Weddell seal pup mass (weight) at weaning is important to seal survival, and is an essential measure of maternal investment by Weddell moms in their pups.  Weddell moms usually fast during the 5 to 6 week nursing period.  And for every pound a pup gains during the nursing period, the mother can lose around 2 lbs of her own body mass.  Weddell pups can more than triple their birth weight before being weaned, so there is a very large transfer of energy from mom to pup during this nursing period.

The Weddell seal population and mass dynamics project has published a number of research papers to date on Weddell seal reproductive costs and the relationship of pup mass to seal survival.  The researchers continue to learn more every year about this long-lived apex predator and how it interacts with its changing Antarctic environment.

A crucial part of the Weddell seal research team's field work involves weighing pups at 3 different stages during the 5 to 6 week nursing period, with the first weighing taking place a day after birth, a second weighing around the mid-nursing period at 20 days, and a third weighing near weaning at around 35 days.  The 35 day pup weights range from around 150 to 280 lbs (68 to 127 kg).  In the images below, field researchers weigh a large pup as the mom looks on.

Also during the 35 day weighing, researchers will retrieve temperature tags from those pups that received the small temperature sensor/recorders.  "Out of the 57 temperature tags we deployed on pups this year, we have successfully recovered 16 so far.  We know that three of the tags have been lost, so we are crossing our fingers for getting the remaining 38 by the end of the season," says field researcher Jesse DeVoe.

In the image above, data from one of the small temperature recorders is displayed in graph form.  Because sea water temperature under the ice is a constant -1.8° C (28° F) but the surface temperatures on top of the sea ice can vary widely, researchers are able to deterimine when pups are in the water based on the data recorded by the temperature tags.  DeVoe notes, "The data retrieved so far shows lots of swimming pups!"

– Mary Lynn Price

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