirling, and others. (Please read more on the project's history here.) In the 1970s when the project was based at the University of Minnesota and headed by Don Siniff (Co-PI of the current Weddell seal population study now based at Montana State University), the research then focused on male Weddell underwater behavior and territorial defense. In fact, the only currently known underwater film of Weddell seal mating was obtained during this time!
1969 photo of TV camera with 360 degree rotor used to film only known footage of Weddell seals mating underwater.
Photo courtesy of the archives of Dr. Don Siniff.
In 1973 it was determined that studying various aspects of Weddell seal behavior would benefit substantially by following the same seals over multiple years, and soon after the seasonal tagging of all of the seals in the study area was initiated and continues to this day. Currently, the field researchers identify and record all of the Weddell seal pups born in the Erebus Bay study area each pupping season, male and female. The researchers also make several surveys during the season to determine how many seals are in the entire Erebus Bay study area during that pupping season, and who they are.
Beginning in the late 1990s, male and female genetic samples were also obtained annually by the field research team, and are used for Weddell genetic studies by Dr. Tom Gelatte and others. A very recent paper that our research group helped with has evaluated methods for pedigree construction using genomics methods and samples collected from our study population and a nearby genetically isolated population of Weddell Seals (Miller et al. 2021). These genetic studies help researchers understand how individual Weddell males contribute to the composition of this Weddell population.
Another male Weddell seal, also at Hutton Cliffs pupping colony. Photo by Parker Levinson.
Two scientific papers that our research group recently published about male Weddell seals give interesting insight into the lives and contributions of male Weddells (Brusa et al. 2020, Brusa et al. 2021). The first of those papers provides evidence that like females, male Weddells also suffer declines in their probabilities of surviving from one year to the next as they age. Further, it appears that males don’t typically live as long as females do. Such a pattern suggests that males also likely incur reproductive costs that reduce their survival. Male-male contests and male territorial defense behavior likely take a toll on Weddell males as soon as they become reproductively active, and this continues throughout their lives. The second of the papers investigated where males of different ages tend to show up in different locations in our study area relative to where large groups of mother-pup pairs tend to be found. Weddell males that were at prime breeding ages tend to show up in more crowded nearshore colonies where there are more high-quality prime-age reproductive females. Younger males and very old males tend to be found more often in less-crowded offshore pupping colonies where there are fewer large, high-quality females of prime pupping age.
The great benefit of this long-term Weddell seal research project is that we now have reproductive and genetic data on numerous generations of Weddell seals, male and female. So we are now better able to understand how individual seals of both genders survive, live, reproduce, and contribute to the dynamics and stability of the overall general population of Weddell seals in Erebus Bay. This in turn can help us better understand the possible effects of climate change and environmental changes on Weddell seals, and possibly other species of long-lived marine mammals.
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