Final 2025 Weddell Seal Pupping Season Update By Lead Scientist Prof. Jay Rotella:

The 2025 field season was very productive and scientifically interesting. Sea-ice conditions were unusual in that parts of the study area that are typically ice covered had open water this season. In particular, several locations in the northern portion of the study area that are typically home to Weddell seal pupping colonies did not have sea-ice at all or had only thin layers of newly formed sea ice during the peak of pup births.

The lack of sea ice in those areas in October is something that has only occurred a few times in the past 50 years and allowed the project to learn (a) how seals that normally give birth in those areas responded, (b) how many mothers known to have been born north of the study area chose to give birth in the study area this year, and (c) how seals re-distributed themselves. Although the opportunity to learn from the unusual conditions was welcome, the situation also presented real logistical challenges for getting the field work done.

Notably, open water near the tip of the Erebus Glacier Tongue prevented the team from being able to snowmobile to the northern half of our study area. Fortunately, the team was able to use helicopters to access the northern areas that had ice, which allowed us to keep the long-term database intact and to learn a great deal about the Erebus Bay population.

Preliminary analyses certainly show that the population continues to produce more pups than it did throughout the 1980s and 1990s. The population produced more than 750 pups in 2025, which is something that the project has only recorded happening 2 other times in the past 50 years: all 3 of the highest-production years have been recorded in the last 8 years. Information on total population size, age structure, and survival and breeding rates won’t be revealed until detailed analyses can be done in the months ahead.

In the meantime, we greatly appreciate the additional support that the project received from so many people at McMurdo in helicopter operations, field safety, snowmobile operations and many other support centers. We also appreciate the ongoing support from everyone at McMurdo that helps make our project possible, e.g., cargo, food and housing, science staff, science implementation, science support from the National Science Foundation, military flight crews , flight support staff, travel staff, and so many others. We also really appreciate the daily efforts of everyone on our 2025 field team. It takes so many people to make the project successful. We thank everyone involved and look forward to sharing results as soon as we are able to complete analyses of the long-term database that incorporate information from the fascinating 2025 field season.

– Prof. Jay Rotella, Lead Scientist on the Erebus Bay Weddell Seal Population Study