From Project Lead Scientist Prof. Jay Rotella:

The Erebus Bay population of Weddell seals in Antarctica’s Ross Sea is the most southerly mammal population in the world and the world’s largest population of Weddell seals. The population has been intensively studied annually since the 1960s and provides an excellent opportunity to learn how the population is doing and how the species responds to environmental changes.

Weddell seals are marine predators that rely heavily on fish, so knowing how the population is doing provides valuable information about potential changes in Antarctica’s Ross Sea ecosystem, which is one of the world’s most intact marine ecosystems. Because all pups born in the study area have been tagged each year since the 1970s, the project also provides detailed information about the lives of individuals, including their reproduction, survival, and longevity and how they change across years.

During the 2026 field season, which takes place in October through December during the Antarctic springtime, we will continue the long-term monitoring of the population at Erebus Bay. During the pupping season, the team will uniquely tag each pup born in the study area and associate it with its mother. In recent years, anywhere from ~500 to ~800 pups have been born per year in Erebus Bay, and tagging all of them requires full-time effort from mid-October through mid-November when we repeatedly visit each of the ~10-12 pupping colonies.

We are very interested in learning if pup production this year continues the trend seen in recent decades for the population to produce more pups per year than it did prior to 2000. Starting in early November, we will begin the other major activity of the project’s annual work: population surveys of every individual Weddell seal seen on the ice. We try to conduct 6 surveys of the entire study area during November to mid-December. Surveys are separated by about 5 days, and during each survey we record the identities of all the seals we encounter.

The data from surveys provide valuable information about the population’s size and reveals which animals (both female and male) are still alive and in the study area. Between surveys, we will tag any untagged females and replace any broken or missing tags on seals we encounter.

We are excited to conduct the 2026 field season and to learn how the population is doing, how the many different individuals tagged over the past 5 decades are doing, to see which, if any, records for lifespan and lifetime pup production might be broken, and to train three more early-career ecologists to conduct research on marine mammals in Antarctica. The 2026 field season will be the 25th year in a row that the project has been run out of Montana State University, which is a nice milestone but, of course, just a portion of the longer-term project that has been conducted annually for more than 50 years thanks to the many people that kept the project running and collected the data over so many previous years.

– Prof. Jay Rotella, Principal Investigator, Erebus Bay Weddell Seal Population Study