For the past several seasons, the number of Weddell seal pup births in the Erebus Bay study area has been at Weddell seal population study record levels. This population study has been underway for nearly 50 years, making it one of the longest running population studies ever of a long-lived mammal. This National Science Foundation funded population project work has resulted in a multi-generation Weddell seal database that is unique in the scientific community.
"We’re up to approximately 500 pups as of this evening, and ought to be at about the peak. With the ice edge less than 2 miles away, we are also seeing quite a few emperor penguins this season," reports project lead scientist Dr. Jay Rotella.
Since 1973 the Weddell seal population study field teams have marked and recorded over 23,571 seals. They have recorded over 241,036 re-sightings of those marked seals. Over 80% of the Weddell population in the Erebus Bay study area have been marked and recorded. And over 80% of the marked Weddell population consists of known-age seals, meaning those seals that were originally marked at birth, and their mothers known and recorded.
The number of Weddell pup births in the Erebus Bay area has fluctuated from record lows in the last decade when the infamous massive Iceberg B-15 blocked access to Weddell pupping colonies, resulting in the lowest pup birth number in the study's recorded history which occurred in 2004.
In the photo above is the massive Iceberg B-15 that blocked access to Weddell seal pupping and penguin colonies during the past
decade. The iceberg led to greatly reduced Weddell pup birth numbers, including the lowest recorded Weddell birth year, 2004, in
the nearly 50 year history of the Weddell seal population study. Photo by Weddell population project PhD recipient Gillian Hadley.
As the giant iceberg began to break up and move out of the area over the next couple of years following the 2004 low, Weddell births skyrocketed to extraordinarily high numbers of new births beginning in 2007, with Weddell pup birth numbers remaining near the 600 level since 2010. Since then, pup birth numbers have hovered near the 600 mark, but have begun to decline ever so slightly since 2010. Last season, 2014, some 603 Weddell pups were born in the study area.
This season, with the sea ice edge so close to the study area so early in the season, it is possible that the number of pups born this year will be off the highs of the past few years. The sea ice may begin to melt more quickly and break up earlier than in the past few years. But project scientists won't know what will actually happen for another two to three weeks or so.
With the number of Weddell births reaching its peak, much of the work of the field team will shift toward completing surveys of the entire Erebus Bay Weddell seal population. There will still be more new pups to tag, and adult seals encountered that have broken or missing tags to replace. The field team will do between 6 to 8 full surveys of the entire study area so that the chances of encountering and recording all of the seals in the study area are extremely high.
The field team is also reweighing pups that have reached the 20 and 35 day marks of their nursing periods. When the 35 day pup weights are taken, those pups that received small temperature/time recording tags will have those tags removed and the data they've recorded retrieved. A few Weddell moms will also be reweighed to continue to assess the accuracy of the new 3D modeling method of weight measurement which is less invasive than coaxing the Weddell moms onto a large livestock scale.
Locating this season's pups for reweighing at the 20 and 35 day points in their nursing periods is often a difficult task for the field team because at this point in the pups' development many pups are swimming much of the time, and often not readily visible to the field team.
Each day the team goes out with an updated list of pups reaching the 20 and 35 day points of their nursing periods, and trys to find those pups until the team has re-weighed every pup on the list.
A Weddell seal mom in the water encourages her young pup to join her in this pair of
photos by field team member and photographer Ross Hinderer.
When the sea ice under the remote camp begins to thin to the point that it is becoming too thin to safely support the weight of the several huts that make up the remote camp, it will be time to pull the camp. The field team can continue to travel to the pupping colonies from McMurdo Station, but the snowmobile drive takes much longer to get to the study area sites, and much of the sea ice in the area becomes melt pools that are more difficult to work around.
Finally, when all of the pups to be weighed at 35 days into their nursing periods have been found and weighed, their temperature tags retrieved, and the final full Weddell seal population survey completed, the field team will begin to carefully pack up all the equipment to be stored at McMurdo Station or shipped back to Montana State University, Bozeman.
Photo from left to right: Weddell seal population project lead scientist Dr. Jay Rotella,
MSU PhD student and field team leader Terrill Paterson, co-principal investigator Dr. Bob Garrott,
and MSU Master's student and field team co-leader Kaitlin Macdonald in the field this season.
Then the population study field season will be over until next year, when the cycle begins anew and the Weddell seals and scientists return to start the pupping season all over again.